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PROFESSOR: So last
time, we talked

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about the responses of
auditory nerve fibers

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00:00:32,960 --> 00:00:39,810
and we talked about tonotopic
organization and frequency

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tuning and response areas
of auditory nerve fibers.

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So any questions about that?

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00:00:50,520 --> 00:00:51,780
OK.

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00:00:51,780 --> 00:00:56,270
So this time, today's
lecture was going to go on.

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And the auditory
nerve, of course,

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00:00:57,750 --> 00:00:59,130
leads up into the brain.

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00:01:00,370 --> 00:01:04,280
So we're going to talk
about the auditory central

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nervous system, starting with
the first nucleus in the CNS

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00:01:10,790 --> 00:01:14,526
for the auditory pathway,
which is the cochlear nucleus.

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00:01:15,640 --> 00:01:21,010
And this nucleus gets its name
because the auditory nerve

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is sometimes called
the cochlear nerve.

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Right?

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00:01:23,610 --> 00:01:24,818
It's coming from the cochlea.

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00:01:26,170 --> 00:01:28,430
And so this is the
cochlear nucleus.

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00:01:28,430 --> 00:01:30,560
So can anybody give
me a definition

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00:01:30,560 --> 00:01:35,860
of a nucleus in terms
of a central pathway?

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00:01:35,860 --> 00:01:37,290
Not a cell nucleus.

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00:01:37,290 --> 00:01:38,605
This is a nucleus in the brain.

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00:01:42,130 --> 00:01:43,990
Just a collection of neurons.

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00:01:43,990 --> 00:01:45,000
Right?

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00:01:45,000 --> 00:01:49,975
So a nucleus is a collection of
neurons in the central pathway.

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00:01:49,975 --> 00:01:53,390
A ganglion is a collection of
neurons out in the periphery.

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00:01:53,390 --> 00:01:58,500
So you have the spiral
ganglion in the cochlea,

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00:01:58,500 --> 00:02:01,065
being where the cell bodies
of the auditory nerve fibers--

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00:02:01,065 --> 00:02:03,665
it's called the ganglion there
because it's in the periphery.

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00:02:05,260 --> 00:02:08,570
And that nerve goes into
the central nervous system

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00:02:08,570 --> 00:02:11,570
and it ends on
neurons-- a collection

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00:02:11,570 --> 00:02:14,637
of neurons in the
cochlear nucleus.

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00:02:14,637 --> 00:02:16,845
In the part of the brain
called the cochlear nucleus.

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00:02:18,769 --> 00:02:20,560
We're going to talk in
the cochlear nucleus

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00:02:20,560 --> 00:02:23,810
about the various types
of cells that are there.

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00:02:23,810 --> 00:02:27,690
And instead of just having one
or two types of auditory nerve

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00:02:27,690 --> 00:02:30,640
fibers, as we had
in the periphery,

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00:02:30,640 --> 00:02:34,260
there's going to be a whole
bunch of types of cells.

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00:02:34,260 --> 00:02:36,030
And they have really
fanciful names

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00:02:36,030 --> 00:02:40,450
like octopus cells
and pyramidal cells.

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00:02:40,450 --> 00:02:41,545
So we'll talk about those.

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00:02:42,880 --> 00:02:45,880
When we go into the
cochlear nucleus and record

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00:02:45,880 --> 00:02:48,285
with microelectrodes,
we get single units.

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00:02:49,490 --> 00:02:53,570
And there's a way of classifying
those single units, which

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00:02:53,570 --> 00:02:58,130
was developed here
in the 1960s at MIT,

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00:02:58,130 --> 00:03:01,542
and it was one of the first
applications of computers

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00:03:01,542 --> 00:03:02,750
to the study of neuroscience.

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00:03:04,220 --> 00:03:07,500
Looking at the action potentials
as a function of time,

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00:03:07,500 --> 00:03:10,880
right after you turn
the sound stimulus on.

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00:03:10,880 --> 00:03:12,690
And by looking at
those patterns,

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00:03:12,690 --> 00:03:15,325
you can classify the
units into various types.

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00:03:16,720 --> 00:03:19,710
And now we know a
good correspondence

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00:03:19,710 --> 00:03:22,050
between the physiology
and the anatomy,

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00:03:22,050 --> 00:03:25,363
so we'll go over how we
establish that correspondence.

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00:03:26,730 --> 00:03:29,040
And because these are
these various types,

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00:03:29,040 --> 00:03:31,980
we really have one type of
auditory neurofiber coming in

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00:03:31,980 --> 00:03:35,387
from the periphery, and now
we have a bunch of types.

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00:03:35,387 --> 00:03:36,970
We're now going to
think of the system

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00:03:36,970 --> 00:03:40,770
as having multiple
parallel pathways

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00:03:40,770 --> 00:03:43,420
for the sense of hearing in
the central nervous system.

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00:03:43,420 --> 00:03:48,460
And perhaps one pathway helps
you with one aspect of hearing,

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00:03:48,460 --> 00:03:51,290
and another pathway helps
you with another aspect.

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00:03:53,400 --> 00:03:55,750
And maybe we'll end
up at the end of today

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00:03:55,750 --> 00:03:57,680
with a little bit
of discussion--

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00:03:57,680 --> 00:04:00,380
advanced discussion--
of implants.

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00:04:00,380 --> 00:04:04,580
So we're going to talk about
cochlear implants next week.

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00:04:04,580 --> 00:04:08,760
There is a kind of an implant
called the auditory brainstem

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00:04:08,760 --> 00:04:10,750
implant that's put in
the cochlear nucleus.

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00:04:12,320 --> 00:04:14,820
But here, things
are so complicated.

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00:04:14,820 --> 00:04:18,269
You have a variety of
cell and unit types,

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00:04:18,269 --> 00:04:20,290
each doing a different function.

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00:04:20,290 --> 00:04:21,790
You can imagine
how hard it would

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00:04:21,790 --> 00:04:26,711
be to wire up a prosthesis to
stimulate each one of those

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00:04:26,711 --> 00:04:27,210
correctly.

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00:04:28,560 --> 00:04:31,850
So just let's keep
in mind the challenge

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of putting a prosthesis
into the cochlear nucleus,

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00:04:36,820 --> 00:04:40,130
which is required of people
who lack an auditory nerve.

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00:04:40,130 --> 00:04:42,587
They can't get a
prosthesis in the cochlea

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00:04:42,587 --> 00:04:44,670
because the message wouldn't
be sent to the brain.

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00:04:44,670 --> 00:04:47,140
They need to get a prosthesis
into the cochlear nucleus.

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00:04:47,140 --> 00:04:49,280
But it's very complicated here.

88
00:04:49,280 --> 00:04:52,490
And maybe it's as
complicated processing

89
00:04:52,490 --> 00:04:53,810
as you have in the retina.

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00:04:53,810 --> 00:04:54,310
Right?

91
00:04:54,310 --> 00:04:57,870
In the retina, you have
the retinal ganglion cells

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00:04:57,870 --> 00:04:59,230
being very complicated.

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00:04:59,230 --> 00:05:01,575
Some have center
surround fields.

94
00:05:03,270 --> 00:05:03,850
Right?

95
00:05:03,850 --> 00:05:06,300
There's not just turning
on and turning off.

96
00:05:06,300 --> 00:05:08,050
There's turning on,
there's inhibiting the

97
00:05:08,050 --> 00:05:10,110
on, and so on and so forth.

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00:05:10,110 --> 00:05:12,230
So the cochlear nucleus
I think of a little bit

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00:05:12,230 --> 00:05:16,640
as like the retina equivalent
in the visual system.

100
00:05:19,640 --> 00:05:24,470
OK, so let's look at the
auditory central nervous system

101
00:05:24,470 --> 00:05:27,640
in terms of a block
diagram on the top

102
00:05:27,640 --> 00:05:31,026
and in terms of what it looks
like when you cut sections

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00:05:31,026 --> 00:05:31,775
through the brain.

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00:05:33,210 --> 00:05:35,540
So here's the block diagram.

105
00:05:35,540 --> 00:05:38,590
And we've been talking
about the cochlea here,

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00:05:38,590 --> 00:05:41,980
and the spiral ganglion
is where the cell

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00:05:41,980 --> 00:05:44,540
bodies of the auditory
nerve fibers are.

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00:05:44,540 --> 00:05:47,150
This would be the arrow of
the auditory nerve coming

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00:05:47,150 --> 00:05:50,970
from the spiral ganglion into
the CN, the cochlear nucleus.

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00:05:52,230 --> 00:05:55,110
And of course you have one
of those on the left side,

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00:05:55,110 --> 00:05:56,960
and another on the right side.

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00:05:56,960 --> 00:06:00,750
So this diagram is showing both
sides of the central pathway.

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00:06:02,370 --> 00:06:07,600
From the cochlear nucleus, the
neurons of the cochlear nucleus

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00:06:07,600 --> 00:06:09,845
send axons to a
variety of places.

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00:06:11,940 --> 00:06:15,590
One of them is in the region
of the brain called the pons.

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00:06:15,590 --> 00:06:18,780
And in the pons
there is a complex

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00:06:18,780 --> 00:06:21,460
called the superior
olivary complex.

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00:06:22,570 --> 00:06:25,140
And it's abbreviated SOC here.

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00:06:25,140 --> 00:06:26,660
So what's a complex?

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00:06:26,660 --> 00:06:31,460
Now, we've had a ganglion,
a nucleus, and a complex.

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00:06:31,460 --> 00:06:34,140
Well, as we'll see
in a couple of weeks

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00:06:34,140 --> 00:06:36,710
in the course, when
we talk about the SOC,

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00:06:36,710 --> 00:06:42,820
it has a whole bunch of nuclei
very closely spaced within it.

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00:06:42,820 --> 00:06:44,955
Maybe a dozen or so
different nuclei.

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00:06:45,960 --> 00:06:48,400
Each of which is a different
collection of cells.

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00:06:48,400 --> 00:06:51,846
So the whole thing is called
a superior olivary complex.

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00:06:54,520 --> 00:06:56,500
And superior olive?

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00:06:56,500 --> 00:06:58,080
What's that part of the name?

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00:06:58,080 --> 00:07:00,610
So has anybody heard
about the olive?

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00:07:00,610 --> 00:07:02,090
Or the inferior olive?

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00:07:03,400 --> 00:07:04,935
What's the olive?

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00:07:04,935 --> 00:07:06,350
We should talk about it.

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00:07:09,272 --> 00:07:10,250
Nothing?

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00:07:10,250 --> 00:07:10,760
Anybody?

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00:07:10,760 --> 00:07:12,460
Any ideas?

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00:07:12,460 --> 00:07:14,030
So it's involved in
the motor system.

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00:07:15,290 --> 00:07:17,000
And if you cut a
section of the brain--

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00:07:17,000 --> 00:07:19,510
it's not illustrated
here, but if you

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00:07:19,510 --> 00:07:24,570
look at a section of the brain
in transverse sections, which

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00:07:24,570 --> 00:07:31,300
are the kind of sections
that we have here--

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00:07:31,300 --> 00:07:36,490
you find a structure that's
kind of gotten wrinkled edges

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00:07:36,490 --> 00:07:39,405
and sort of has a central pit,
and it looks like an olive.

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00:07:41,860 --> 00:07:45,420
At least it did to the first
neuro-anatomists, maybe

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00:07:45,420 --> 00:07:47,560
who had their eye on the
clock, and were waiting

145
00:07:47,560 --> 00:07:48,902
for the 5 o'clock dinner call.

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00:07:48,902 --> 00:07:50,610
They said, hey, that
looks like an olive.

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00:07:52,510 --> 00:07:56,029
And they probably didn't
have very good microscopes,

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00:07:56,029 --> 00:07:58,070
so they were looking at
things at very low power.

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00:07:59,720 --> 00:08:02,290
And what happened later
is somebody discovered

150
00:08:02,290 --> 00:08:07,930
another complex over here that
was nearby but didn't look

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00:08:07,930 --> 00:08:10,550
anything like an olive,
but it was near the olive.

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00:08:11,820 --> 00:08:14,700
And it was a little bit
rostral in the brain,

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00:08:14,700 --> 00:08:17,616
and things that are rostral
are called superior.

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00:08:21,050 --> 00:08:24,340
So they called this
the superior olive,

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00:08:24,340 --> 00:08:28,210
and this has become known
as the inferior olive.

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00:08:30,030 --> 00:08:33,690
And after they got even
higher power magnification,

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00:08:33,690 --> 00:08:37,590
they could see this was
really a complex of nuclei,

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00:08:37,590 --> 00:08:40,213
so they called it the
superior olivary complex.

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00:08:42,750 --> 00:08:43,935
OK, so this is motor.

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00:08:46,320 --> 00:08:47,495
And this is auditory.

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00:08:50,200 --> 00:08:53,030
And they just happen to be
located near one another

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00:08:53,030 --> 00:08:57,900
in the brainstem, in the area of
the brainstem called the pons,

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00:08:57,900 --> 00:08:58,460
down here.

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00:08:58,460 --> 00:09:03,550
So these are sections
of the human brain.

165
00:09:03,550 --> 00:09:04,676
So why do we cut sections?

166
00:09:06,080 --> 00:09:06,580
Anybody?

167
00:09:10,963 --> 00:09:12,430
AUDIENCE: To look
at the anatomy?

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00:09:12,430 --> 00:09:13,500
PROFESSOR: To look
at the anatomy.

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00:09:13,500 --> 00:09:14,000
Right.

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00:09:14,000 --> 00:09:16,710
So a compound microscope
that we usually

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00:09:16,710 --> 00:09:21,020
use to look at the anatomy can't
look at a big hunk of tissue.

172
00:09:21,020 --> 00:09:22,150
You have to cut sections.

173
00:09:22,150 --> 00:09:26,240
And the thinner section you cut,
the better resolution you get.

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00:09:26,240 --> 00:09:29,950
Because you can bring a
very high-powered objective

175
00:09:29,950 --> 00:09:32,740
and look at very
fine cellular detail.

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00:09:32,740 --> 00:09:36,830
So cutting sections is what
neuro-anatomists love to do.

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00:09:36,830 --> 00:09:39,770
An example thickness
of a section

178
00:09:39,770 --> 00:09:40,913
might be 10 micrometers.

179
00:09:42,640 --> 00:09:45,370
100 micrometers is a
very thick section.

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00:09:46,570 --> 00:09:48,770
So you can imagine
how many sections

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00:09:48,770 --> 00:09:51,104
you'd have to
chunk through to go

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00:09:51,104 --> 00:09:52,520
through the whole
human brainstem.

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00:09:52,520 --> 00:09:55,830
That's why it's nice to work
with small animals like mice.

184
00:09:55,830 --> 00:09:57,390
They don't have
as many sections.

185
00:09:57,390 --> 00:09:57,890
Right?

186
00:09:59,080 --> 00:10:02,770
So, but these are sections
of the human brainstem.

187
00:10:02,770 --> 00:10:05,220
And here, this word
says spiral ganglion,

188
00:10:05,220 --> 00:10:07,340
so this is the auditory
nerve coming in.

189
00:10:08,950 --> 00:10:10,460
And this is the
cochlear nucleus.

190
00:10:12,610 --> 00:10:15,870
And I've heard it
described that by the time

191
00:10:15,870 --> 00:10:19,195
the sense of hearing came
along, the brain was formed.

192
00:10:20,280 --> 00:10:22,840
Primitive animals had the brain,
and all the other functions

193
00:10:22,840 --> 00:10:24,270
like motor.

194
00:10:24,270 --> 00:10:26,720
So there wasn't any
room in the middle.

195
00:10:26,720 --> 00:10:29,780
So it was stuck on the outside.

196
00:10:29,780 --> 00:10:32,070
The sense of hearing--
the cochlear nucleus,

197
00:10:32,070 --> 00:10:33,950
at least, was put on
the outside of the brain

198
00:10:33,950 --> 00:10:36,074
because there wasn't any
room for it in the inside.

199
00:10:37,230 --> 00:10:39,150
Cochlear nucleus
structures tend to be

200
00:10:39,150 --> 00:10:40,982
superficial in the brainstem.

201
00:10:40,982 --> 00:10:42,190
This is the cochlear nucleus.

202
00:10:44,150 --> 00:10:47,460
And these are the
axons crossing.

203
00:10:47,460 --> 00:10:49,770
Because some of the
cochlear nucleus axons

204
00:10:49,770 --> 00:10:52,520
cross from the left
side to the right side.

205
00:10:55,050 --> 00:11:01,960
And the superior olivary complex
is deep within the brainstem.

206
00:11:03,880 --> 00:11:06,800
But some of the
cochlear nucleus axons

207
00:11:06,800 --> 00:11:08,190
don't go to the superior olive.

208
00:11:08,190 --> 00:11:10,070
They bypass it
and go all the way

209
00:11:10,070 --> 00:11:12,735
to the IC, the
inferior colliculus.

210
00:11:16,490 --> 00:11:18,220
That's at the level
of the mid-brain.

211
00:11:18,220 --> 00:11:20,070
So this is the
inferior colliculus.

212
00:11:20,070 --> 00:11:22,770
So you've studied a
collicular structure before.

213
00:11:22,770 --> 00:11:23,291
What was it?

214
00:11:23,291 --> 00:11:23,790
Right?

215
00:11:27,100 --> 00:11:29,280
In the first half
of this course.

216
00:11:29,280 --> 00:11:31,860
The superior colliculus, right?

217
00:11:31,860 --> 00:11:33,470
So why is it superior?

218
00:11:33,470 --> 00:11:34,370
Is it better?

219
00:11:35,230 --> 00:11:35,730
No.

220
00:11:35,730 --> 00:11:39,460
It's just a little
rostral in the brain.

221
00:11:39,460 --> 00:11:42,290
So if you cut
sections from caudal--

222
00:11:42,290 --> 00:11:45,330
so this is the spinal cord
down, and your microtome's

223
00:11:45,330 --> 00:11:48,070
chunking through the
medulla, and the pons,

224
00:11:48,070 --> 00:11:49,699
and you get to the midbrain.

225
00:11:49,699 --> 00:11:51,990
And then you cut through the
inferior colliculus, which

226
00:11:51,990 --> 00:11:54,810
is right here, and then a
little bit more rostral,

227
00:11:54,810 --> 00:11:57,510
you cut through the
superior colliculi,

228
00:11:57,510 --> 00:11:58,440
which are right here.

229
00:11:59,299 --> 00:12:00,840
And they tend to be
a little flatter.

230
00:12:02,050 --> 00:12:06,970
These inferior colliculi
are more dome-like shaped.

231
00:12:06,970 --> 00:12:08,920
So what does colliculus mean?

232
00:12:10,507 --> 00:12:11,340
Anybody know French?

233
00:12:13,340 --> 00:12:14,070
Who knows French?

234
00:12:14,070 --> 00:12:16,122
Come on, somebody knows.

235
00:12:16,122 --> 00:12:16,955
OK, who knows Latin?

236
00:12:18,490 --> 00:12:20,210
OK, well, that's
the expected result.

237
00:12:21,440 --> 00:12:23,190
Colliculus means a little hill.

238
00:12:24,660 --> 00:12:26,980
And this lives up to its name.

239
00:12:26,980 --> 00:12:30,660
These are little hills right
on the top of the brainstem.

240
00:12:33,430 --> 00:12:36,610
The Inferior colliculi
are here, left and right,

241
00:12:36,610 --> 00:12:38,200
and the superior
colliculi are here.

242
00:12:38,200 --> 00:12:41,100
So what is the
superior colliculus--

243
00:12:41,100 --> 00:12:43,005
what does the
superior colliculi do?

244
00:12:46,330 --> 00:12:48,795
What happens when you stimulate
in the superior colliculus?

245
00:12:50,150 --> 00:12:51,670
Your eyeballs move, right?

246
00:12:53,460 --> 00:12:56,050
So the superior
colliculus is intimately

247
00:12:56,050 --> 00:13:00,011
involved in saccadic
eye movements.

248
00:13:00,011 --> 00:13:00,510
Right?

249
00:13:00,510 --> 00:13:03,052
You guys must have
talked a lot about that

250
00:13:03,052 --> 00:13:04,385
in the first part of the course.

251
00:13:05,830 --> 00:13:08,580
And the inferior
colliculus, what does it do?

252
00:13:08,580 --> 00:13:11,660
Well, I've heard people who
have spent their whole research

253
00:13:11,660 --> 00:13:14,600
career studying the
inferior colliculus,

254
00:13:14,600 --> 00:13:16,940
and they say, well, I
don't know what it does!

255
00:13:18,890 --> 00:13:22,330
That's not an uncommon statement
in the sense of hearing.

256
00:13:22,330 --> 00:13:25,280
So the inferior
colliculus certainly

257
00:13:25,280 --> 00:13:28,870
is a meeting place for
lots of axons coming up

258
00:13:28,870 --> 00:13:33,770
from the cochlear nuclei, from
the superior olivary complex.

259
00:13:33,770 --> 00:13:35,785
It's a midbrain meeting center.

260
00:13:37,640 --> 00:13:40,360
It's certainly involved
with many parts

261
00:13:40,360 --> 00:13:41,910
of the sense of
hearing, but we don't

262
00:13:41,910 --> 00:13:45,800
know exactly what role it plays.

263
00:13:45,800 --> 00:13:49,000
Certainly not as simple
as it moves ears, OK?

264
00:13:50,180 --> 00:13:52,570
Whereas the superior
colliculus moves eyes.

265
00:13:55,150 --> 00:13:58,780
All right, coming up the
pathway even further,

266
00:13:58,780 --> 00:14:02,890
the next level is the
thalamus, where you have,

267
00:14:02,890 --> 00:14:05,205
for the auditory system,
the medial geniculate.

268
00:14:07,290 --> 00:14:10,005
And what was the analog
in the visual pathway?

269
00:14:11,070 --> 00:14:12,640
A lateral geniculate, right?

270
00:14:12,640 --> 00:14:18,050
OK, so in the brain, medial is
toward the middle and lateral

271
00:14:18,050 --> 00:14:20,500
is a little bit toward
the lateral part.

272
00:14:20,500 --> 00:14:23,320
You don't have the lateral
geniculate in this section,

273
00:14:23,320 --> 00:14:25,860
but it would be a
little bit lateral

274
00:14:25,860 --> 00:14:27,100
to the medial geniculate.

275
00:14:27,100 --> 00:14:29,075
And what does geniculate mean?

276
00:14:30,858 --> 00:14:32,230
AUDIENCE: Knee.

277
00:14:32,230 --> 00:14:32,950
PROFESSOR: Knee.

278
00:14:32,950 --> 00:14:33,710
Right.

279
00:14:33,710 --> 00:14:35,390
A genu is a knee.

280
00:14:35,390 --> 00:14:38,690
And the lateral geniculate--
if you use your imagination

281
00:14:38,690 --> 00:14:41,300
and if you were an
early neuro-anatomists

282
00:14:41,300 --> 00:14:43,810
with a low-power lens
on your microscope,

283
00:14:43,810 --> 00:14:45,400
it looked like a bent knee.

284
00:14:45,400 --> 00:14:47,080
It's sort of bent.

285
00:14:47,080 --> 00:14:49,320
The medial geniculate
is not that at all.

286
00:14:49,320 --> 00:14:51,510
It doesn't look at
all like a knee.

287
00:14:51,510 --> 00:14:55,000
But it's just medial to
the lateral geniculate,

288
00:14:55,000 --> 00:14:57,620
so that's how it got its name.

289
00:14:57,620 --> 00:14:58,800
OK, very good answer.

290
00:15:00,475 --> 00:15:01,350
What is to genuflect?

291
00:15:02,770 --> 00:15:03,520
AUDIENCE: To bend.

292
00:15:03,520 --> 00:15:04,000
AUDIENCE: Kneel.

293
00:15:04,000 --> 00:15:05,000
PROFESSOR: That's right.

294
00:15:05,000 --> 00:15:06,795
To kneel down, bend your knees.

295
00:15:06,795 --> 00:15:07,415
Ah, king!

296
00:15:07,415 --> 00:15:07,915
Ruler!

297
00:15:11,300 --> 00:15:12,450
All right.

298
00:15:12,450 --> 00:15:16,975
And then finally we have
the auditory cortex, the AC,

299
00:15:16,975 --> 00:15:18,880
in those boxes at the top.

300
00:15:18,880 --> 00:15:21,290
And the auditory
cortical fields are

301
00:15:21,290 --> 00:15:25,370
in the temporal cortex
on the sides of the head.

302
00:15:25,370 --> 00:15:29,310
So I'm pointing to my
left temporal cortex

303
00:15:29,310 --> 00:15:31,582
if I could go through my skull.

304
00:15:31,582 --> 00:15:33,265
It's behind the temporal bone.

305
00:15:34,890 --> 00:15:36,510
OK, where were the visual areas?

306
00:15:37,890 --> 00:15:38,770
Back here.

307
00:15:38,770 --> 00:15:43,120
This is called the
occipital cortex, right?

308
00:15:43,120 --> 00:15:45,690
In a completely different
part of the cortex.

309
00:15:47,340 --> 00:15:50,150
And in the primate--
of course, humans

310
00:15:50,150 --> 00:15:54,055
are primates-- you have a big
temporal lobe of the brain.

311
00:15:55,380 --> 00:15:57,820
And that's this lobe here.

312
00:15:57,820 --> 00:16:01,310
And the auditory cortical
fields, for the most part,

313
00:16:01,310 --> 00:16:04,860
are on the dorsal
surface of that.

314
00:16:06,210 --> 00:16:10,490
And you have to go down
inside the temporal gyrus--

315
00:16:10,490 --> 00:16:13,160
this big gyrus-- to
look and see them,

316
00:16:13,160 --> 00:16:14,900
because they're
not on the surface

317
00:16:14,900 --> 00:16:16,620
of the brain in the primate.

318
00:16:16,620 --> 00:16:19,640
They're down inside
the temporal gyrus.

319
00:16:23,760 --> 00:16:26,610
Well, how does this look
compared to the visual pathway?

320
00:16:29,900 --> 00:16:32,170
Let's say this is
the retina here.

321
00:16:33,740 --> 00:16:34,460
OK?

322
00:16:34,460 --> 00:16:36,005
Where does the retina project?

323
00:16:38,150 --> 00:16:39,525
That's a great exam question!

324
00:16:41,475 --> 00:16:42,725
Where does the retina project?

325
00:16:49,850 --> 00:16:52,320
That's not a one
answer question, right?

326
00:16:54,150 --> 00:16:56,360
In large parts of the LGM.

327
00:16:56,360 --> 00:16:57,092
That's right.

328
00:16:57,092 --> 00:16:58,216
Where else does it project?

329
00:16:59,289 --> 00:17:00,164
AUDIENCE: [INAUDIBLE]

330
00:17:01,332 --> 00:17:02,790
PROFESSOR: I don't
know about that.

331
00:17:02,790 --> 00:17:05,980
Certainly projects to the
superior colliculus, right?

332
00:17:07,132 --> 00:17:10,880
Aren't the x and
y cells projecting

333
00:17:10,880 --> 00:17:12,004
to the superior colliculus?

334
00:17:13,450 --> 00:17:17,690
A few of the retinal
ganglion cells

335
00:17:17,690 --> 00:17:19,300
project to the
superior colliculus.

336
00:17:19,300 --> 00:17:20,819
You better ask Peter for sure.

337
00:17:20,819 --> 00:17:23,119
Obviously, I don't know much
about the visual pathway.

338
00:17:23,119 --> 00:17:25,680
But so how does that look here?

339
00:17:25,680 --> 00:17:28,710
We have the cochlea, and
even the cochlear nucleus.

340
00:17:28,710 --> 00:17:31,710
Does it project
to the geniculate?

341
00:17:31,710 --> 00:17:33,360
No, not at all.

342
00:17:33,360 --> 00:17:38,840
Between the periphery
and the thalamic level

343
00:17:38,840 --> 00:17:42,330
for the auditory pathway, you
have the cochlear nucleus.

344
00:17:42,330 --> 00:17:44,890
You have the superior
olivary complex.

345
00:17:44,890 --> 00:17:47,390
And you have the
inferior colliculus.

346
00:17:47,390 --> 00:17:54,560
And these structures are on the
main highway up to the cortex.

347
00:17:54,560 --> 00:17:57,830
It's not as if the
main pathway bypasses

348
00:17:57,830 --> 00:17:58,830
the inferior colliculus.

349
00:17:58,830 --> 00:18:03,010
This little side arrow
is just a few axons.

350
00:18:03,010 --> 00:18:06,750
The main pathway
is cochlear nucleus

351
00:18:06,750 --> 00:18:08,930
to superior olivary complex.

352
00:18:08,930 --> 00:18:12,510
And, to a certain extent,
cochlear nucleus to IC.

353
00:18:12,510 --> 00:18:14,590
Superior olivary complex to IC.

354
00:18:14,590 --> 00:18:17,190
And then to medial geniculate.

355
00:18:17,190 --> 00:18:19,240
So it's a big difference

356
00:18:19,240 --> 00:18:22,610
What about the
somatosensory system?

357
00:18:22,610 --> 00:18:29,260
You have a dorsal root ganglia
in the somatosensory system,

358
00:18:29,260 --> 00:18:31,350
and they project
actually all the way

359
00:18:31,350 --> 00:18:34,900
to the somatosensory
regions of the thalamus.

360
00:18:34,900 --> 00:18:36,590
So that's more like
the visual system.

361
00:18:36,590 --> 00:18:39,730
There's something
different going on here

362
00:18:39,730 --> 00:18:41,150
in the auditory system.

363
00:18:41,150 --> 00:18:46,590
There's a whole bunch of
brainstem and midbrain nuclei

364
00:18:46,590 --> 00:18:48,440
in the auditory
pathway that you don't

365
00:18:48,440 --> 00:18:50,195
have represented in
these other systems.

366
00:18:51,650 --> 00:18:57,640
So we're going to learn,
in about two weeks,

367
00:18:57,640 --> 00:19:00,290
about the superior
olivary complex

368
00:19:00,290 --> 00:19:01,600
and the inferior colliculus.

369
00:19:01,600 --> 00:19:04,730
These extra brainstem
nuclei are very involved

370
00:19:04,730 --> 00:19:07,066
in the process of
sound localization.

371
00:19:09,940 --> 00:19:12,490
And that's because for
the auditory system

372
00:19:12,490 --> 00:19:17,650
to figure out where a sound
is coming from, in best case

373
00:19:17,650 --> 00:19:19,070
we use the two ears.

374
00:19:20,240 --> 00:19:24,450
And we use cues like the
difference in time of arrival

375
00:19:24,450 --> 00:19:29,150
of a sound at the two ears, and
the difference in sound level

376
00:19:29,150 --> 00:19:32,460
at the two ears, to figure out
where a sound is coming from.

377
00:19:32,460 --> 00:19:34,420
Certainly in the
azimuthal plane.

378
00:19:35,810 --> 00:19:40,230
And in the visual system, and
in the somatosensory system,

379
00:19:40,230 --> 00:19:43,130
the localization of where
the stimulus is coming from

380
00:19:43,130 --> 00:19:45,860
is mapped right
at the periphery.

381
00:19:45,860 --> 00:19:49,580
So you know that
a spot of light is

382
00:19:49,580 --> 00:19:52,360
coming from over to
your right because it

383
00:19:52,360 --> 00:19:55,850
hits your nasal retina
in your right eye,

384
00:19:55,850 --> 00:19:58,510
and your temporal
retina in your left eye.

385
00:19:58,510 --> 00:20:02,200
So that position
information is already

386
00:20:02,200 --> 00:20:04,300
available in the periphery.

387
00:20:04,300 --> 00:20:07,060
In the sense of hearing,
what does the periphery map?

388
00:20:08,800 --> 00:20:11,150
It maps sound frequency, right?

389
00:20:11,150 --> 00:20:14,880
So obviously, sound
frequency is a very important

390
00:20:14,880 --> 00:20:16,260
characteristic.

391
00:20:16,260 --> 00:20:18,410
It allows you to
identify the sound.

392
00:20:18,410 --> 00:20:21,560
But it doesn't help you to tell
where the sound is coming from.

393
00:20:21,560 --> 00:20:24,660
And if you're a mouse
running away from a cat,

394
00:20:24,660 --> 00:20:28,140
and it's night time, and
you can't see the cat,

395
00:20:28,140 --> 00:20:31,270
you need to know where the
cat sound is coming from.

396
00:20:31,270 --> 00:20:34,520
Is it coming from your right,
or is it coming from your left?

397
00:20:34,520 --> 00:20:38,430
And it takes a lot of
brainstem processing,

398
00:20:38,430 --> 00:20:42,040
comparing the inputs
from the two sides,

399
00:20:42,040 --> 00:20:45,410
to reconstruct where the
sound was coming from.

400
00:20:45,410 --> 00:20:49,310
Especially if you're doing
it by intra-aural time

401
00:20:49,310 --> 00:20:51,000
and intra-aural
level differences.

402
00:20:51,000 --> 00:20:54,760
So all of this brain stem
processing-- or much of it--

403
00:20:54,760 --> 00:20:59,820
is devoted to figuring out
where the sound is coming from.

404
00:20:59,820 --> 00:21:02,500
It's figuring out the
location of the sound.

405
00:21:02,500 --> 00:21:06,200
So we'll spend a good
week or more on that,

406
00:21:06,200 --> 00:21:07,850
in a couple weeks in our course.

407
00:21:07,850 --> 00:21:10,210
Because that's one
of the things you

408
00:21:10,210 --> 00:21:12,750
can really sink your teeth
in, in the auditory system.

409
00:21:12,750 --> 00:21:15,810
The thing it does
is to figure out

410
00:21:15,810 --> 00:21:18,190
where the location of
the sound source is.

411
00:21:25,900 --> 00:21:29,400
OK, now we're going to spend
the rest of the lecture

412
00:21:29,400 --> 00:21:31,000
today on the cochlear nucleus.

413
00:21:31,000 --> 00:21:34,040
The very first nucleus
in the auditory pathway.

414
00:21:35,690 --> 00:21:40,010
And we're first going to
talk about basic things

415
00:21:40,010 --> 00:21:44,610
like the anatomy of the cochlear
nucleus and its tonotopy.

416
00:21:46,730 --> 00:21:51,610
So this is a drawing
of the cochlear nucleus

417
00:21:51,610 --> 00:21:53,470
in the so-called sagittal plane.

418
00:21:58,620 --> 00:22:01,270
We should all know what
the sagittal plane is.

419
00:22:06,800 --> 00:22:09,240
Can anybody explain it to me?

420
00:22:09,240 --> 00:22:10,880
Or can anybody explain?

421
00:22:10,880 --> 00:22:11,380
Yeah?

422
00:22:13,000 --> 00:22:14,530
Right like this.

423
00:22:14,530 --> 00:22:19,210
So I like to think of it as the
zodiac character Sagittarius.

424
00:22:19,210 --> 00:22:19,710
Right?

425
00:22:19,710 --> 00:22:20,543
Who was Sagittarius?

426
00:22:21,210 --> 00:22:22,240
AUDIENCE: [INAUDIBLE].

427
00:22:22,240 --> 00:22:23,365
PROFESSOR: He was the what?

428
00:22:23,365 --> 00:22:24,520
AUDIENCE: He was an archer.

429
00:22:24,520 --> 00:22:26,470
PROFESSOR: Yes,
he was an archer.

430
00:22:26,470 --> 00:22:29,055
Happened to have a
horse behind him.

431
00:22:29,055 --> 00:22:30,290
Or for his behind.

432
00:22:32,940 --> 00:22:36,060
So he shot the arrow, and
if he shot it effectively,

433
00:22:36,060 --> 00:22:37,853
he'd hit me right in
the center of my head,

434
00:22:37,853 --> 00:22:41,240
and my two halves of my
brain would fall apart.

435
00:22:41,240 --> 00:22:44,080
And if you picked one
half up and looked at it,

436
00:22:44,080 --> 00:22:45,990
you would a sagittal section.

437
00:22:45,990 --> 00:22:47,331
OK?

438
00:22:47,331 --> 00:22:48,950
Of my brain.

439
00:22:48,950 --> 00:22:51,600
And the cochlear nucleus,
as we saw before,

440
00:22:51,600 --> 00:22:53,255
is hanging off the
side of the brain.

441
00:22:55,990 --> 00:22:58,165
But if that archer
shot-- instead of right

442
00:22:58,165 --> 00:23:01,800
at the midline, shot
a little off-center,

443
00:23:01,800 --> 00:23:05,470
and the cochlear
nucleus half fell away,

444
00:23:05,470 --> 00:23:11,730
you'd get this sagittal section
of the cochlear nucleus.

445
00:23:11,730 --> 00:23:16,220
And so the cochlea is down
here and the auditory nerve

446
00:23:16,220 --> 00:23:19,770
is coming up into
the cochlear nucleus.

447
00:23:19,770 --> 00:23:21,055
So what is up on this section?

448
00:23:21,055 --> 00:23:25,000
Well, it's going
dorsal, going higher.

449
00:23:25,000 --> 00:23:26,055
So here's your compass.

450
00:23:27,056 --> 00:23:29,420
The cochlear nucleus is ventral.

451
00:23:29,420 --> 00:23:31,320
The auditory nerve
climbs up dorsally

452
00:23:31,320 --> 00:23:32,680
into the cochlear nucleus.

453
00:23:34,680 --> 00:23:41,370
And that compass
gives you two clues

454
00:23:41,370 --> 00:23:45,070
about the two big divisions
of the cochlear nucleus.

455
00:23:45,070 --> 00:23:47,320
This biggest part of
the cochlear nucleus

456
00:23:47,320 --> 00:23:49,272
is called the ventral
cochlear nucleus,

457
00:23:49,272 --> 00:23:50,355
because it's down ventral.

458
00:23:51,950 --> 00:23:55,080
The VCN is the ventral
cochlear nucleus.

459
00:23:56,770 --> 00:23:59,410
And the other part is the DCN.

460
00:23:59,410 --> 00:24:00,964
That's the dorsal
cochlear nucleus.

461
00:24:00,964 --> 00:24:02,630
This is the part that
comes up dorsally.

462
00:24:07,960 --> 00:24:09,330
And they look different.

463
00:24:09,330 --> 00:24:13,020
If you look at the VCN, it looks
like sort of a homogeneous mass

464
00:24:13,020 --> 00:24:15,115
of cells without a huge
amount of organization.

465
00:24:16,210 --> 00:24:18,930
But as you can see by
these dash lines here,

466
00:24:18,930 --> 00:24:21,555
the DCN has layers in it.

467
00:24:24,910 --> 00:24:29,237
And people have pushed
the idea that the DCN

468
00:24:29,237 --> 00:24:30,320
is like a mini-cerebellum.

469
00:24:31,700 --> 00:24:34,300
| know, the cerebellum is
at the back of your brain.

470
00:24:34,300 --> 00:24:37,700
Cerebellum means it's
a part of your brain

471
00:24:37,700 --> 00:24:39,340
that deals with motor functions.

472
00:24:39,340 --> 00:24:41,750
And has these beautiful layers.

473
00:24:41,750 --> 00:24:44,690
Certain kinds of cells
are in each layer.

474
00:24:44,690 --> 00:24:48,650
And there is an analogy between
the DCN and the cerebellum.

475
00:24:48,650 --> 00:24:52,420
It certainly works as
far as the layers goes.

476
00:24:52,420 --> 00:24:54,130
Some of the cell
types are the same.

477
00:24:54,130 --> 00:24:57,320
You have lots of
little granule cells

478
00:24:57,320 --> 00:25:00,396
in the cerebellum and the
dorsal cochlear nucleus.

479
00:25:00,396 --> 00:25:03,155
You have pyramidal
cells in layer two.

480
00:25:05,010 --> 00:25:08,475
The ventral cochlear nucleus, by
contrast, is very homogeneous.

481
00:25:10,290 --> 00:25:14,660
Now this slide shows you,
in sagittal view, not only

482
00:25:14,660 --> 00:25:17,170
the cochlear nucleus
and the subdivisions,

483
00:25:17,170 --> 00:25:20,820
but it shows you some labeled
auditory nerve fibers coming

484
00:25:20,820 --> 00:25:22,400
in, in the auditory nerve.

485
00:25:22,400 --> 00:25:24,215
So we talked about
labeling before.

486
00:25:25,990 --> 00:25:28,520
We talked about how you can
put a microelectrode filled

487
00:25:28,520 --> 00:25:31,360
with neural tracer
in the auditory nerve

488
00:25:31,360 --> 00:25:35,410
and get the tuning curve and
the characteristic frequency,

489
00:25:35,410 --> 00:25:39,390
or CF, way down at the
tip of the tuning cure.

490
00:25:39,390 --> 00:25:41,210
And then you can
inject a neural tracer.

491
00:25:42,860 --> 00:25:46,430
And the last time, we talked
about labeling and tracing

492
00:25:46,430 --> 00:25:49,780
the auditory nerve fibers in the
cochlea to the inner hair cell

493
00:25:49,780 --> 00:25:51,180
that it contacted.

494
00:25:51,180 --> 00:25:54,050
But you can just as easily
go the other direction.

495
00:25:54,050 --> 00:25:57,710
Neural tracers fill
the entire neuron.

496
00:25:57,710 --> 00:25:59,840
So these fibers were
labeled, and now we're

497
00:25:59,840 --> 00:26:02,130
looking at their
central trajectory

498
00:26:02,130 --> 00:26:04,590
into the central part
of the auditory nerve

499
00:26:04,590 --> 00:26:05,840
and into the cochlear nucleus.

500
00:26:08,230 --> 00:26:11,680
And it's pretty hard to read,
but if you could read them,

501
00:26:11,680 --> 00:26:14,910
these arrows and the
numbers following them

502
00:26:14,910 --> 00:26:18,190
indicate the
characteristic frequency

503
00:26:18,190 --> 00:26:22,235
of each of four different
labeled auditory nerve fibers.

504
00:26:23,420 --> 00:26:30,270
This one way down here has
a CF of 0.17 kilohertz.

505
00:26:30,270 --> 00:26:35,110
This one is a CF of 2.7.

506
00:26:35,110 --> 00:26:39,380
This is a CF of 10.3.

507
00:26:39,380 --> 00:26:45,650
And the top one, I think,
is a CF of 36 kilohertz.

508
00:26:45,650 --> 00:26:50,000
And you can easily see
a progression from low

509
00:26:50,000 --> 00:26:54,910
CF's to mid CF's to high CF's.

510
00:26:54,910 --> 00:26:57,940
So 36 kilohertz is way
beyond the upper limit

511
00:26:57,940 --> 00:27:01,670
of human hearing, but in this
experimental animal, which

512
00:27:01,670 --> 00:27:05,750
was a cat-- cats hear up to 50
kilohertz, at least an octave

513
00:27:05,750 --> 00:27:09,170
above the upper
limit of our hearing.

514
00:27:09,170 --> 00:27:11,150
And they have auditory
trainer fibers

515
00:27:11,150 --> 00:27:13,280
that respond quite
well at 36 kilohertz.

516
00:27:14,930 --> 00:27:19,720
So you can see that
there is a organization,

517
00:27:19,720 --> 00:27:21,760
and this organization
could be called

518
00:27:21,760 --> 00:27:35,510
a tonotopic organization--
for the projection

519
00:27:35,510 --> 00:27:39,940
of the auditory nerve
onto the cochlear nucleus

520
00:27:39,940 --> 00:27:44,800
and you can bet, than, that
if you were to explore around

521
00:27:44,800 --> 00:27:47,735
here-- in the DCN that
we've been talking about--

522
00:27:47,735 --> 00:27:52,840
if you were to record here with
an electrode that's sampled not

523
00:27:52,840 --> 00:27:55,900
from the auditory nerve
fibers but from the cell

524
00:27:55,900 --> 00:27:57,680
bodies of the cochlear nucleus.

525
00:27:57,680 --> 00:28:00,540
And you can design
electrodes to record

526
00:28:00,540 --> 00:28:03,940
from either fibers
and no neurons,

527
00:28:03,940 --> 00:28:06,170
or neurons and no fibers.

528
00:28:06,170 --> 00:28:09,950
If you were to use the latter,
and sample from the neurons

529
00:28:09,950 --> 00:28:14,176
here, you would expect them
to respond to low frequencies.

530
00:28:16,890 --> 00:28:19,660
Whereas if you were to
record from way up there,

531
00:28:19,660 --> 00:28:22,600
you'd expect the neurons
to record and respond

532
00:28:22,600 --> 00:28:23,910
to high frequencies.

533
00:28:23,910 --> 00:28:25,285
And in fact, that's
what happens.

534
00:28:26,470 --> 00:28:30,420
And these kinds of electrode
mappings of the cochlear

535
00:28:30,420 --> 00:28:32,735
nucleus have been
done for many years.

536
00:28:34,050 --> 00:28:38,230
These are data from the
'50s from the University

537
00:28:38,230 --> 00:28:39,690
of Wisconsin.

538
00:28:39,690 --> 00:28:44,790
So what's done here
is an electrode is

539
00:28:44,790 --> 00:28:50,300
put through the cochlear nucleus
and each 100 micrometers or so,

540
00:28:50,300 --> 00:28:55,040
it's stopped to record from,
in this case, cochlear nucleus

541
00:28:55,040 --> 00:28:55,670
cells.

542
00:28:55,670 --> 00:28:59,430
And their CF's are indicated
by the many numbers

543
00:28:59,430 --> 00:29:02,715
here above the recording track.

544
00:29:04,180 --> 00:29:08,200
And the CF, it looks
like, started at 0.5

545
00:29:08,200 --> 00:29:10,572
and quickly went
up to 4 and went

546
00:29:10,572 --> 00:29:11,780
higher and higher and higher.

547
00:29:12,910 --> 00:29:16,770
And then went through a
region of the cochlear nucleus

548
00:29:16,770 --> 00:29:18,440
where they didn't
sample any neurons.

549
00:29:20,890 --> 00:29:26,161
And then they went through high
CF's and went back down to low

550
00:29:26,161 --> 00:29:26,660
CF's.

551
00:29:28,040 --> 00:29:28,540
OK?

552
00:29:28,540 --> 00:29:32,680
Because they went into a part
of the ventral cochlear nucleus

553
00:29:32,680 --> 00:29:34,225
here, where the
tonotopic mapping

554
00:29:34,225 --> 00:29:35,350
was a little bit different.

555
00:29:36,670 --> 00:29:40,260
And you can see how
an electrode might

556
00:29:40,260 --> 00:29:43,630
record from a different
projection of frequencies,

557
00:29:43,630 --> 00:29:47,000
if you had the angle right,
going from the dorsal cochlear

558
00:29:47,000 --> 00:29:49,000
nucleus into the ventral
cochlear nucleus.

559
00:29:49,000 --> 00:29:53,140
Because, as you can see, the
branches of the auditory nerve

560
00:29:53,140 --> 00:29:55,610
fibers are quite
complicated here.

561
00:29:55,610 --> 00:29:59,090
They all come up and
they do a bifurcation.

562
00:29:59,090 --> 00:30:02,405
One part goes into
the VCN over here.

563
00:30:03,470 --> 00:30:05,700
Another part goes through
the VCN over here.

564
00:30:05,700 --> 00:30:07,190
And then finally
up into the DCN.

565
00:30:09,650 --> 00:30:12,150
OK, so the tonotopy of
the cochlear nucleus

566
00:30:12,150 --> 00:30:13,800
is quite complicated.

567
00:30:13,800 --> 00:30:16,480
There isn't just
one tonotopic axis.

568
00:30:16,480 --> 00:30:20,810
DCN has one, and in the PVCN
you can have at least one.

569
00:30:21,980 --> 00:30:25,850
But this tonotopic organization
means the cochlear nucleus

570
00:30:25,850 --> 00:30:29,160
neurons are also
tonotopically organized.

571
00:30:29,160 --> 00:30:33,330
So we've transferred
tonotopy from the periphery

572
00:30:33,330 --> 00:30:36,120
through the auditory nerve
and entered the brain

573
00:30:36,120 --> 00:30:37,550
in the cochlear nucleus.

574
00:30:37,550 --> 00:30:41,140
And if you go back to the
block diagram we just had,

575
00:30:41,140 --> 00:30:44,790
cochlear nucleus projects onto
the superior olivary complex

576
00:30:44,790 --> 00:30:47,740
nuclei in an organized fashion.

577
00:30:47,740 --> 00:30:51,375
So you have such tonotopic
mappings in the SOC.

578
00:30:51,375 --> 00:30:53,810
The SOC and cochlear
nucleus project

579
00:30:53,810 --> 00:30:57,170
to the inferior colliculus, and
it's tonotopically organized.

580
00:30:58,510 --> 00:31:00,887
Inferior colliculus
projects to the thalamus

581
00:31:00,887 --> 00:31:03,220
and the medial geniculate,
they have beautiful tonotopy.

582
00:31:03,220 --> 00:31:07,010
The thalamus projects
to the auditory cortex.

583
00:31:08,360 --> 00:31:11,100
And you have at least a
half a dozen cortical fields

584
00:31:11,100 --> 00:31:13,010
that have beautiful
tonotopy organization.

585
00:31:14,260 --> 00:31:19,420
So this tonotopic organization
is a fundamental organizing

586
00:31:19,420 --> 00:31:24,180
pathway for the auditory
central nervous system.

587
00:31:24,180 --> 00:31:26,600
And it means,
basically, that you're

588
00:31:26,600 --> 00:31:31,720
going to process certain
frequencies of sound over here

589
00:31:31,720 --> 00:31:34,100
and other frequencies
of sound over here.

590
00:31:34,100 --> 00:31:36,545
Keep the processing of
different frequencies separate.

591
00:31:38,850 --> 00:31:40,990
And so why would
we want to do that?

592
00:31:40,990 --> 00:31:42,970
Well, it's a matter
of debate, actually.

593
00:31:42,970 --> 00:31:45,480
There's speculation on that.

594
00:31:45,480 --> 00:31:49,400
But as we'll talk about
during sound localization,

595
00:31:49,400 --> 00:31:52,300
you have different
frequency ranges

596
00:31:52,300 --> 00:31:56,530
for the cues that are involved
in timing between the two ears

597
00:31:56,530 --> 00:31:59,420
and level differences
between the two ears.

598
00:31:59,420 --> 00:32:01,350
Some work best at
low frequencies,

599
00:32:01,350 --> 00:32:03,500
and others work best
at high frequencies.

600
00:32:03,500 --> 00:32:05,970
So maybe that is
the idea, that you

601
00:32:05,970 --> 00:32:10,170
want to process those cues
for the location of sound

602
00:32:10,170 --> 00:32:11,550
in different places
in the brain.

603
00:32:13,780 --> 00:32:17,270
So tonotopic organization is
typical of almost all nuclei

604
00:32:17,270 --> 00:32:18,280
in the auditory pathway.

605
00:32:20,770 --> 00:32:22,360
So you could ask
the idea, are there

606
00:32:22,360 --> 00:32:24,570
other mappings in
the other directions?

607
00:32:24,570 --> 00:32:29,330
And it's not clear, in
general, whether there are.

608
00:32:29,330 --> 00:32:32,030
Along the cochlear
nucleus in this dimension

609
00:32:32,030 --> 00:32:36,140
there are different types
of cells that we'll talk to.

610
00:32:36,140 --> 00:32:38,130
But we should
remember that there's

611
00:32:38,130 --> 00:32:41,675
a third dimension coming in
and out of the screen here.

612
00:32:43,440 --> 00:32:45,120
What dimension would that be?

613
00:32:45,120 --> 00:32:47,920
That would be medial- lateral.

614
00:32:47,920 --> 00:32:50,230
So lateral might
be close to you,

615
00:32:50,230 --> 00:32:52,410
and medial would be far away.

616
00:32:52,410 --> 00:32:54,910
So that actually
brings up the idea

617
00:32:54,910 --> 00:32:59,025
that we're looking at
two-dimensional pictures

618
00:32:59,025 --> 00:33:00,870
of three-dimensional structures.

619
00:33:00,870 --> 00:33:05,540
And so I just brought in this
reconstruction, or this model,

620
00:33:05,540 --> 00:33:09,000
of the cochlear nucleus
to remind us of that.

621
00:33:11,080 --> 00:33:13,900
This is the cochlear
nucleus on the left side.

622
00:33:13,900 --> 00:33:16,910
And I believe this
is from a cat.

623
00:33:16,910 --> 00:33:18,750
This is many years old.

624
00:33:18,750 --> 00:33:26,090
And you can see, in black,
some nice little cells here

625
00:33:26,090 --> 00:33:29,585
that are lined up in the layers
of the dorsal cochlear nucleus.

626
00:33:30,900 --> 00:33:33,740
So right here are the layers
of the dorsal cochlear nucleus.

627
00:33:33,740 --> 00:33:36,260
And much of this is
up dorsally here,

628
00:33:36,260 --> 00:33:38,530
so I should explain to
you what plane of section

629
00:33:38,530 --> 00:33:39,570
we're looking at here.

630
00:33:39,570 --> 00:33:41,170
This is the left
cochlear nucleus,

631
00:33:41,170 --> 00:33:42,860
so it would be on my left side.

632
00:33:42,860 --> 00:33:45,500
And now, these are
horizontal sections.

633
00:33:47,040 --> 00:33:47,540
OK?

634
00:33:47,540 --> 00:33:51,520
So for the compass for
horizontal sections,

635
00:33:51,520 --> 00:33:52,860
dorsal is up.

636
00:33:52,860 --> 00:33:53,815
Ventral is down.

637
00:33:55,810 --> 00:33:58,780
Rostral is this way,
forward in the model.

638
00:33:58,780 --> 00:33:59,950
And caudal is back.

639
00:34:01,030 --> 00:34:03,530
Lateral is to the left.

640
00:34:03,530 --> 00:34:05,230
And medial, where
the rest of the brain

641
00:34:05,230 --> 00:34:09,050
is, on the right side, would
be over the right here.

642
00:34:09,050 --> 00:34:12,550
The cochlea is ventral
to the cochlear nucleus.

643
00:34:12,550 --> 00:34:14,590
And this is the auditory
nerve coming up.

644
00:34:16,800 --> 00:34:20,870
And the colors are
meant to represent

645
00:34:20,870 --> 00:34:25,350
the different CF's of
the auditory nerve.

646
00:34:25,350 --> 00:34:29,295
So down here ventrally, we
have the orange, low CF's.

647
00:34:31,460 --> 00:34:33,730
In the middle we
have green, which

648
00:34:33,730 --> 00:34:37,039
is the middle CF's right here.

649
00:34:38,679 --> 00:34:42,810
And very dorsally, which
would be way up in the top

650
00:34:42,810 --> 00:34:44,900
of the screen in the
DCN, you have yellow,

651
00:34:44,900 --> 00:34:46,170
so that's the high CF's.

652
00:34:49,199 --> 00:34:51,560
And so that's the model.

653
00:34:51,560 --> 00:34:54,280
So that's the DCN right here.

654
00:34:54,280 --> 00:34:55,795
And down here would be the VCN.

655
00:34:57,030 --> 00:34:59,630
And so this is a
model where there's

656
00:34:59,630 --> 00:35:04,090
20 or 25 sections or so,
but many have been skipped.

657
00:35:04,090 --> 00:35:05,880
In a typical cochlear
nucleus, if you

658
00:35:05,880 --> 00:35:07,750
were to cut it 50
micrometers you

659
00:35:07,750 --> 00:35:10,560
might have a couple
hundred sections.

660
00:35:12,930 --> 00:35:16,270
So I'll just pass this around.

661
00:35:16,270 --> 00:35:19,970
But there are two other
colors besides the three

662
00:35:19,970 --> 00:35:22,220
that represented the
auditory nerve fibers.

663
00:35:22,220 --> 00:35:25,800
I think-- what did I talk about?

664
00:35:25,800 --> 00:35:29,430
Red, green, and yellow.

665
00:35:29,430 --> 00:35:30,101
Right?

666
00:35:30,101 --> 00:35:31,350
So there are two other colors.

667
00:35:31,350 --> 00:35:35,040
There's orange, and
there's blue on there.

668
00:35:35,040 --> 00:35:36,045
OK, so what's that?

669
00:35:37,700 --> 00:35:43,290
Well, the auditory nerve
is not the only thing

670
00:35:43,290 --> 00:35:46,390
that's providing input
to the cochlear nucleus.

671
00:35:46,390 --> 00:35:49,760
Now you say, oh, this
guy made a mistake,

672
00:35:49,760 --> 00:35:52,410
because on the block
diagram it showed

673
00:35:52,410 --> 00:35:55,270
the only arrow going
into the cochlear nucleus

674
00:35:55,270 --> 00:35:59,100
is from the spiral ganglion,
the auditory nerve.

675
00:35:59,100 --> 00:36:00,740
All these other
arrows are coming out

676
00:36:00,740 --> 00:36:01,820
of the cochlear nucleus.

677
00:36:01,820 --> 00:36:03,547
So what are the
three other colors

678
00:36:03,547 --> 00:36:04,880
that are not the auditory nerve?

679
00:36:04,880 --> 00:36:09,940
Well, this is a diagram of the
so-called "ascending" auditory

680
00:36:09,940 --> 00:36:12,591
system, from low to high.

681
00:36:12,591 --> 00:36:13,090
Right?

682
00:36:13,090 --> 00:36:14,380
The cochlea is the lowest.

683
00:36:15,410 --> 00:36:17,825
The cochlear
nucleus is the next.

684
00:36:17,825 --> 00:36:19,950
And then we went up-- chung,
chung, chung-- all way

685
00:36:19,950 --> 00:36:21,980
to the auditory cortex.

686
00:36:21,980 --> 00:36:25,060
Well, it turns out,
in all sensory systems

687
00:36:25,060 --> 00:36:29,720
and all pathways there are
some direction and information

688
00:36:29,720 --> 00:36:31,810
processing that goes
the opposite way.

689
00:36:31,810 --> 00:36:35,230
Sometimes that's called the
descending auditory system.

690
00:36:35,230 --> 00:36:37,570
So there's, for
example, information

691
00:36:37,570 --> 00:36:41,089
that starts in the
cortex and goes down

692
00:36:41,089 --> 00:36:42,130
to the medial geniculate.

693
00:36:44,100 --> 00:36:46,780
And those other colors
in the cochlear nucleus

694
00:36:46,780 --> 00:36:49,900
represent inputs coming into
the cochlear nucleus that

695
00:36:49,900 --> 00:36:53,060
are coming from higher
centers and going down

696
00:36:53,060 --> 00:36:55,670
to this lowest level of
the auditory pathway.

697
00:36:55,670 --> 00:36:57,585
So those are so-called
"descending" inputs.

698
00:36:59,110 --> 00:37:01,530
And those are not
very well explored.

699
00:37:01,530 --> 00:37:03,900
Obviously, we know what
ascending input is doing.

700
00:37:03,900 --> 00:37:07,790
It's telling the brain there's a
sound and it's processing that.

701
00:37:07,790 --> 00:37:10,560
But why would the brain want
to send information down

702
00:37:10,560 --> 00:37:11,650
to the lower levels?

703
00:37:11,650 --> 00:37:13,461
Well, there are
lots of theories.

704
00:37:13,461 --> 00:37:15,585
We'll talk about them toward
the end of our course.

705
00:37:16,600 --> 00:37:19,930
But it has to do with the
brain controlling inputs coming

706
00:37:19,930 --> 00:37:20,990
into it.

707
00:37:20,990 --> 00:37:23,080
And there even inputs
from the brain going out

708
00:37:23,080 --> 00:37:26,620
as far as the cochlea out
to the auditory periphery.

709
00:37:26,620 --> 00:37:29,205
So those are what those other
colors are in the model.

710
00:37:38,250 --> 00:37:42,630
Now we get to the
part of the lecture

711
00:37:42,630 --> 00:37:46,390
where the cochlear nucleus
becomes very, very complicated.

712
00:37:46,390 --> 00:37:47,985
The anatomical cell types.

713
00:37:49,060 --> 00:37:52,930
And this is where Dorothy
might say to Toto,

714
00:37:52,930 --> 00:37:55,160
"I don't think we're
in Kansas anymore."

715
00:37:55,160 --> 00:37:55,660
OK?

716
00:37:55,660 --> 00:37:58,200
Everything was really
simple in Kansas.

717
00:37:58,200 --> 00:38:00,640
In the auditory nerve-- sorry
if somebody's from Kansas,

718
00:38:00,640 --> 00:38:04,670
here-- but the auditory
nerve is very simple

719
00:38:04,670 --> 00:38:07,305
and the cochlear nucleus
becomes infinitely more complex.

720
00:38:08,460 --> 00:38:14,265
And so here is an example
of how complex it is.

721
00:38:16,580 --> 00:38:20,720
This is the auditory
nerve coming in and making

722
00:38:20,720 --> 00:38:24,640
its bifurcation to go into
the VCN and into the DCN.

723
00:38:26,150 --> 00:38:28,470
And those drawings we
had before were just

724
00:38:28,470 --> 00:38:30,135
sort of stick figures.

725
00:38:31,730 --> 00:38:35,690
And they didn't show all
these nice little endings

726
00:38:35,690 --> 00:38:39,710
onto this whole variety of
cochlear nucleus neurons here.

727
00:38:39,710 --> 00:38:43,130
So how many cochlear
nucleus types are there?

728
00:38:43,130 --> 00:38:44,700
There's about 10 of them.

729
00:38:45,770 --> 00:38:48,225
So that brings me
to today's reading.

730
00:38:49,670 --> 00:38:51,940
I guess I'm developing
this tradition here

731
00:38:51,940 --> 00:38:54,380
of bringing a different
book every lecture

732
00:38:54,380 --> 00:38:55,230
and reading from it.

733
00:38:55,230 --> 00:38:56,900
So this won't take long.

734
00:38:57,960 --> 00:39:01,230
This book is called The
Primary Acoustic Nuclei.

735
00:39:01,230 --> 00:39:04,470
So that's another word
for the cochlear nuclei.

736
00:39:04,470 --> 00:39:08,300
And it's by Raphael
Lorente De No,

737
00:39:08,300 --> 00:39:12,550
who was a Spanish
neuro-anatomist at first,

738
00:39:12,550 --> 00:39:15,545
and did a lot of work
on the cochlear nucleus.

739
00:39:16,570 --> 00:39:20,210
And then during the
Spanish Civil War,

740
00:39:20,210 --> 00:39:22,130
he said, well, I
better get out of here.

741
00:39:22,130 --> 00:39:26,640
So he came to United States
and did a lot of work

742
00:39:26,640 --> 00:39:30,510
on axonal conduction and
physiological measures.

743
00:39:30,510 --> 00:39:33,710
And it says in the
introduction that he put away

744
00:39:33,710 --> 00:39:36,430
his anatomical drawings
ever after maybe

745
00:39:36,430 --> 00:39:38,660
publishing one or two papers.

746
00:39:38,660 --> 00:39:40,890
And he had a whole
big file of them

747
00:39:40,890 --> 00:39:44,200
in a manuscript, ready to
go, and he stuck it away

748
00:39:44,200 --> 00:39:46,140
in a closet for about 30 years.

749
00:39:47,300 --> 00:39:50,110
He dug it out, and
finally published this.

750
00:39:50,110 --> 00:39:53,180
So a lot of this stuff was
done in the 1920s and '30s

751
00:39:53,180 --> 00:39:54,760
and later published.

752
00:39:54,760 --> 00:40:01,860
In fact, the copyright
date for this book is 1981.

753
00:40:01,860 --> 00:40:04,720
And the inscription in
the front of the book

754
00:40:04,720 --> 00:40:08,960
says December
20-something, 1980.

755
00:40:08,960 --> 00:40:11,960
So this is important,
because this

756
00:40:11,960 --> 00:40:15,120
is a book owned by Nelson
Yuan-Sheng Kiang, who

757
00:40:15,120 --> 00:40:18,950
started this course,
904, with Dr. Schiller

758
00:40:18,950 --> 00:40:21,880
back in the 1980s and '90s.

759
00:40:21,880 --> 00:40:24,250
Nelson was very good friends
with the author, here,

760
00:40:24,250 --> 00:40:26,490
and when the author
published the book

761
00:40:26,490 --> 00:40:30,170
he promised Nelson to give
him the very first copy that

762
00:40:30,170 --> 00:40:31,640
came off the printing press.

763
00:40:31,640 --> 00:40:35,192
So this is the first
copy in the original run.

764
00:40:35,192 --> 00:40:36,650
It's not only a
first edition, it's

765
00:40:36,650 --> 00:40:38,710
the first of the first edition.

766
00:40:38,710 --> 00:40:42,440
And the inscription here--
Nelson put December 1980--

767
00:40:42,440 --> 00:40:45,925
is actually a year before--
a month before the copyright

768
00:40:45,925 --> 00:40:46,480
date.

769
00:40:46,480 --> 00:40:50,090
So this really,
really a special book.

770
00:40:50,090 --> 00:40:52,950
So these pictures
here, as you can

771
00:40:52,950 --> 00:40:54,840
see-- you can judge
this book by its cover.

772
00:40:56,630 --> 00:41:00,540
These pictures are the
beautifully complex

773
00:41:00,540 --> 00:41:02,680
incoming auditory
nerve fibers-- which

774
00:41:02,680 --> 00:41:06,430
are drawn in orange here--
bifurcating and showing

775
00:41:06,430 --> 00:41:10,520
the many, many types of endings
on the cochlear nucleus cells.

776
00:41:10,520 --> 00:41:13,810
And that's summarized
by the reading here.

777
00:41:13,810 --> 00:41:16,510
This is the very first
sentence of the book.

778
00:41:16,510 --> 00:41:19,060
"Each neuron in the
ganglion of Corti"--

779
00:41:19,060 --> 00:41:21,820
that's the spiral ganglion--
"gives rise to two nerve

780
00:41:21,820 --> 00:41:25,480
fibers, which, according
to their destination,

781
00:41:25,480 --> 00:41:28,260
are either called peripheral"--
those are the ones that are

782
00:41:28,260 --> 00:41:30,610
contacting the hair cells
we talked about last time--

783
00:41:30,610 --> 00:41:33,170
"or central"-- which we were
talking about right here.

784
00:41:34,860 --> 00:41:37,010
"The peripheral fibers,
at times called dendrites,

785
00:41:37,010 --> 00:41:38,620
penetrate the organ of Corti.

786
00:41:38,620 --> 00:41:40,960
They form sensory
or afferent endings

787
00:41:40,960 --> 00:41:43,130
in contact with the hair cells.

788
00:41:43,130 --> 00:41:48,470
The central fibers, after a
relatively long trajectory

789
00:41:48,470 --> 00:41:53,910
in the cochlear nerve, enter
the primary cochlear nuclei,

790
00:41:53,910 --> 00:41:58,200
where they form elaborate
sets of endings."

791
00:41:58,200 --> 00:42:00,759
OK, that's the reading for
today, and we pass it around.

792
00:42:00,759 --> 00:42:02,175
You can enjoy the
pretty pictures.

793
00:42:03,510 --> 00:42:07,540
So these are the
elaborate sets of endings

794
00:42:07,540 --> 00:42:10,740
on the elaborate variety
of cochlear nucleus cells.

795
00:42:12,620 --> 00:42:15,740
And one of this type
of elaborate endings

796
00:42:15,740 --> 00:42:18,820
is called a large end bulb.

797
00:42:20,030 --> 00:42:21,900
That's the very top one there.

798
00:42:23,320 --> 00:42:29,280
And the other name
for an end bulb--

799
00:42:29,280 --> 00:42:38,335
so, it's large end bulb--
it is the end ball of Held.

800
00:42:41,960 --> 00:42:45,260
Because Held was the early
German neuro-anatomist

801
00:42:45,260 --> 00:42:47,960
who first noticed
this huge ending.

802
00:42:47,960 --> 00:42:53,990
So this ending is so
big that you can hardly

803
00:42:53,990 --> 00:42:57,020
see the cochlear nucleus
cell that it envelops.

804
00:42:58,370 --> 00:43:00,860
Here's another drawing
of the large end bulb,

805
00:43:00,860 --> 00:43:02,220
and there's a scale bar.

806
00:43:03,310 --> 00:43:08,035
The cochlear nucleus cell is
20 micrometers in diameter.

807
00:43:10,401 --> 00:43:10,900
OK?

808
00:43:10,900 --> 00:43:17,770
So you could say that's the
largest ending in the cochlear

809
00:43:17,770 --> 00:43:18,342
nucleus.

810
00:43:18,342 --> 00:43:19,800
Or you could say
that's the largest

811
00:43:19,800 --> 00:43:23,080
ending in the auditory pathway.

812
00:43:23,080 --> 00:43:25,420
Or you could say that's the
largest ending in the brain.

813
00:43:25,420 --> 00:43:28,960
And you'd be right
with all those claims.

814
00:43:28,960 --> 00:43:33,770
So this is a huge ending
from the auditory nerve fiber

815
00:43:33,770 --> 00:43:38,770
onto the cochlear nucleus
cell, way at the tip.

816
00:43:38,770 --> 00:43:45,580
And we can just go back
to the previous drawing.

817
00:43:45,580 --> 00:43:48,650
These are stick figures
where most of the endings

818
00:43:48,650 --> 00:43:51,620
are dropped off for the
purposes of clarity.

819
00:43:51,620 --> 00:43:54,830
But way out of the tip of
the auditory nerve fiber

820
00:43:54,830 --> 00:43:59,310
these end bolts of Held are so
big that you can see them even

821
00:43:59,310 --> 00:44:01,870
with this really
low-magnification picture

822
00:44:01,870 --> 00:44:03,258
of the auditory nerve fibers.

823
00:44:09,480 --> 00:44:15,790
OK And they go onto a particular
type of cochlear nucleus

824
00:44:15,790 --> 00:44:18,535
cell, called a spherical cell.

825
00:44:20,960 --> 00:44:25,270
And in parentheses, that type
of cell is called a bushy cell.

826
00:44:25,270 --> 00:44:26,315
Why are there two names?

827
00:44:27,980 --> 00:44:30,300
Well, this is kind
of a long story,

828
00:44:30,300 --> 00:44:35,255
but there are two main
techniques to look at--

829
00:44:35,255 --> 00:44:38,980
or there were, in
the 1950s and '60s--

830
00:44:38,980 --> 00:44:40,710
to look at cells in the brain.

831
00:44:45,640 --> 00:44:50,265
And one of them was
to use a Nissl stain.

832
00:44:55,125 --> 00:44:57,759
You can cut your
section of the brain,

833
00:44:57,759 --> 00:44:59,300
cut your section of
cochlear nucleus,

834
00:44:59,300 --> 00:45:01,560
put your Nissl
stain on it, and you

835
00:45:01,560 --> 00:45:04,800
can see very beautiful
staining of all the neurons

836
00:45:04,800 --> 00:45:06,450
in the cochlear nucleus.

837
00:45:06,450 --> 00:45:07,670
Some of them look round.

838
00:45:10,680 --> 00:45:12,280
The central nucleus.

839
00:45:12,280 --> 00:45:15,970
And they were called spherical
cells because they're so nice

840
00:45:15,970 --> 00:45:16,470
and round.

841
00:45:20,550 --> 00:45:29,840
And this work was done by a
pioneering neuroscientist who

842
00:45:29,840 --> 00:45:32,970
everybody before-- didn't draw
this very well-- everybody

843
00:45:32,970 --> 00:45:35,630
before thought all the
cochlear nucleus cells just

844
00:45:35,630 --> 00:45:36,990
look like one type.

845
00:45:36,990 --> 00:45:38,520
They look about the same.

846
00:45:38,520 --> 00:45:45,490
This neuroscientist, whose
name is Kirsten Osen,

847
00:45:45,490 --> 00:45:47,489
was the first
person in the 1950s

848
00:45:47,489 --> 00:45:49,280
to look at sections of
the cochlear nucleus

849
00:45:49,280 --> 00:45:52,900
and say, oh, those actually
don't look exactly the same!

850
00:45:52,900 --> 00:45:53,730
Some are spherical.

851
00:45:55,400 --> 00:45:57,543
Some look like octopus.

852
00:45:59,130 --> 00:46:03,910
Here's a cell Kirsten called
the octopus cell, because it

853
00:46:03,910 --> 00:46:07,770
was sort of eccentric, and
these little appendages

854
00:46:07,770 --> 00:46:12,120
coming off of it-- which were
the dendrites-- all came off

855
00:46:12,120 --> 00:46:14,611
from one side, like the
tentacles of the octopus come

856
00:46:14,611 --> 00:46:15,985
off from one side
of the octopus.

857
00:46:17,360 --> 00:46:19,550
And this big nucleus,
right in the center, to her

858
00:46:19,550 --> 00:46:21,211
looked like the
eye of the octopus.

859
00:46:21,211 --> 00:46:21,710
Right?

860
00:46:24,790 --> 00:46:29,600
Some of the cochlear nucleus
cells were multipolar.

861
00:46:29,600 --> 00:46:33,430
Here's one called the giant
multipolar cell of the DCN.

862
00:46:33,430 --> 00:46:37,564
And a pole just means that
something came off the cell,

863
00:46:37,564 --> 00:46:38,730
and those are the dendrites.

864
00:46:40,760 --> 00:46:41,580
OK?

865
00:46:41,580 --> 00:46:45,990
The Nissl stain doesn't stay
in the dendrites very well.

866
00:46:45,990 --> 00:46:47,700
If it did, the whole
cochlear nucleus

867
00:46:47,700 --> 00:46:50,210
would be black because there
are dendrites everywhere.

868
00:46:50,210 --> 00:46:52,560
But it stains the
cell body very nicely.

869
00:46:52,560 --> 00:46:55,420
So what does the
Nissl stain stain?

870
00:46:55,420 --> 00:47:02,880
It stains DNA, RNA,
and some protein.

871
00:47:06,450 --> 00:47:08,830
Which are, of
course, found mostly

872
00:47:08,830 --> 00:47:11,180
in the cell body of the cell.

873
00:47:11,180 --> 00:47:14,330
So it gives you a good look
at the cell body of the cell.

874
00:47:14,330 --> 00:47:16,030
Not a good look
at the dendrites,

875
00:47:16,030 --> 00:47:18,980
because they don't have
as much DNA and RNA.

876
00:47:18,980 --> 00:47:22,220
And hardly any look at the axon.

877
00:47:22,220 --> 00:47:23,780
The axons are invisible.

878
00:47:23,780 --> 00:47:26,140
But for classifying
cells, it's really great,

879
00:47:26,140 --> 00:47:28,499
because you have every
single cell stained,

880
00:47:28,499 --> 00:47:29,540
and you can look at them.

881
00:47:30,870 --> 00:47:33,045
Here's a cell called
the globular cell.

882
00:47:34,430 --> 00:47:37,100
And that is a little bit
like a spherical cell,

883
00:47:37,100 --> 00:47:38,930
but it's more oblong.

884
00:47:38,930 --> 00:47:40,850
Here are some other
multipolar cells.

885
00:47:40,850 --> 00:47:43,370
Here's a cell called
the pyramidal cell.

886
00:47:43,370 --> 00:47:46,240
So I should have said
that the Nissl designation

887
00:47:46,240 --> 00:47:49,060
of these cells is given
non-parenthetically.

888
00:47:50,240 --> 00:47:50,740
OK?

889
00:47:50,740 --> 00:48:00,320
So you have, by Nissl, spherical
cells, multipolar cells--

890
00:48:00,320 --> 00:48:03,550
here's another kind of
multipolar cell-- globular

891
00:48:03,550 --> 00:48:07,930
cell, octopus cell,
and pyramidal cells.

892
00:48:07,930 --> 00:48:09,950
So those are the cells I
would like you to know.

893
00:48:11,260 --> 00:48:12,930
Those of the important
types of cells.

894
00:48:15,360 --> 00:48:16,410
Let me write that down.

895
00:48:20,400 --> 00:48:24,040
The view graph is
a little bit more--

896
00:48:24,040 --> 00:48:28,494
it makes more distinctions than
I care to make for this class.

897
00:48:28,494 --> 00:48:29,410
So you have spherical.

898
00:48:33,530 --> 00:48:36,770
These are cells in
the cochlear nucleus.

899
00:48:38,630 --> 00:48:39,790
Spherical cells.

900
00:48:39,790 --> 00:48:41,455
You have multipolar cells.

901
00:48:44,795 --> 00:48:45,545
You have globular.

902
00:48:49,056 --> 00:48:50,123
You have octopus.

903
00:48:53,467 --> 00:48:54,425
And you have pyramidal.

904
00:48:59,770 --> 00:49:00,530
Right?

905
00:49:00,530 --> 00:49:04,560
I mean, since scientists
are classifiers,

906
00:49:04,560 --> 00:49:06,970
you have sub-types
of each of these.

907
00:49:06,970 --> 00:49:09,780
OK, you could just
keep sub-typing

908
00:49:09,780 --> 00:49:10,950
as much as you want to.

909
00:49:10,950 --> 00:49:12,670
But these are the
main types that we

910
00:49:12,670 --> 00:49:15,780
want to pay attention
to for our course.

911
00:49:15,780 --> 00:49:17,480
And these are Nissl stained.

912
00:49:22,890 --> 00:49:25,540
Now along comes another
person and wants

913
00:49:25,540 --> 00:49:28,750
to make his mark on
science, and says,

914
00:49:28,750 --> 00:49:30,980
I'm going to use a
different type of stain

915
00:49:30,980 --> 00:49:33,290
and look at the cochlear
nucleus in a different way.

916
00:49:35,410 --> 00:49:40,420
And his name was-- his
name is-- Kent Morest.

917
00:49:45,510 --> 00:49:48,477
And he worked at Harvard
for quite a while,

918
00:49:48,477 --> 00:49:50,435
and then went to the
University of Connecticut.

919
00:49:51,840 --> 00:49:56,230
And so his stain that he used
was called the Golgi stain.

920
00:50:02,010 --> 00:50:04,240
And many of the pictures
in the book I passed around

921
00:50:04,240 --> 00:50:06,230
were Golgi stains of fibers.

922
00:50:06,230 --> 00:50:09,420
He wanted to look at Golgi
stains of cochlear nucleus

923
00:50:09,420 --> 00:50:12,530
cells and compare them
to the Nissl stain.

924
00:50:12,530 --> 00:50:14,570
So what does the Golgi stain do?

925
00:50:14,570 --> 00:50:15,560
Does anybody know?

926
00:50:15,560 --> 00:50:16,880
Or who was Golgi?

927
00:50:19,620 --> 00:50:20,120
Yes.

928
00:50:21,542 --> 00:50:23,912
AUDIENCE: Golgi
stains the whole cell,

929
00:50:23,912 --> 00:50:26,440
but it doesn't stain all cells.

930
00:50:26,440 --> 00:50:27,570
PROFESSOR: That's correct.

931
00:50:27,570 --> 00:50:30,260
In fact, in the
ultimate case, you

932
00:50:30,260 --> 00:50:32,470
can put your brain
in the Golgi solution

933
00:50:32,470 --> 00:50:34,200
and come back a
couple months later

934
00:50:34,200 --> 00:50:37,280
and you could just have one
neuron in the entire brain

935
00:50:37,280 --> 00:50:37,780
stained.

936
00:50:39,430 --> 00:50:42,900
But the good thing about
that is that the neuron cell

937
00:50:42,900 --> 00:50:48,280
body, it's dendrites, and
a good portion of its axon

938
00:50:48,280 --> 00:50:50,825
pick up the stain and
they stain it jet black.

939
00:50:52,670 --> 00:50:58,670
So the Golgi stain
takes a spherical cell

940
00:50:58,670 --> 00:51:03,540
and transforms it into something
that's really beautiful.

941
00:51:03,540 --> 00:51:06,380
The cell body is
completely filled.

942
00:51:06,380 --> 00:51:06,910
It's black.

943
00:51:06,910 --> 00:51:08,275
I should be using black.

944
00:51:09,452 --> 00:51:10,835
This is a black stain.

945
00:51:14,680 --> 00:51:17,640
And you can see, coming
from the spherical cell, one

946
00:51:17,640 --> 00:51:18,600
major dendrite.

947
00:51:18,600 --> 00:51:19,500
It's a big one.

948
00:51:20,760 --> 00:51:23,310
And it, very close
to the cell body,

949
00:51:23,310 --> 00:51:26,550
ramifies into thousands
of little bitty dendrites.

950
00:51:29,000 --> 00:51:29,710
Like this.

951
00:51:31,170 --> 00:51:34,970
Where this scale might
be 20 micrometers.

952
00:51:34,970 --> 00:51:38,570
And so the dendrite is sticking
very close to the cell body.

953
00:51:40,560 --> 00:51:42,770
To Kent Morest, this
looked like-- he

954
00:51:42,770 --> 00:51:45,270
must've been planting
stuff in his yard,

955
00:51:45,270 --> 00:51:47,430
because this looked like a bush.

956
00:51:47,430 --> 00:51:50,310
You go to the nursery,
and you pick up a bush.

957
00:51:50,310 --> 00:51:51,690
Here's the top of the bush.

958
00:51:51,690 --> 00:51:52,440
This is the trunk.

959
00:51:53,590 --> 00:51:57,990
And this is the root ball
the nursery people bundle up

960
00:51:57,990 --> 00:52:00,070
for you, or this is in a pot.

961
00:52:00,070 --> 00:52:01,630
So this looked like a bush.

962
00:52:01,630 --> 00:52:04,390
So he called it a bushy cell.

963
00:52:08,470 --> 00:52:11,880
And so in parentheses
on the view graph

964
00:52:11,880 --> 00:52:15,940
there are the designations
that are given to these cells

965
00:52:15,940 --> 00:52:19,010
in the Golgi stain, which
is all in parentheses there.

966
00:52:20,220 --> 00:52:22,100
It looks completely
different, because you're

967
00:52:22,100 --> 00:52:24,750
staining different
parts of the cell.

968
00:52:24,750 --> 00:52:26,275
So let's make our little chart.

969
00:52:28,110 --> 00:52:36,392
Spherical cells in the
Golgi stain are called bush.

970
00:52:36,392 --> 00:52:37,770
We'll put these in parentheses.

971
00:52:40,296 --> 00:52:40,795
Bushy cells.

972
00:52:43,100 --> 00:52:51,230
Multipolar cells are usually
called stellate because now,

973
00:52:51,230 --> 00:52:55,590
instead of just the beginning
of the dendrite coming off,

974
00:52:55,590 --> 00:52:58,080
you have long
expanses of dendrites

975
00:52:58,080 --> 00:53:01,470
that go for 500
micrometers from the cell.

976
00:53:01,470 --> 00:53:03,700
They can go across
the cochlear nucleus.

977
00:53:03,700 --> 00:53:06,330
And they look like
beautiful, twinkling stars.

978
00:53:06,330 --> 00:53:07,880
At least they did
to Kent Morest.

979
00:53:09,430 --> 00:53:15,930
Globular cells look exactly like
spherical cells in the Golgi

980
00:53:15,930 --> 00:53:18,780
stain, and they were
given the same name.

981
00:53:18,780 --> 00:53:19,600
Bushy cells.

982
00:53:22,130 --> 00:53:26,920
Octopus cells are so
clear, what they are,

983
00:53:26,920 --> 00:53:28,155
they're given the same name.

984
00:53:29,190 --> 00:53:31,260
Pyramidal cells are
sometimes called fusiform.

985
00:53:34,902 --> 00:53:36,485
Fusiform means sort
of spindle-shaped.

986
00:53:38,400 --> 00:53:40,920
They just look different
in the Golgi stain.

987
00:53:43,120 --> 00:53:45,650
Now, this is sort of old stuff.

988
00:53:45,650 --> 00:53:51,180
And so now, when somebody talks
about a certain type of cell

989
00:53:51,180 --> 00:53:54,970
in the cochlear nucleus, they
use a hybrid terminology.

990
00:53:54,970 --> 00:53:59,690
They'll say, "I was recording
from spherical bushy cells."

991
00:53:59,690 --> 00:54:01,630
So they use both names.

992
00:54:01,630 --> 00:54:06,250
Or, "I think I was recording
from globular bushy cells."

993
00:54:06,250 --> 00:54:09,830
Or, "My study is on
multipolar stellate cells."

994
00:54:09,830 --> 00:54:10,330
OK?

995
00:54:11,690 --> 00:54:16,030
Or, "These cells in the DCN
are pyramidal fusiform cells."

996
00:54:16,030 --> 00:54:19,780
So they use a hybrid
terminology and they

997
00:54:19,780 --> 00:54:22,298
concatenate, if
you will, the two.

998
00:54:28,790 --> 00:54:31,740
OK, so these are the
cell types, if you will.

999
00:54:33,680 --> 00:54:39,410
Now let's go into the
cochlear nucleus and record,

1000
00:54:39,410 --> 00:54:42,580
with recording electrodes,
a sample not from fibers

1001
00:54:42,580 --> 00:54:43,635
but from cell bodies.

1002
00:54:45,020 --> 00:54:46,020
And see what we get.

1003
00:54:48,930 --> 00:54:50,300
I think that's what's next here.

1004
00:54:50,300 --> 00:54:51,010
Yes.

1005
00:54:51,010 --> 00:54:51,510
OK.

1006
00:54:54,090 --> 00:54:55,970
Where are these data from?

1007
00:54:55,970 --> 00:54:57,320
From Pfeiffer.

1008
00:54:57,320 --> 00:55:01,450
So Pfeiffer worked with Nelson
Kiang, who owns that book.

1009
00:55:01,450 --> 00:55:05,790
And they worked at MIT during
the 19-late-50s and 1960s.

1010
00:55:05,790 --> 00:55:09,980
And these were, again, some
of the first applications

1011
00:55:09,980 --> 00:55:11,600
of computers to neuroscience.

1012
00:55:12,950 --> 00:55:15,640
They said, well, what we
want to do from these cells

1013
00:55:15,640 --> 00:55:18,530
to classify them--
well, maybe they

1014
00:55:18,530 --> 00:55:21,330
used a whole bunch of different
schemes and all of them

1015
00:55:21,330 --> 00:55:23,520
didn't work out very
well, except this one.

1016
00:55:24,741 --> 00:55:26,500
They said, for this
one, what we're

1017
00:55:26,500 --> 00:55:29,760
going to look at for these
units in the cochlear nucleus,

1018
00:55:29,760 --> 00:55:32,960
is not the tuning curves,
not their responses to this

1019
00:55:32,960 --> 00:55:33,780
or that.

1020
00:55:33,780 --> 00:55:37,660
We're going to look,
very shortly after we

1021
00:55:37,660 --> 00:55:40,690
turn the tone burst
on-- the tone burst

1022
00:55:40,690 --> 00:55:42,980
is the stimulation--
we're going to look

1023
00:55:42,980 --> 00:55:44,490
at the timing of spikes.

1024
00:55:46,090 --> 00:55:49,020
And so these are in the order
of millisecond intervals.

1025
00:55:49,020 --> 00:55:53,920
In fact, some of the bins have
width less than a millisecond.

1026
00:55:53,920 --> 00:55:54,420
OK?

1027
00:55:54,420 --> 00:55:57,960
They want to look very precisely
at the time pattern of spikes

1028
00:55:57,960 --> 00:55:59,900
after you turn a sound on.

1029
00:56:01,370 --> 00:56:02,380
So tone burst.

1030
00:56:02,380 --> 00:56:03,447
What is a tone burst?

1031
00:56:03,447 --> 00:56:04,280
I've used that term.

1032
00:56:04,280 --> 00:56:09,010
So it's just-- I think we had,
earlier in the course, a tone

1033
00:56:09,010 --> 00:56:09,580
pip.

1034
00:56:09,580 --> 00:56:18,590
So a tone burst is just
sounds that to do this.

1035
00:56:18,590 --> 00:56:19,920
So it's a burst of tone.

1036
00:56:21,290 --> 00:56:22,505
Burst of a pure tone.

1037
00:56:22,505 --> 00:56:25,600
And it looks like the duration
here is 25 milliseconds.

1038
00:56:32,951 --> 00:56:33,450
OK.

1039
00:56:33,450 --> 00:56:35,840
And all these neurons
are tuned, so you

1040
00:56:35,840 --> 00:56:42,160
want to use your sound
frequency at the CF.

1041
00:56:42,160 --> 00:56:44,636
So within the tone,
versus the CF.

1042
00:56:45,944 --> 00:56:49,140
You want to get spikes
coming from the neurons.

1043
00:56:49,140 --> 00:56:50,320
So you want to be at CF.

1044
00:56:50,320 --> 00:56:51,950
You want to above threshold.

1045
00:56:52,892 --> 00:56:54,600
You turn your tone
burst on, and then you

1046
00:56:54,600 --> 00:56:57,460
have your computer
look at the spikes

1047
00:56:57,460 --> 00:56:59,600
and say when they occur in time.

1048
00:57:01,480 --> 00:57:04,420
OK, so this is pretty important.

1049
00:57:04,420 --> 00:57:05,785
So I have a pointer here.

1050
00:57:10,120 --> 00:57:13,070
So how did this experiment work?

1051
00:57:13,070 --> 00:57:19,340
Well, here's data from one, two,
three, four different cochlear

1052
00:57:19,340 --> 00:57:20,105
nucleus neurons.

1053
00:57:21,630 --> 00:57:26,110
And from each neuron there
are two types of displays.

1054
00:57:26,110 --> 00:57:29,960
This display on the top is
called a dot raster display.

1055
00:57:31,090 --> 00:57:35,690
And each little dot
signifies the time

1056
00:57:35,690 --> 00:57:39,060
of occurrence of a
spike, an impulse,

1057
00:57:39,060 --> 00:57:40,510
from the recorded neuron.

1058
00:57:41,660 --> 00:57:46,200
And on the Y-- down the
X-axis is the time axis.

1059
00:57:46,200 --> 00:57:49,920
So starting at zero is when
the tone burst went on.

1060
00:57:49,920 --> 00:57:54,450
Tone burst goes off at, looks
like, 40 milliseconds here.

1061
00:57:54,450 --> 00:57:56,700
And then there's an off
time when there's just

1062
00:57:56,700 --> 00:57:58,640
silence for the last
40 milliseconds.

1063
00:58:00,540 --> 00:58:02,480
And the important
thing about this

1064
00:58:02,480 --> 00:58:05,200
is that this column
here shows you

1065
00:58:05,200 --> 00:58:08,540
that there wasn't just
one tone burst presented,

1066
00:58:08,540 --> 00:58:10,140
but there were many.

1067
00:58:10,140 --> 00:58:15,900
And these experiments can use
600 or even 1,000 tone bursts.

1068
00:58:15,900 --> 00:58:18,850
Each time the
stimulus is turned on,

1069
00:58:18,850 --> 00:58:20,420
you give it a stimulus number.

1070
00:58:20,420 --> 00:58:23,870
So the very first tone burst
is stimulus number one.

1071
00:58:23,870 --> 00:58:27,040
And that's the first
dot raster here.

1072
00:58:27,040 --> 00:58:30,460
And the neuron fired a dozen
or so action potentials

1073
00:58:30,460 --> 00:58:32,086
at those times.

1074
00:58:32,086 --> 00:58:34,210
And then it stopped firing,
except for a little bit

1075
00:58:34,210 --> 00:58:35,290
of spontaneous activity.

1076
00:58:36,480 --> 00:58:38,725
Then tone burst number
two was presented.

1077
00:58:39,850 --> 00:58:42,120
And the neuron's dot
raster for number two

1078
00:58:42,120 --> 00:58:43,665
is the next line down.

1079
00:58:45,925 --> 00:58:47,550
Then you go through
your silent period,

1080
00:58:47,550 --> 00:58:48,758
and go back to the beginning.

1081
00:58:48,758 --> 00:58:51,110
Tone burst number
three was presented.

1082
00:58:51,110 --> 00:58:53,505
And you get this
pattern of spikes.

1083
00:58:53,505 --> 00:58:54,770
It's a little bit different.

1084
00:58:54,770 --> 00:58:57,110
Each one looks like it's
a little bit different.

1085
00:58:57,110 --> 00:58:58,783
Down here is tone
verse number 15.

1086
00:59:00,530 --> 00:59:01,030
OK?

1087
00:59:01,030 --> 00:59:03,217
And you get that dot
raster of spikes.

1088
00:59:03,217 --> 00:59:05,425
And then you go through your
hundreds of tone bursts.

1089
00:59:05,425 --> 00:59:10,060
And this might be tone burst
number 999 down at the bottom,

1090
00:59:10,060 --> 00:59:11,300
and you get that raster.

1091
00:59:13,150 --> 00:59:15,145
And you keep track
of all those dots.

1092
00:59:16,970 --> 00:59:20,310
And you have the computer
put them into bins here.

1093
00:59:21,460 --> 00:59:25,410
And this histogram
shows you the bins

1094
00:59:25,410 --> 00:59:29,440
where the number of action
potentials is along the Y-axis

1095
00:59:29,440 --> 00:59:29,940
now.

1096
00:59:31,270 --> 00:59:34,490
And the X-axis is
still displaying time.

1097
00:59:34,490 --> 00:59:38,635
And this horizontal line shows
you when the tone burst was on.

1098
00:59:40,550 --> 00:59:47,780
So this type of histogram, which
is compiled from many stimulus

1099
00:59:47,780 --> 00:59:50,550
presentations and
many dot rasters,

1100
00:59:50,550 --> 00:59:53,393
are sometimes called
the PST histograms.

1101
00:59:55,290 --> 01:00:12,160
And that stands for post-
or peristimulus time.

1102
01:00:13,500 --> 01:00:15,680
Obviously, it's
a time histogram.

1103
01:00:15,680 --> 01:00:17,610
Obviously, there's a stimulus.

1104
01:00:17,610 --> 01:00:18,880
Why is this a post?

1105
01:00:18,880 --> 01:00:21,110
Well, the terminology
started up when

1106
01:00:21,110 --> 01:00:24,150
you, instead of having a long
tone burst, have a click.

1107
01:00:24,150 --> 01:00:26,526
So that when the click goes
on, it goes off real quickly

1108
01:00:26,526 --> 01:00:27,900
and everything is
post- stimulus.

1109
01:00:28,930 --> 01:00:31,870
So it's really, in
this case, a peri--

1110
01:00:31,870 --> 01:00:34,390
around the stimulus--
time histogram.

1111
01:00:34,390 --> 01:00:36,560
Does everybody
explain-- Does everybody

1112
01:00:36,560 --> 01:00:39,040
know what I'm
talking about here?

1113
01:00:39,040 --> 01:00:40,580
About what this display is?

1114
01:00:40,580 --> 01:00:41,470
OK.

1115
01:00:41,470 --> 01:00:45,120
So you can think
of this PST, then,

1116
01:00:45,120 --> 01:00:47,550
as reflecting the
average firing rate

1117
01:00:47,550 --> 01:00:50,790
as a function of
time for the neuron.

1118
01:00:50,790 --> 01:00:54,230
And quickly, you're not turning
the tone on for many seconds.

1119
01:00:54,230 --> 01:00:56,170
It's within a few milliseconds.

1120
01:00:56,170 --> 01:00:59,960
Within the first 40
milliseconds of when

1121
01:00:59,960 --> 01:01:01,410
the tone burst is turned on.

1122
01:01:01,410 --> 01:01:04,355
And it's an average response.

1123
01:01:07,070 --> 01:01:09,550
And here's data from one unit.

1124
01:01:09,550 --> 01:01:10,990
Here's data from another unit.

1125
01:01:10,990 --> 01:01:13,280
Now, even in the
dot raster you don't

1126
01:01:13,280 --> 01:01:15,710
need to worry about
averaging here.

1127
01:01:15,710 --> 01:01:18,190
This type of firing
is fundamentally

1128
01:01:18,190 --> 01:01:22,340
different from the type of
firing we just talked about.

1129
01:01:22,340 --> 01:01:24,470
It looked like on
every single tone burst

1130
01:01:24,470 --> 01:01:27,520
there was a kind of a
different firing pattern.

1131
01:01:27,520 --> 01:01:28,800
Sort of random.

1132
01:01:28,800 --> 01:01:33,200
As if you took your
pepper shaker and just

1133
01:01:33,200 --> 01:01:35,270
spread out some salt
and pepper here.

1134
01:01:35,270 --> 01:01:38,240
There wasn't a real
organization to it.

1135
01:01:38,240 --> 01:01:41,100
Sure, there's a higher
firing during the tone burst,

1136
01:01:41,100 --> 01:01:42,830
after a little latency.

1137
01:01:42,830 --> 01:01:45,600
But over here, there's a
real nice pattern to it.

1138
01:01:46,950 --> 01:01:49,760
And it looks like in this unit,
which was called the Chopper

1139
01:01:49,760 --> 01:01:54,460
unit, even from the very
first stimulus number, it went

1140
01:01:54,460 --> 01:01:59,960
"pop, pop, pop, pop, pop, pop,
pop" if you slowed way down.

1141
01:01:59,960 --> 01:02:01,150
Same for the second.

1142
01:02:01,150 --> 01:02:02,150
Same for the 15th.

1143
01:02:02,150 --> 01:02:03,163
Same for the 999th.

1144
01:02:04,800 --> 01:02:09,130
This Chopper unit has a
very organized and precise

1145
01:02:09,130 --> 01:02:10,680
temporal pattern of firing.

1146
01:02:11,790 --> 01:02:16,070
When you do the averaging
and get the PST,

1147
01:02:16,070 --> 01:02:20,410
you can see this very nice
so-called chopping peaks

1148
01:02:20,410 --> 01:02:25,140
in the PST histogram
for this Chopper unit

1149
01:02:25,140 --> 01:02:27,560
as compared to this other unit.

1150
01:02:27,560 --> 01:02:30,770
Here is a unit where you can
also see, from the dot raster

1151
01:02:30,770 --> 01:02:35,340
display, that this unit
fired a spike and took

1152
01:02:35,340 --> 01:02:38,410
a substantial pause--
which gives it

1153
01:02:38,410 --> 01:02:43,040
a name, the Pauser unit--
before it started firing again.

1154
01:02:43,040 --> 01:02:46,620
And here is the PST histogram
from a so-called Pauser

1155
01:02:46,620 --> 01:02:49,880
unit, where the pause
is a substantial pause.

1156
01:02:49,880 --> 01:02:51,190
It's 10 milliseconds or so.

1157
01:02:52,440 --> 01:02:55,560
And finally, here's a unit
called an Onset unit, which

1158
01:02:55,560 --> 01:02:59,020
fires only one spike
at the onset of each

1159
01:02:59,020 --> 01:03:01,920
and every sound stimulus.

1160
01:03:01,920 --> 01:03:03,280
Each and every tone burst.

1161
01:03:03,280 --> 01:03:05,870
And obviously gets
its name, Onset unit.

1162
01:03:07,170 --> 01:03:08,970
Now, let's go back
to this first unit.

1163
01:03:08,970 --> 01:03:09,840
Why?

1164
01:03:09,840 --> 01:03:11,350
I glossed over the name.

1165
01:03:11,350 --> 01:03:13,900
Why is it called the
Primarylike unit?

1166
01:03:14,950 --> 01:03:19,640
Well, if you go and record from
primary auditory nerve fibers--

1167
01:03:19,640 --> 01:03:21,720
and where does that
terminology come from?

1168
01:03:21,720 --> 01:03:24,520
Well, in the auditory system
you have the hair cell,

1169
01:03:24,520 --> 01:03:27,630
you have the nerve
fiber-- so the nerve fiber

1170
01:03:27,630 --> 01:03:31,070
is the very first,
or primary neuron.

1171
01:03:31,070 --> 01:03:32,770
Then you go into
the cochlear nucleus

1172
01:03:32,770 --> 01:03:34,490
and you have the
secondary neuron.

1173
01:03:34,490 --> 01:03:36,830
So really, this is
a secondary neuron.

1174
01:03:36,830 --> 01:03:38,970
But the pattern,
the PST pattern,

1175
01:03:38,970 --> 01:03:41,840
that you get in some of these
cochlear nucleus neurons

1176
01:03:41,840 --> 01:03:44,880
looks just like primary
auditory nerve fibers.

1177
01:03:45,980 --> 01:03:48,930
Except they have a little
bit longer in latency.

1178
01:03:48,930 --> 01:03:51,610
So this one is called
Primarylike unit.

1179
01:03:53,180 --> 01:03:54,400
It's not a primary.

1180
01:03:54,400 --> 01:03:56,377
It's a secondary
neuron, but it's like.

1181
01:03:56,377 --> 01:03:57,210
Primarylike pattern.

1182
01:03:59,020 --> 01:03:59,520
OK.

1183
01:03:59,520 --> 01:04:03,710
So in the cochlear nucleus,
you have these different types

1184
01:04:03,710 --> 01:04:04,930
of firing patterns.

1185
01:04:06,950 --> 01:04:10,212
And let's make a list of them.

1186
01:04:14,000 --> 01:04:15,630
Maybe I'll make
the list over here.

1187
01:04:23,940 --> 01:04:25,520
So these are the unit types.

1188
01:04:32,181 --> 01:04:32,680
Primarylike.

1189
01:04:38,375 --> 01:04:38,875
Chopper.

1190
01:04:43,695 --> 01:04:44,195
Pauser.

1191
01:04:47,215 --> 01:04:48,205
And Onset.

1192
01:04:51,680 --> 01:04:53,300
Those are the four basic types.

1193
01:04:53,300 --> 01:04:55,910
Now, again, scientists
are classifiers,

1194
01:04:55,910 --> 01:04:59,770
so you-- if you read the
literature-- you will find

1195
01:04:59,770 --> 01:05:03,060
some units called
Primarylike with notch.

1196
01:05:04,900 --> 01:05:09,690
So those are Primarylike units,
but right after the first peak

1197
01:05:09,690 --> 01:05:11,310
they have a little notch.

1198
01:05:11,310 --> 01:05:13,040
Don't worry about that.

1199
01:05:13,040 --> 01:05:14,466
It's basically a
Primarylike unit.

1200
01:05:22,090 --> 01:05:27,730
Now, we have two interesting
classification schemes here.

1201
01:05:27,730 --> 01:05:30,270
One is how the unit
responds to sound.

1202
01:05:32,250 --> 01:05:34,755
One is how the neuron
looks in the microscope.

1203
01:05:36,310 --> 01:05:39,010
Can we make a correspondence
between the two?

1204
01:05:39,010 --> 01:05:42,450
Now, one possible
outcome could be,

1205
01:05:42,450 --> 01:05:43,860
"There is no correspondence."

1206
01:05:43,860 --> 01:05:44,780
Right?

1207
01:05:44,780 --> 01:05:47,320
Could be that spherical
cells can produce

1208
01:05:47,320 --> 01:05:49,139
any of those kind of
responses to sound.

1209
01:05:49,139 --> 01:05:51,430
Well, obviously, I wouldn't
be devoting a whole lecture

1210
01:05:51,430 --> 01:05:53,970
to this if that
were the outcome.

1211
01:05:53,970 --> 01:05:56,920
And in fact, the
cochlear nucleus

1212
01:05:56,920 --> 01:06:01,830
is a place where we can really
correlate anatomy of the cells

1213
01:06:01,830 --> 01:06:04,340
with their physiological
unit types.

1214
01:06:05,450 --> 01:06:06,510
And how is that done?

1215
01:06:06,510 --> 01:06:08,500
Well, there are
several different ways.

1216
01:06:10,490 --> 01:06:13,720
And this graph
shows you one way.

1217
01:06:13,720 --> 01:06:17,460
That is by going to different
parts of the cochlear nucleus.

1218
01:06:18,550 --> 01:06:22,910
Where the cell types are
not equally distributed,

1219
01:06:22,910 --> 01:06:25,565
you find that the unit types
are not equally distributed.

1220
01:06:27,430 --> 01:06:30,295
And this works very well for
certain areas of the cochlear

1221
01:06:30,295 --> 01:06:30,795
nucleus.

1222
01:06:31,850 --> 01:06:35,000
For example, this area
right here called OC.

1223
01:06:36,920 --> 01:06:39,855
That's the area called
the octopus cell area.

1224
01:06:40,960 --> 01:06:42,130
What's found there?

1225
01:06:43,280 --> 01:06:46,090
That's basically where you
have all the octopus cells.

1226
01:06:49,010 --> 01:06:51,950
They're found in a particular
part of the ventral cochlear

1227
01:06:51,950 --> 01:06:52,710
nucleus.

1228
01:06:52,710 --> 01:06:55,055
OK, let's go record there
with our electrodes.

1229
01:06:56,290 --> 01:06:59,520
And what kind of PST
pattern do you get there?

1230
01:06:59,520 --> 01:07:01,442
Well these are numbered types.

1231
01:07:01,442 --> 01:07:02,775
Where number one is Primarylike.

1232
01:07:04,440 --> 01:07:05,590
Number two is Chopper.

1233
01:07:06,640 --> 01:07:10,990
And these are sub-types of
Onset-- three, four, and five.

1234
01:07:10,990 --> 01:07:12,300
And number six is Pauser.

1235
01:07:13,450 --> 01:07:18,460
In the octopus cell area
you get Onset responses.

1236
01:07:22,520 --> 01:07:24,330
OK, so let's start
drawing some lines.

1237
01:07:28,310 --> 01:07:33,110
Octopus cells then
produce Onset patterns.

1238
01:07:35,330 --> 01:07:37,940
Now, that's true.

1239
01:07:37,940 --> 01:07:40,480
You can really sink
your hat on it.

1240
01:07:40,480 --> 01:07:43,300
How about going the other way?

1241
01:07:43,300 --> 01:07:48,090
Do you always get Onset response
from just octopus cells?

1242
01:07:48,090 --> 01:07:50,350
Or how about some of
these other types?

1243
01:07:50,350 --> 01:07:56,210
Well, going the other way, you
do have a few multipolar cells

1244
01:07:56,210 --> 01:07:59,950
that can produce the Onset type.

1245
01:07:59,950 --> 01:08:01,200
And how is that shown?

1246
01:08:01,200 --> 01:08:03,590
Well, octopus cells
are just there,

1247
01:08:03,590 --> 01:08:05,550
but you can get
some Onset responses

1248
01:08:05,550 --> 01:08:07,570
in various places in
the cochlear nucleus.

1249
01:08:07,570 --> 01:08:10,120
And I'll tell you
how this dashed arrow

1250
01:08:10,120 --> 01:08:11,874
was drawn in a minute.

1251
01:08:13,290 --> 01:08:17,710
So Onset units are not
only octopus cells.

1252
01:08:17,710 --> 01:08:22,240
Octopus cells are only
producing the Onset pattern.

1253
01:08:22,240 --> 01:08:24,626
That's the correct
way to say it.

1254
01:08:26,439 --> 01:08:27,590
Right here.

1255
01:08:27,590 --> 01:08:28,089
OK.

1256
01:08:29,910 --> 01:08:32,880
Now, elsewhere in
the cochlear nucleus,

1257
01:08:32,880 --> 01:08:35,550
the cells tend to be mixed up.

1258
01:08:35,550 --> 01:08:38,970
And you can't make very
good regional distinctions--

1259
01:08:38,970 --> 01:08:41,664
in spite of what's said here--
with one other exception.

1260
01:08:42,700 --> 01:08:45,020
In the dorsal
cochlear nucleus there

1261
01:08:45,020 --> 01:08:48,190
is a layer called the
fusiform cell layer.

1262
01:08:49,490 --> 01:08:53,190
And so it has the
pyramidal fusiform cells.

1263
01:08:54,420 --> 01:09:02,109
And there you get Pausers.

1264
01:09:02,109 --> 01:09:05,439
And that's pretty
much the only place--

1265
01:09:05,439 --> 01:09:07,529
well, not completely
the only place--

1266
01:09:07,529 --> 01:09:10,720
you get some deeper in the DCN.

1267
01:09:10,720 --> 01:09:15,810
But that's very good evidence
that the pyramidal cells

1268
01:09:15,810 --> 01:09:18,580
produce a Pauser
type of response.

1269
01:09:18,580 --> 01:09:20,822
You get no Pauser
responses anywhere

1270
01:09:20,822 --> 01:09:22,155
in the ventral cochlear nucleus.

1271
01:09:24,609 --> 01:09:28,399
Now, why am I messing around
with these messy data when,

1272
01:09:28,399 --> 01:09:31,689
to a certain extent, most of
the cochlear nucleus cells

1273
01:09:31,689 --> 01:09:33,040
are all mixed up together?

1274
01:09:33,040 --> 01:09:35,850
Well, you can
build up these data

1275
01:09:35,850 --> 01:09:38,100
from thousands of
recordings, and you

1276
01:09:38,100 --> 01:09:40,109
can look at hundreds
of cochlear nuclei.

1277
01:09:40,109 --> 01:09:43,240
You can assure yourself
this is the only place

1278
01:09:43,240 --> 01:09:44,530
that octopus cells are found.

1279
01:09:45,729 --> 01:09:47,689
You can record from
thousands of units

1280
01:09:47,689 --> 01:09:50,681
and not find too many
Onset responses elsewhere

1281
01:09:50,681 --> 01:09:51,680
in the cochlear nucleus.

1282
01:09:51,680 --> 01:09:54,820
So you have the strength
of numbers behind you

1283
01:09:54,820 --> 01:09:56,615
if you use this
type of approach.

1284
01:09:57,920 --> 01:10:01,035
We talked last time about
single unit labeling.

1285
01:10:02,120 --> 01:10:05,890
Why not apply that to the
cochlear nucleus neurons?

1286
01:10:05,890 --> 01:10:06,970
OK.

1287
01:10:06,970 --> 01:10:09,520
The way you do that is
you fill your electrode

1288
01:10:09,520 --> 01:10:10,450
with neural tracer.

1289
01:10:12,180 --> 01:10:13,470
You go in.

1290
01:10:13,470 --> 01:10:17,180
You record the CF
from the tuning curve.

1291
01:10:17,180 --> 01:10:20,340
Then you turn a tone on
and you get the unit type.

1292
01:10:20,340 --> 01:10:22,000
Is it a Primarylike
or is it a Chopper?

1293
01:10:23,590 --> 01:10:26,250
That's a very elegant way
to answer this question,

1294
01:10:26,250 --> 01:10:29,180
and it's been done, but it's
also extremely difficult.

1295
01:10:31,280 --> 01:10:35,280
For some reason, recording
from the cochlear nucleus

1296
01:10:35,280 --> 01:10:38,860
neurons with the type of
pipette [? electrode ?] that's

1297
01:10:38,860 --> 01:10:41,390
necessary to have your
neural tracer in it,

1298
01:10:41,390 --> 01:10:42,990
it's very difficult.

1299
01:10:42,990 --> 01:10:45,780
You get the recording and
then you go inside the cell

1300
01:10:45,780 --> 01:10:49,930
to inject it, and it tears
a big hole in the membrane.

1301
01:10:49,930 --> 01:10:51,620
And so the neuron
stops responding.

1302
01:10:51,620 --> 01:10:52,787
Have you lost the neuron?

1303
01:10:52,787 --> 01:10:53,620
Are you still in it?

1304
01:10:53,620 --> 01:10:54,250
You don't know.

1305
01:10:56,700 --> 01:10:58,850
OK, so that's very
difficult to do,

1306
01:10:58,850 --> 01:11:02,350
but it has been done on
this certain select number

1307
01:11:02,350 --> 01:11:02,870
of neurons.

1308
01:11:02,870 --> 01:11:05,430
And here's some data from
single unit labeling.

1309
01:11:07,230 --> 01:11:11,440
So here is from a study--
this is from a study

1310
01:11:11,440 --> 01:11:15,830
by Bill Rhode et al at the
University of Wisconsin,

1311
01:11:15,830 --> 01:11:18,070
in which he recorded
from cochlear

1312
01:11:18,070 --> 01:11:21,220
nucleus, Primarylike neurons.

1313
01:11:21,220 --> 01:11:24,870
That's clearly a
Primarylike PST.

1314
01:11:24,870 --> 01:11:27,060
He injected and
labeled the neuron

1315
01:11:27,060 --> 01:11:30,580
and recovered in the
ventral cochlear nucleus.

1316
01:11:30,580 --> 01:11:33,590
And there's what the
labeled neuron looks like.

1317
01:11:33,590 --> 01:11:37,460
There's a big cell with
one primary dendrite,

1318
01:11:37,460 --> 01:11:40,520
with lots of ramifications
close by the cell.

1319
01:11:40,520 --> 01:11:43,870
It's not as clear as the bushy
cell I drew on the board,

1320
01:11:43,870 --> 01:11:46,110
but clearly this
is a bushy cell,

1321
01:11:46,110 --> 01:11:50,080
because all the
dendrites are close by.

1322
01:11:50,080 --> 01:11:56,680
Now, I'm using the nomenclature
from the Golgi stain

1323
01:11:56,680 --> 01:12:01,610
because, clearly, that cell
is stained in its entirety.

1324
01:12:01,610 --> 01:12:03,480
The cell body is black.

1325
01:12:03,480 --> 01:12:08,220
The dendrites, every little
type of dendrite ramification

1326
01:12:08,220 --> 01:12:09,780
is filled black.

1327
01:12:09,780 --> 01:12:13,930
That big thread-like thing
going right underneath the title

1328
01:12:13,930 --> 01:12:15,850
labeled neuron is the axon.

1329
01:12:15,850 --> 01:12:18,830
You can trace the axon
wherever you want to.

1330
01:12:18,830 --> 01:12:21,390
This is Golgi-like
labeling that you

1331
01:12:21,390 --> 01:12:25,060
get from filling these
cells with neural tracer.

1332
01:12:25,060 --> 01:12:27,320
Clearly, that's a bushy cell.

1333
01:12:27,320 --> 01:12:28,860
And it had a
Primarylike pattern.

1334
01:12:28,860 --> 01:12:31,350
Now, if you look in
all the literature,

1335
01:12:31,350 --> 01:12:36,570
maybe you get about eight
or 10 filled bushy cells.

1336
01:12:36,570 --> 01:12:40,420
And people have spent many
years trying to do this.

1337
01:12:40,420 --> 01:12:43,240
You see papers published
with just a half a dozen

1338
01:12:43,240 --> 01:12:44,210
labeled neurons.

1339
01:12:44,210 --> 01:12:45,560
It's very difficult to do.

1340
01:12:46,660 --> 01:12:49,120
But clearly, that
Primarylike pattern

1341
01:12:49,120 --> 01:12:51,010
came from that bushy cell.

1342
01:12:51,010 --> 01:12:54,910
This Chopper pattern-- this
is a subtype of Chopper--

1343
01:12:54,910 --> 01:12:56,900
came from the stellate cell.

1344
01:12:56,900 --> 01:12:59,780
Clearly, rather than
one primary dendrite,

1345
01:12:59,780 --> 01:13:01,300
it had a half a dozen.

1346
01:13:01,300 --> 01:13:02,920
And the dendrites went forever.

1347
01:13:02,920 --> 01:13:05,020
Here's a neuron that
sent its dendrites

1348
01:13:05,020 --> 01:13:07,370
all across the cochlear nucleus.

1349
01:13:07,370 --> 01:13:10,101
Clearly a different type
of cell-- a stellate cell.

1350
01:13:12,790 --> 01:13:15,810
OK, so let's draw an arrow
there for those two neurons.

1351
01:13:20,690 --> 01:13:21,485
Bushy cells.

1352
01:13:24,320 --> 01:13:25,650
Spherical bushy cells.

1353
01:13:25,650 --> 01:13:33,007
We actually don't know
that it's spherical-- can

1354
01:13:33,007 --> 01:13:33,840
produce Primarylike.

1355
01:13:35,120 --> 01:13:39,975
Stellates can produce
Chopping patterns.

1356
01:13:43,350 --> 01:13:46,270
And these other
correlations-- octopus

1357
01:13:46,270 --> 01:13:50,140
cells correlated with Onset,
we already established.

1358
01:13:50,140 --> 01:13:54,680
And Pauser types correlated
with pyramidal fusiform cells,

1359
01:13:54,680 --> 01:13:56,510
we already established.

1360
01:13:56,510 --> 01:14:02,050
So we here have a nice
chart of correlations

1361
01:14:02,050 --> 01:14:04,280
between the anatomy
and the physiology.

1362
01:14:04,280 --> 01:14:07,040
And probably, this can be done
much better in cochlear nucleus

1363
01:14:07,040 --> 01:14:08,857
than any other
center in the brain.

1364
01:14:08,857 --> 01:14:10,190
Auditory system or non-auditory.

1365
01:14:11,780 --> 01:14:12,280
OK?

1366
01:14:13,390 --> 01:14:17,250
Now, you should be a
little bit skeptical of me,

1367
01:14:17,250 --> 01:14:21,410
as scientists, when I
give you these really

1368
01:14:21,410 --> 01:14:23,295
nice classification schemes.

1369
01:14:24,580 --> 01:14:35,070
So what is really the difference
between a globular bushy

1370
01:14:35,070 --> 01:14:38,150
cell and a spherical bushy cell?

1371
01:14:38,150 --> 01:14:41,580
You should be thinking,
"Can that guy really

1372
01:14:41,580 --> 01:14:42,710
make that distinction?"

1373
01:14:42,710 --> 01:14:45,480
OK, sure, some
things are spheres,

1374
01:14:45,480 --> 01:14:47,030
and some things are oblong.

1375
01:14:47,030 --> 01:14:48,685
But what about
something in between?

1376
01:14:50,160 --> 01:14:53,890
Are there intermediates in
this classification scheme?

1377
01:14:53,890 --> 01:14:57,490
So let me give you just an
arbitrary-- we classify people

1378
01:14:57,490 --> 01:14:58,996
by the color of
their hair, right?

1379
01:14:58,996 --> 01:14:59,746
There are blondes.

1380
01:15:00,930 --> 01:15:02,700
There black-haired people.

1381
01:15:02,700 --> 01:15:04,720
There are brown-haired people.

1382
01:15:04,720 --> 01:15:05,540
There are red-head.

1383
01:15:05,540 --> 01:15:07,540
But then you have a lot
of intermediates, right?

1384
01:15:07,540 --> 01:15:09,250
You have dirty blondes.

1385
01:15:09,250 --> 01:15:13,930
You have people who
have darkish brown hair,

1386
01:15:13,930 --> 01:15:15,995
not quite black,
but not quite brown.

1387
01:15:16,690 --> 01:15:18,940
What are you going to do
with all those intermediates?

1388
01:15:18,940 --> 01:15:20,440
What are you going
to do with people

1389
01:15:20,440 --> 01:15:21,560
who are losing their hair?

1390
01:15:21,560 --> 01:15:24,866
Problems with
classification schemes

1391
01:15:24,866 --> 01:15:26,490
are if you have a
lot of intermediates.

1392
01:15:28,080 --> 01:15:30,110
And then these
things break down.

1393
01:15:30,110 --> 01:15:32,340
Instead of being a
nice, firm category

1394
01:15:32,340 --> 01:15:34,980
they become really
squishy, with a lot

1395
01:15:34,980 --> 01:15:37,030
of intermediates
between the two.

1396
01:15:38,490 --> 01:15:42,390
It turns out, here, that
that's not a huge problem,

1397
01:15:42,390 --> 01:15:44,335
although it is
sometimes a problem.

1398
01:15:45,680 --> 01:15:47,970
The aficionados who
do this for a living

1399
01:15:47,970 --> 01:15:51,420
have metrics where
you can measure

1400
01:15:51,420 --> 01:15:56,670
the sphericity of a cell or
the oblateness of a cell.

1401
01:15:58,460 --> 01:16:02,040
You can measure things in
the physiological response.

1402
01:16:02,040 --> 01:16:07,830
Like if it's a pause longer
than two milliseconds,

1403
01:16:07,830 --> 01:16:09,870
it's a Pauser unit.

1404
01:16:09,870 --> 01:16:12,230
But if the pause is less
than two milliseconds,

1405
01:16:12,230 --> 01:16:15,080
then it's a notch,
or something else.

1406
01:16:16,980 --> 01:16:17,710
OK.

1407
01:16:17,710 --> 01:16:22,340
So it turns out that there
aren't very many intermediates

1408
01:16:22,340 --> 01:16:25,770
or things that are hard
to classify in these two

1409
01:16:25,770 --> 01:16:29,160
kinds of classification scheme,
which is very important.

1410
01:16:30,860 --> 01:16:35,850
Another important thing is what
do these classifications then

1411
01:16:35,850 --> 01:16:36,350
predict?

1412
01:16:37,620 --> 01:16:41,880
If you're recording
from a Primarylike unit,

1413
01:16:41,880 --> 01:16:45,190
and you say it's one of
these kinds of bushy cells,

1414
01:16:45,190 --> 01:16:46,190
what does it predict?

1415
01:16:46,190 --> 01:16:51,690
Well, one thing it predicts
is where the cells project to.

1416
01:16:51,690 --> 01:16:54,470
Now, that's given to you a
little bit on this diagram

1417
01:16:54,470 --> 01:16:56,840
here, by this category.

1418
01:16:56,840 --> 01:17:01,290
That says acoustic stria
for the efferent axon.

1419
01:17:01,290 --> 01:17:03,180
And so now we're
using terminology

1420
01:17:03,180 --> 01:17:05,190
that is centric to
the cochlear nucleus.

1421
01:17:05,190 --> 01:17:07,255
Efferent means going out
of the cochlear nucleus.

1422
01:17:08,380 --> 01:17:10,470
And there are three
major pathways

1423
01:17:10,470 --> 01:17:12,000
going out of the
cochlear nucleus.

1424
01:17:12,000 --> 01:17:14,285
The ventral,
intermediate, and dorsal.

1425
01:17:16,010 --> 01:17:19,060
And different types
of cells project

1426
01:17:19,060 --> 01:17:23,650
in one or another, but not all
three of these output pathways.

1427
01:17:23,650 --> 01:17:27,860
So knowing the type of cell,
knowing its response pattern,

1428
01:17:27,860 --> 01:17:32,060
I can predict where
the axon is going.

1429
01:17:32,060 --> 01:17:35,260
So the predictability of
the classification scheme,

1430
01:17:35,260 --> 01:17:38,160
if it predicts things
very well, means

1431
01:17:38,160 --> 01:17:39,930
that it's a good
classification scheme.

1432
01:17:39,930 --> 01:17:42,600
But when somebody gives you
a classification scheme,

1433
01:17:42,600 --> 01:17:44,100
you should always
be thinking, "Now,

1434
01:17:44,100 --> 01:17:46,580
is it a good
classification scheme?

1435
01:17:46,580 --> 01:17:48,742
Or it is just
something cooked up?"

1436
01:17:48,742 --> 01:17:50,450
Meaning, are there
lots of intermediates?

1437
01:17:53,490 --> 01:17:55,925
So speaking of
projections of the axons.

1438
01:17:57,820 --> 01:18:01,325
This is what I want
to end up with today.

1439
01:18:03,690 --> 01:18:05,490
Especially in terms
of the parallel

1440
01:18:05,490 --> 01:18:08,730
pathways that we talked
about at the beginning

1441
01:18:08,730 --> 01:18:09,655
of today's lecture.

1442
01:18:11,080 --> 01:18:13,460
So here's another
even different type

1443
01:18:13,460 --> 01:18:15,570
of diagram of the
cochlear nucleus.

1444
01:18:15,570 --> 01:18:18,460
This is the cochlear
nucleus on the left side.

1445
01:18:19,690 --> 01:18:21,190
This is a little
bit of the cochlear

1446
01:18:21,190 --> 01:18:23,340
nucleus on the right side.

1447
01:18:23,340 --> 01:18:27,360
And so we have a whole bunch
of the auditory pathway,

1448
01:18:27,360 --> 01:18:32,500
the superior olivary complex,
and the inferior colliculus

1449
01:18:32,500 --> 01:18:34,520
more in the center of the brain.

1450
01:18:34,520 --> 01:18:37,230
And now you can
get a sense of why

1451
01:18:37,230 --> 01:18:39,155
the superior olive
is really a complex.

1452
01:18:40,330 --> 01:18:41,460
Here are parts of it.

1453
01:18:41,460 --> 01:18:43,025
Lateral superior olive.

1454
01:18:44,140 --> 01:18:45,505
Medial superior olive.

1455
01:18:46,560 --> 01:18:50,010
Medial nucleus of
the trapezoid body.

1456
01:18:50,010 --> 01:18:52,350
Lateral nucleus of
the trapezoid body.

1457
01:18:52,350 --> 01:18:55,570
And that's just part of the
superior olivary complex.

1458
01:18:55,570 --> 01:18:58,220
It's really a whole
bunch of different nuclei

1459
01:18:58,220 --> 01:18:59,355
all glommed together.

1460
01:19:01,240 --> 01:19:04,430
The point of this slide,
though, is the projections

1461
01:19:04,430 --> 01:19:07,030
of the cochlear nucleus
neurons, in terms

1462
01:19:07,030 --> 01:19:09,840
of where they send axons to.

1463
01:19:09,840 --> 01:19:16,190
So here are the spherical
bushy cells, right here.

1464
01:19:17,500 --> 01:19:18,790
That's its diagram here.

1465
01:19:18,790 --> 01:19:21,170
And this little
lending is supposed

1466
01:19:21,170 --> 01:19:24,410
to be the giant end bulb
of Held that they receive.

1467
01:19:24,410 --> 01:19:27,880
The spherical bushy cell on
the left cochlear nucleus

1468
01:19:27,880 --> 01:19:33,730
projects up here into the
left superior olivary complex.

1469
01:19:33,730 --> 01:19:36,280
And one of its most
important places to end up

1470
01:19:36,280 --> 01:19:38,330
is in the medial superior olive.

1471
01:19:39,640 --> 01:19:41,320
Part of the superior
olivary complex.

1472
01:19:43,230 --> 01:19:47,690
And it continues on and
goes across the midline

1473
01:19:47,690 --> 01:19:50,960
and also projects into the
right medial superior olive.

1474
01:19:53,580 --> 01:19:58,930
It's not diagrammed here, but
analogous spherical bushy cells

1475
01:19:58,930 --> 01:20:01,760
on the right side come
in and do the same thing.

1476
01:20:03,820 --> 01:20:06,830
The medial superior
olive is the place--

1477
01:20:06,830 --> 01:20:11,310
that we'll study in about a
week-- that receives input

1478
01:20:11,310 --> 01:20:14,345
from the two sides from
the spherical bushy cells.

1479
01:20:15,800 --> 01:20:20,580
And it compares the timing of
the inputs from the two sides.

1480
01:20:20,580 --> 01:20:23,440
It says, oh, if I heard
the sound on the left side

1481
01:20:23,440 --> 01:20:27,380
a little bit earlier,
then that sound source

1482
01:20:27,380 --> 01:20:29,530
was located to the
left side of my body.

1483
01:20:30,790 --> 01:20:36,410
But if the MSO gets input
from the right side first,

1484
01:20:36,410 --> 01:20:38,850
it's almost certainly the
case that the sound source

1485
01:20:38,850 --> 01:20:41,490
was located on the
right side of the body.

1486
01:20:41,490 --> 01:20:44,390
And it'd activate the right
ear and the right cochlear

1487
01:20:44,390 --> 01:20:46,700
nucleus and its axons first.

1488
01:20:46,700 --> 01:20:50,860
And by the time the sound leaked
around to the left ear-- it

1489
01:20:50,860 --> 01:20:53,670
a longer time to travel,
here-- and started

1490
01:20:53,670 --> 01:20:57,320
to activate the left pathway,
it was a lagging signal

1491
01:20:57,320 --> 01:20:59,520
and came into the MSO
a little bit later.

1492
01:21:00,770 --> 01:21:03,860
So the MSO, then,
receiving input

1493
01:21:03,860 --> 01:21:09,260
from these two spherical bushy
cells from the two cochlear

1494
01:21:09,260 --> 01:21:12,660
nuclei, does an
interesting comparison

1495
01:21:12,660 --> 01:21:16,775
and helps us localize the
sound using timing differences.

1496
01:21:18,750 --> 01:21:21,440
There's probably
a pathway in here

1497
01:21:21,440 --> 01:21:24,070
that begins with the
globular bushy cells,

1498
01:21:24,070 --> 01:21:28,160
where you use the differences
in level at the two ears

1499
01:21:28,160 --> 01:21:29,195
to localize sounds.

1500
01:21:30,240 --> 01:21:34,390
That's two out of maybe 10
different types of cells

1501
01:21:34,390 --> 01:21:36,610
that we really
know what they do.

1502
01:21:36,610 --> 01:21:40,860
So the other eight or
so-- the pyramidal cells,

1503
01:21:40,860 --> 01:21:44,780
the small cells, the octopus
cells, the stellate cells--

1504
01:21:44,780 --> 01:21:47,230
we have no idea what they do.

1505
01:21:47,230 --> 01:21:47,730
OK?

1506
01:21:47,730 --> 01:21:50,970
So all the rest of these
other parallel pathways,

1507
01:21:50,970 --> 01:21:52,430
the function are unknown.

1508
01:21:52,430 --> 01:21:55,600
We think they do something
in the sense of hearing,

1509
01:21:55,600 --> 01:21:57,200
but we're not sure what they do.

1510
01:21:57,200 --> 01:22:00,910
So there's a lot of
interesting information left

1511
01:22:00,910 --> 01:22:04,160
to be gleaned from these
parallel pathways coming out

1512
01:22:04,160 --> 01:22:05,160
of the cochlear nucleus.

1513
01:22:06,521 --> 01:22:07,020
OK?

1514
01:22:07,020 --> 01:22:10,540
So that's what I
want to end up with.

1515
01:22:10,540 --> 01:22:12,950
If there are any questions,
I'll take them now.

1516
01:22:14,210 --> 01:22:17,460
I also want to remind you
guys that next week, Monday

1517
01:22:17,460 --> 01:22:19,465
is a holiday, so there
won't be any class.

1518
01:22:20,520 --> 01:22:23,930
So the next time we meet is a
week from today, on Wednesday.

1519
01:22:25,100 --> 01:22:27,150
And in that lecture,
we're going to talk

1520
01:22:27,150 --> 01:22:29,770
about deafness and hearing
loss, and toward the end we'll

1521
01:22:29,770 --> 01:22:33,130
have our demonstrator come in
to demonstrate her cochlear

1522
01:22:33,130 --> 01:22:33,650
implants.

1523
01:22:33,650 --> 01:22:35,670
So that's an important
class, not to be missed.

1524
01:22:37,050 --> 01:22:39,120
OK, have a good mini-vacation.