1 00:00:00,250 --> 00:00:01,800 The following content is provided 2 00:00:01,800 --> 00:00:04,040 under a Creative Commons license. 3 00:00:04,040 --> 00:00:06,890 Your support will help MIT OpenCourseWare continue 4 00:00:06,890 --> 00:00:10,750 to offer high quality educational resources for free. 5 00:00:10,750 --> 00:00:13,360 To make a donation or view additional materials 6 00:00:13,360 --> 00:00:17,239 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:17,239 --> 00:00:17,864 at ocw.mit.edu. 8 00:00:22,882 --> 00:00:24,340 PROFESSOR: I'll let you know, we'll 9 00:00:24,340 --> 00:00:28,390 probably have two quizzes next week. 10 00:00:28,390 --> 00:00:32,930 I want to give you a very simple quiz that I 11 00:00:32,930 --> 00:00:37,630 used to give every year in 914, in which you simply 12 00:00:37,630 --> 00:00:45,970 list the cranial nerves, their names, the number, the name, 13 00:00:45,970 --> 00:00:48,700 whether they're sensory, motor, or both. 14 00:00:51,990 --> 00:00:55,480 There's a table, I believe, in the book. 15 00:00:55,480 --> 00:01:00,270 So let me look at that and we'll send an email around 16 00:01:00,270 --> 00:01:01,380 about that. 17 00:01:01,380 --> 00:01:02,820 I think it's very useful to know. 18 00:01:02,820 --> 00:01:05,610 It's just one of those outlines that you 19 00:01:05,610 --> 00:01:08,480 need to have in your mind. 20 00:01:08,480 --> 00:01:10,150 So when you encounter it-- 21 00:01:10,150 --> 00:01:10,630 AUDIENCE: I think I memorized it. 22 00:01:10,630 --> 00:01:12,005 I don't know if you asked or not. 23 00:01:13,614 --> 00:01:14,280 PROFESSOR: Yeah. 24 00:01:14,280 --> 00:01:17,250 I learned a little mnemonic. 25 00:01:17,250 --> 00:01:20,530 I think I give it in the book. 26 00:01:20,530 --> 00:01:23,440 I just memorized the mnemonic, and then I had no trouble. 27 00:01:23,440 --> 00:01:26,664 Because you hear those names enough that 28 00:01:26,664 --> 00:01:30,390 it's easy enough to learn it. 29 00:01:30,390 --> 00:01:32,518 All right, so auditory system. 30 00:01:37,090 --> 00:01:44,510 We had ended by talking a little bit about coding, frequency, 31 00:01:44,510 --> 00:01:49,390 and intensity and the auditory nerve. 32 00:01:49,390 --> 00:01:54,550 And then how it's the spatial map of the basilar membrane 33 00:01:54,550 --> 00:01:58,500 is preserved in the organization of the axons coming 34 00:01:58,500 --> 00:02:04,240 into the cochlear nuclei here. 35 00:02:04,240 --> 00:02:11,480 And I want to just review the sensory channels, what 36 00:02:11,480 --> 00:02:13,430 happens to that information that comes 37 00:02:13,430 --> 00:02:16,607 in through the eighth nerve, the auditory component 38 00:02:16,607 --> 00:02:17,440 of the eighth nerve. 39 00:02:17,440 --> 00:02:21,260 We're not going to talk much about vestibular. 40 00:02:21,260 --> 00:02:25,280 But if you learn the auditory system, 41 00:02:25,280 --> 00:02:31,130 vestibular is not that different. 42 00:02:31,130 --> 00:02:34,620 It's less studied, but the hindbrain mechanisms 43 00:02:34,620 --> 00:02:36,325 are studied the most because they 44 00:02:36,325 --> 00:02:42,956 are important in some human problems. 45 00:02:42,956 --> 00:02:45,840 And of course, to the neurologist dizziness 46 00:02:45,840 --> 00:02:47,830 is a common complaint that people have, 47 00:02:47,830 --> 00:02:51,086 and he has to understand something about that system. 48 00:02:51,086 --> 00:02:54,410 But then we want to get to studying the two 49 00:02:54,410 --> 00:02:57,170 major ascending pathways. 50 00:02:57,170 --> 00:02:58,880 In the auditory system you can divide 51 00:02:58,880 --> 00:03:01,010 ascending pathways pretty early on. 52 00:03:01,010 --> 00:03:04,540 And the pathways more concerned with identifying 53 00:03:04,540 --> 00:03:08,600 patterns, generally temporal patterns of the stimulus, 54 00:03:08,600 --> 00:03:11,340 and they keep frequency separated all the way up 55 00:03:11,340 --> 00:03:14,900 to the auditory cortex. 56 00:03:14,900 --> 00:03:18,980 And then pathways concerned with localization in space, 57 00:03:18,980 --> 00:03:22,010 [INAUDIBLE] for that. 58 00:03:22,010 --> 00:03:24,610 So this is the system that you gradually 59 00:03:24,610 --> 00:03:28,730 come to understand more and more as we go through this. 60 00:03:28,730 --> 00:03:30,750 These are the basic channels. 61 00:03:30,750 --> 00:03:35,335 We talk about a reflex channel, just short pathways 62 00:03:35,335 --> 00:03:38,130 that begin in the cochlear nuclei. 63 00:03:38,130 --> 00:03:43,040 Mostly ventral cochlear nucleus, but both of the cochlear 64 00:03:43,040 --> 00:03:46,480 nuclei that just project to brainstem neurons 65 00:03:46,480 --> 00:03:48,950 that have pretty short reflex connections. 66 00:03:48,950 --> 00:03:54,060 And startle is just one of them. 67 00:03:54,060 --> 00:03:56,240 And then the cerebellar pathways, 68 00:03:56,240 --> 00:04:00,960 which could be considered a type of lemniscal channel. 69 00:04:00,960 --> 00:04:03,750 You see it here. 70 00:04:03,750 --> 00:04:07,620 I show a pathway from the dorsal cochlear nucleus, 71 00:04:07,620 --> 00:04:10,072 as well as through a reflex. 72 00:04:14,500 --> 00:04:16,190 And then the lemniscal channels. 73 00:04:16,190 --> 00:04:20,089 There are two major routes to the inferior colliculus, 74 00:04:20,089 --> 00:04:21,489 two separate routes. 75 00:04:21,489 --> 00:04:24,300 And the inferior colliculus projects heavily 76 00:04:24,300 --> 00:04:28,140 to the thalamus and the medial geniculate body. 77 00:04:28,140 --> 00:04:33,120 Medial because it's-- in the human, it's another bump, 78 00:04:33,120 --> 00:04:38,360 a geniculate structure that's medial to the lateral one. 79 00:04:38,360 --> 00:04:43,700 The visual input comes in from the retina. 80 00:04:43,700 --> 00:04:46,080 There is a smaller route that's more 81 00:04:46,080 --> 00:04:52,321 prominent in the large mammals. 82 00:04:52,321 --> 00:04:54,340 It was actually discovered first in the chimp. 83 00:04:54,340 --> 00:04:56,760 But then they looked with more sensitive methods 84 00:04:56,760 --> 00:04:59,502 and they realized it's even there in the rat. 85 00:04:59,502 --> 00:05:02,484 A pathway directly from the dorsal cochlear 86 00:05:02,484 --> 00:05:05,040 nucleus to the medial geniculate body. 87 00:05:05,040 --> 00:05:08,670 But then there's a route that we think may be older, 88 00:05:08,670 --> 00:05:11,580 that is here in gray. 89 00:05:11,580 --> 00:05:16,670 I show it coming from the trapezoid body primarily. 90 00:05:16,670 --> 00:05:20,610 Which gets its input, many neurons in the trapezoid body 91 00:05:20,610 --> 00:05:24,190 region here, which contains a lot of crossing fibers 92 00:05:24,190 --> 00:05:27,170 related to the auditory system. 93 00:05:27,170 --> 00:05:30,190 That travels through the reticular formation 94 00:05:30,190 --> 00:05:34,030 also to these nuclei at the lateral lemniscus. 95 00:05:34,030 --> 00:05:36,910 The axons continue forward through the midbrain, 96 00:05:36,910 --> 00:05:39,330 some of them go into the superior colliculus. 97 00:05:39,330 --> 00:05:41,510 They don't terminate in the main nucleus 98 00:05:41,510 --> 00:05:42,810 of the medial geniculus. 99 00:05:42,810 --> 00:05:45,320 They terminate in cells around it, 100 00:05:45,320 --> 00:05:47,240 including many cells that are multi-modal. 101 00:05:50,230 --> 00:05:52,040 There are uni-modal regions, too. 102 00:05:52,040 --> 00:05:56,980 This It's just called part of the posterior group of nuclei. 103 00:05:56,980 --> 00:06:01,580 But it includes a nucleus that's called the medial nucleus 104 00:06:01,580 --> 00:06:03,460 of the medial geniculate body. 105 00:06:17,390 --> 00:06:21,780 I just want to say a little more about the eighth nerve. 106 00:06:21,780 --> 00:06:26,310 You know that axons representing different frequencies 107 00:06:26,310 --> 00:06:29,670 terminate in this organized way in the two nuclei. 108 00:06:29,670 --> 00:06:31,890 The nerve comes in from below. 109 00:06:31,890 --> 00:06:37,820 And then a similar thing happens in the ventral cochlear nuclei, 110 00:06:37,820 --> 00:06:39,470 anterior and posterior divisions, 111 00:06:39,470 --> 00:06:42,170 and in the dorsal cochlear nucleus. 112 00:06:42,170 --> 00:06:45,200 Where axons from different parts of the basilar 113 00:06:45,200 --> 00:06:47,840 membrane, different parts of the cochlea, 114 00:06:47,840 --> 00:06:49,740 terminate at different levels. 115 00:06:49,740 --> 00:06:53,580 So if you penetrate this way, you'd 116 00:06:53,580 --> 00:06:56,610 see the representational frequency. 117 00:06:56,610 --> 00:07:00,415 Now if you look at one of these axons, 118 00:07:00,415 --> 00:07:07,733 it travels rostrocaudally through the nucleus. 119 00:07:14,640 --> 00:07:17,505 This would be like those rostrocaudal axons 120 00:07:17,505 --> 00:07:21,160 that I just showed you along here. 121 00:07:21,160 --> 00:07:23,290 What they're showing in this picture, 122 00:07:23,290 --> 00:07:26,912 this is originally from Nelson Kiang here at MIT. 123 00:07:26,912 --> 00:07:28,790 He still comes to talks here. 124 00:07:28,790 --> 00:07:31,380 I met him just the other day. 125 00:07:31,380 --> 00:07:33,770 He did a lot of this work on the eighth nerve. 126 00:07:33,770 --> 00:07:35,322 And what he's showing in this picture 127 00:07:35,322 --> 00:07:39,380 is different cell types in the ventral cochlear nucleus. 128 00:07:39,380 --> 00:07:45,224 And he investigated how these respond 129 00:07:45,224 --> 00:07:53,915 to a pulse of sound, graphed here. 130 00:07:56,730 --> 00:07:59,260 This is the tone burst. 131 00:07:59,260 --> 00:08:03,620 And here's how the eighth nerve axon responds. 132 00:08:03,620 --> 00:08:06,170 A lot of the action potential is right at the beginning. 133 00:08:06,170 --> 00:08:09,950 And then it sort of levels off at a lower level. 134 00:08:09,950 --> 00:08:11,690 And you'll note here, if you look 135 00:08:11,690 --> 00:08:16,350 at the responses of these cells, there's 136 00:08:16,350 --> 00:08:22,230 one type that pretty much matches this. 137 00:08:22,230 --> 00:08:30,175 They call it a primary-like post-synaptic train 138 00:08:30,175 --> 00:08:32,409 of action potentials. 139 00:08:32,409 --> 00:08:36,590 So my question is, how can that happen? 140 00:08:36,590 --> 00:08:39,400 Because normally, no matter where 141 00:08:39,400 --> 00:08:41,110 you are in the central nervous system, 142 00:08:41,110 --> 00:08:44,070 cells don't fire when there's only one action potential. 143 00:08:44,070 --> 00:08:46,690 There's got to be a lot of summation. 144 00:08:46,690 --> 00:08:48,600 Either it's ready to fire because there's 145 00:08:48,600 --> 00:08:50,900 a lot of other excitatory input coming in. 146 00:08:56,340 --> 00:08:58,220 There's also some spontaneous activity. 147 00:08:58,220 --> 00:09:01,050 And if it's near the point where it's going to fire anyway 148 00:09:01,050 --> 00:09:04,410 and it might fire a little earlier if there's input. 149 00:09:04,410 --> 00:09:07,420 But how does this happen reliably? 150 00:09:07,420 --> 00:09:11,810 And why is reliability so important for those nerves? 151 00:09:11,810 --> 00:09:17,010 It's important because it's used as a cue to position in space. 152 00:09:17,010 --> 00:09:21,620 Because the input from the two ears is compared. 153 00:09:21,620 --> 00:09:23,840 And I talk about the chick system, 154 00:09:23,840 --> 00:09:26,110 because it's a little simpler than the mammal 155 00:09:26,110 --> 00:09:28,950 and it's been easier to study. 156 00:09:28,950 --> 00:09:31,830 The studies are better for the chick 157 00:09:31,830 --> 00:09:33,920 than they are for the mammal. 158 00:09:33,920 --> 00:09:36,940 You've got to know what the endbulb of Held is. 159 00:09:36,940 --> 00:09:44,120 These are endings of eight nerve axons on some of these cells. 160 00:09:44,120 --> 00:09:49,350 Cells like this, they're spherical bushy cells. 161 00:09:49,350 --> 00:09:53,030 In the chick they're just balled cells. 162 00:09:53,030 --> 00:09:56,220 During development they have a lot of dendrites. 163 00:09:56,220 --> 00:09:59,320 They pull them all in with development. 164 00:09:59,320 --> 00:10:07,670 And this terminal distributes over the cell like a cup. 165 00:10:07,670 --> 00:10:11,330 There's a similar ending in trapezoid body 166 00:10:11,330 --> 00:10:13,060 that's called the Calyx of Held. 167 00:10:13,060 --> 00:10:16,980 They were both described by this anatomist Held. 168 00:10:16,980 --> 00:10:20,700 I used to call it the Calyx of Held and the cochlear nucleus. 169 00:10:20,700 --> 00:10:24,600 But then I read the history and realized that he actually 170 00:10:24,600 --> 00:10:27,170 described the one in the trapezoid body. 171 00:10:27,170 --> 00:10:30,530 He also described this one, but didn't call it calyx. 172 00:10:33,065 --> 00:10:35,840 So people call it the endbulb of Held. 173 00:10:35,840 --> 00:10:37,840 But you can see what's happening here. 174 00:10:37,840 --> 00:10:40,250 It forms multiple synapses. 175 00:10:40,250 --> 00:10:45,150 So many different synapses in one bump, one terminal 176 00:10:45,150 --> 00:10:46,180 enlargement. 177 00:10:46,180 --> 00:10:50,096 That means with the action potential one pulse here 178 00:10:50,096 --> 00:10:50,595 arrives. 179 00:10:53,130 --> 00:10:56,260 It causes simultaneous depolarization 180 00:10:56,260 --> 00:10:58,940 at many different points in that membrane. 181 00:10:58,940 --> 00:11:01,970 So they all summate here at the axon hillock, 182 00:11:01,970 --> 00:11:04,875 and you end up with one action potential coming out. 183 00:11:07,590 --> 00:11:09,235 That's pretty unusual in the sense 184 00:11:09,235 --> 00:11:10,318 of central nervous system. 185 00:11:15,910 --> 00:11:19,465 These are just another summary of these connections 186 00:11:19,465 --> 00:11:20,555 through the thalamus. 187 00:11:23,630 --> 00:11:26,420 And these are the summary of the thalamic projects then. 188 00:11:30,000 --> 00:11:32,340 Of course, the medial geniculate body 189 00:11:32,340 --> 00:11:35,140 projects to the auditory cortex in the temporal lobe. 190 00:11:38,200 --> 00:11:42,290 You also get projections to nearby areas 191 00:11:42,290 --> 00:11:47,440 from those posterior nuclei that are getting auditory input. 192 00:11:47,440 --> 00:11:54,230 That's why when I diagram this this way, 193 00:11:54,230 --> 00:11:58,320 I show that these neurons outside of principle nucleus, 194 00:11:58,320 --> 00:12:02,880 in the medial geniculate body, I show them going to area 41. 195 00:12:02,880 --> 00:12:06,760 Whereas these other cells go primarily to the other areas, 196 00:12:06,760 --> 00:12:10,470 especially the areas ventral to the auditory cortex. 197 00:12:10,470 --> 00:12:12,376 These also get transferred connections 198 00:12:12,376 --> 00:12:14,560 from the auditory cortex. 199 00:12:19,860 --> 00:12:28,350 Just remember that cells here and the medial geniculate body 200 00:12:28,350 --> 00:12:32,730 send axons that go not only to neocortex, but also 201 00:12:32,730 --> 00:12:36,200 into the amygdala, the lateral nucleus and amygdala. 202 00:12:36,200 --> 00:12:38,740 And I mentioned there are some visual projections like that 203 00:12:38,740 --> 00:12:42,180 too, to that lateral nucleus, the amygdala. 204 00:12:42,180 --> 00:12:46,970 And that's proved to be pretty important in learned fear 205 00:12:46,970 --> 00:12:48,380 in studies primarily of the rat. 206 00:12:58,620 --> 00:13:07,640 This is what we've just looked at. 207 00:13:07,640 --> 00:13:10,640 And I think I just answered this question, 208 00:13:10,640 --> 00:13:13,160 why do some of the auditory nerve axons that terminate 209 00:13:13,160 --> 00:13:16,820 in the ventricle of the nucleus end in a giant terminal 210 00:13:16,820 --> 00:13:19,260 enlargement? 211 00:13:19,260 --> 00:13:25,100 To answer that you have to describe that endbulb of Held. 212 00:13:25,100 --> 00:13:27,780 What function does it serve? 213 00:13:27,780 --> 00:13:32,780 Can we get enough spatial summation so so one action 214 00:13:32,780 --> 00:13:36,370 potential results in one output action potential? 215 00:13:36,370 --> 00:13:39,140 And you need to know what the trapezoid body is. 216 00:13:42,330 --> 00:13:49,570 In pictures like this, I just show it as down here. 217 00:13:49,570 --> 00:13:53,330 But if you looked at a cross section-- 218 00:13:53,330 --> 00:13:56,770 I really should have a mammalian cross section here, 219 00:13:56,770 --> 00:13:58,710 but they're easy to find. 220 00:13:58,710 --> 00:14:02,360 You find that the cells here, especially 221 00:14:02,360 --> 00:14:07,280 in the ventral cochlear nucleus, project to both sides, 222 00:14:07,280 --> 00:14:10,340 into cell groups in the trapezoid body. 223 00:14:10,340 --> 00:14:12,920 There's a medial nucleus trapezoid body and lateral 224 00:14:12,920 --> 00:14:14,542 nucleus trapezoid body. 225 00:14:18,318 --> 00:14:23,500 And there you have, in mammals, there 226 00:14:23,500 --> 00:14:26,730 is another big Calyx of Held that 227 00:14:26,730 --> 00:14:31,443 preserves that one-on-one response 228 00:14:31,443 --> 00:14:37,970 to auditory input in generating the location information. 229 00:14:37,970 --> 00:14:39,820 Let's look at it in the chick. 230 00:14:44,220 --> 00:14:48,110 Coincidence detectors is a good term for it. 231 00:14:52,910 --> 00:14:55,660 I created this table because some people 232 00:14:55,660 --> 00:14:57,950 have a terrible time if they only see the drawings. 233 00:14:57,950 --> 00:14:59,465 They got to have it all spelled out 234 00:14:59,465 --> 00:15:01,340 in words, so I created the table. 235 00:15:04,964 --> 00:15:10,100 All I'm doing here is putting words to those pictures 236 00:15:10,100 --> 00:15:12,950 that we've already gone over. 237 00:15:12,950 --> 00:15:15,620 So now we'll follow the pathways involved 238 00:15:15,620 --> 00:15:16,610 in these two functions. 239 00:15:16,610 --> 00:15:19,830 We'll begin with the sound localization, which 240 00:15:19,830 --> 00:15:25,770 involves that precise timing we were just talking about. 241 00:15:25,770 --> 00:15:30,960 The pathway that is generating these differences, depending 242 00:15:30,960 --> 00:15:36,260 on where the sound is coming from in the azimuthal plane. 243 00:15:36,260 --> 00:15:38,780 One of the major outputs is to the superior colliculus, 244 00:15:38,780 --> 00:15:43,830 where you have a map of the auditory world. 245 00:15:43,830 --> 00:15:47,860 The spatial map, that is neurons respond best 246 00:15:47,860 --> 00:15:50,880 to sounds coming from a certain position in space. 247 00:15:50,880 --> 00:15:56,390 And that position in space matches the area 248 00:15:56,390 --> 00:16:02,270 where the visual input is also triggering closer 249 00:16:02,270 --> 00:16:03,050 to the surface. 250 00:16:03,050 --> 00:16:05,480 The auditory input is coming in to the middle layers 251 00:16:05,480 --> 00:16:07,360 of the colliculus. 252 00:16:07,360 --> 00:16:10,630 Somatosensory inputs are coming into the deeper layers, 253 00:16:10,630 --> 00:16:14,190 most of them below the auditory. 254 00:16:14,190 --> 00:16:17,790 And there you get a spatial map, too. 255 00:16:17,790 --> 00:16:23,520 Think of the coverage of the field around the animal's head 256 00:16:23,520 --> 00:16:29,440 by those enormous whiskers, the mystacial vibrissae of rodents. 257 00:16:29,440 --> 00:16:32,340 They protrude out into the visual field. 258 00:16:32,340 --> 00:16:34,200 So yeah, you're only dealing with the space 259 00:16:34,200 --> 00:16:35,820 right next to the head. 260 00:16:35,820 --> 00:16:42,000 But that still matches the things they see beyond that. 261 00:16:42,000 --> 00:16:45,710 So they can anticipate something coming at them. 262 00:16:45,710 --> 00:16:47,977 They can anticipate a stimulus in the whisker 263 00:16:47,977 --> 00:16:49,310 that's located in the same area. 264 00:16:52,160 --> 00:16:56,140 And then when we deal with pattern identification, 265 00:16:56,140 --> 00:17:00,020 that pathway from the dorsal cochlear nucleus 266 00:17:00,020 --> 00:17:03,870 goes directly to the thalamus, also 267 00:17:03,870 --> 00:17:05,600 by way of the inferior colliculus. 268 00:17:05,600 --> 00:17:09,000 But some of them go directly, and then to the endbrain. 269 00:17:09,000 --> 00:17:11,319 And most of the analysis of temporal patterns 270 00:17:11,319 --> 00:17:12,619 happens in the cortex. 271 00:17:16,359 --> 00:17:19,915 So for location, I have here the eighth nerve. 272 00:17:19,915 --> 00:17:21,539 You go to the ventral cochlear nucleus. 273 00:17:25,670 --> 00:17:31,800 And these are the structures of the trapezoid body. 274 00:17:31,800 --> 00:17:36,070 So superior olive, and that's where 275 00:17:36,070 --> 00:17:39,520 you get neurons projecting to a number of places, 276 00:17:39,520 --> 00:17:40,575 including the cerebellum. 277 00:17:40,575 --> 00:17:45,970 Even though the cerebellum. does get some direct input too. 278 00:17:45,970 --> 00:17:49,526 And then from there you go to the nuclei, 279 00:17:49,526 --> 00:17:51,740 the lateral lemniscus, and inferior colliculus 280 00:17:51,740 --> 00:17:55,650 as we'll see, and the superior colliculus. 281 00:17:55,650 --> 00:18:00,770 Which itself, as we know, has projections into the lateral 282 00:18:00,770 --> 00:18:01,270 thalamus. 283 00:18:04,630 --> 00:18:08,890 So in mammals it's the medial superior olive 284 00:18:08,890 --> 00:18:12,350 which is sensitive to precise time of arrival. 285 00:18:12,350 --> 00:18:14,970 That's just representing azimuthal position. 286 00:18:14,970 --> 00:18:16,650 I mean, the timing doesn't actually 287 00:18:16,650 --> 00:18:20,500 help the animal discriminate sounds 288 00:18:20,500 --> 00:18:24,160 above the horizontal plane or below. 289 00:18:24,160 --> 00:18:26,880 They need other ways to do that. 290 00:18:26,880 --> 00:18:28,420 It's not as accurate. 291 00:18:28,420 --> 00:18:33,000 But by simple head movements they can generate cues. 292 00:18:33,000 --> 00:18:38,170 And because of the shape of the pinnae, 293 00:18:38,170 --> 00:18:41,850 the pinnae attenuate different sound frequencies differently, 294 00:18:41,850 --> 00:18:43,570 according to elevation. 295 00:18:43,570 --> 00:18:47,245 So the sound actually has a slightly different effect 296 00:18:47,245 --> 00:18:48,315 on different neurons. 297 00:18:48,315 --> 00:18:52,845 And that is used in localization in the vertical plane. 298 00:18:52,845 --> 00:18:58,440 That's been studied in owls, where just the configuration 299 00:18:58,440 --> 00:19:02,540 of the feathers around the ears create those differences. 300 00:19:02,540 --> 00:19:04,030 I don't know as much about that. 301 00:19:04,030 --> 00:19:06,256 It's not been as well studied. 302 00:19:06,256 --> 00:19:12,120 But we do know that there is a map in the vertical dimension 303 00:19:12,120 --> 00:19:14,610 as well as in the azimuthal direction. 304 00:19:17,490 --> 00:19:19,680 So let me go through those studies in chickens. 305 00:19:24,920 --> 00:19:27,130 We've talked about this endbulb. 306 00:19:27,130 --> 00:19:32,220 That is here in this diagram of one neuron 307 00:19:32,220 --> 00:19:37,220 type on both sides in the cochlear 308 00:19:37,220 --> 00:19:39,130 nucleus of the chicken. 309 00:19:39,130 --> 00:19:42,150 So here's the axon coming in from the organ of Corti 310 00:19:42,150 --> 00:19:46,712 in the cochlea on the left side, and then on the right side. 311 00:19:46,712 --> 00:19:48,170 Here's the endbulb of Held. 312 00:19:50,880 --> 00:19:56,060 So we know every action potential coming in here 313 00:19:56,060 --> 00:19:57,090 leads to one here. 314 00:19:57,090 --> 00:20:00,080 And note that these neurons have two projections. 315 00:20:00,080 --> 00:20:01,320 They branch. 316 00:20:01,320 --> 00:20:06,444 One goes to this nucleus laminaris. 317 00:20:06,444 --> 00:20:11,270 Obvious why it gets that name, because of its appearance. 318 00:20:11,270 --> 00:20:16,000 And then the other branch goes this way, 319 00:20:16,000 --> 00:20:19,170 goes to the ventral dendrites of the nucleus 320 00:20:19,170 --> 00:20:21,250 laminaris on the other side. 321 00:20:21,250 --> 00:20:24,806 So this side, it projects to the dorsal dendrites. 322 00:20:24,806 --> 00:20:26,735 The ones on the other side project 323 00:20:26,735 --> 00:20:28,830 to the ventral dendrites. 324 00:20:28,830 --> 00:20:32,420 These cells will fire only if they 325 00:20:32,420 --> 00:20:36,040 get nearly simultaneous arrival of potentials 326 00:20:36,040 --> 00:20:39,690 from the two ears, from the two sides, 327 00:20:39,690 --> 00:20:49,885 from that cell pipe of nucleus magnocellularis on both 328 00:20:49,885 --> 00:20:53,500 the left and right sides. 329 00:20:53,500 --> 00:20:58,375 And I've noticed, when I've looked at the pictures in Golgi 330 00:20:58,375 --> 00:21:03,370 in a study of the chick-- this was 331 00:21:03,370 --> 00:21:06,840 Jhaveri and Morest at Harvard. 332 00:21:06,840 --> 00:21:10,510 They studied the development of this system, 333 00:21:10,510 --> 00:21:13,450 including the development of these big endbulbs. 334 00:21:13,450 --> 00:21:18,460 But they also pictured the magnocellularis cells. 335 00:21:18,460 --> 00:21:22,910 And I've noticed that always the cells didn't go directly 336 00:21:22,910 --> 00:21:24,660 towards laminaris. 337 00:21:24,660 --> 00:21:28,460 They made this loop. 338 00:21:28,460 --> 00:21:32,100 Obviously designed to keep the timing 339 00:21:32,100 --> 00:21:35,260 nearly the same as the crossing axon. 340 00:21:35,260 --> 00:21:40,540 Now you, of course, would have to get slight differences 341 00:21:40,540 --> 00:21:44,170 in the length of the axon. 342 00:21:44,170 --> 00:21:46,100 That would be the simplest way, anyway, 343 00:21:46,100 --> 00:21:49,260 to get different positions in space. 344 00:21:49,260 --> 00:21:51,240 The studies that have been published 345 00:21:51,240 --> 00:21:54,760 indicate that this one is kept more constant. 346 00:21:54,760 --> 00:21:56,885 And the crossing one is the one that 347 00:21:56,885 --> 00:21:59,320 varies a little bit systematically. 348 00:21:59,320 --> 00:22:06,520 So the result is a map of the azimuthal plane 349 00:22:06,520 --> 00:22:13,710 from directly to the left to right in front, 350 00:22:13,710 --> 00:22:18,200 and then on the other side to the other side. 351 00:22:18,200 --> 00:22:20,180 So you get the whole field represented 352 00:22:20,180 --> 00:22:24,990 only if you take both nuclei into account. 353 00:22:24,990 --> 00:22:31,070 So there is no laminaris in the mammalian brain. 354 00:22:31,070 --> 00:22:40,040 But the lateral superior olive contains cells just like this. 355 00:22:40,040 --> 00:22:43,840 It was all more theoretical. 356 00:22:43,840 --> 00:22:47,600 It was theory for a long time. 357 00:22:47,600 --> 00:22:50,450 And the reason I use the chick studies 358 00:22:50,450 --> 00:22:52,490 is because that's where they finally 359 00:22:52,490 --> 00:22:55,830 were able to pin it down and make measures. 360 00:22:55,830 --> 00:22:59,720 It was done by, that anatomical study I was telling you about 361 00:22:59,720 --> 00:23:03,397 by Jhaveri and Morest at the same time Tom Parks out 362 00:23:03,397 --> 00:23:04,980 of the University of Utah was studying 363 00:23:04,980 --> 00:23:08,630 the electrophysiology of that system in the chicks. 364 00:23:08,630 --> 00:23:10,836 And together they made a very powerful story. 365 00:23:15,620 --> 00:23:18,030 And one of the places these axons project 366 00:23:18,030 --> 00:23:20,735 is to the tectum of the midbrain. 367 00:23:24,360 --> 00:23:26,810 This is just speculation about how it evolved. 368 00:23:26,810 --> 00:23:31,870 You can read it if you're curious about that. 369 00:23:31,870 --> 00:23:38,210 There is a second mechanism for sound localization involving, 370 00:23:38,210 --> 00:23:40,270 in mammals, the lateral superior olive. 371 00:23:40,270 --> 00:23:44,990 Did I say, I think I was supposed to say medial before. 372 00:23:44,990 --> 00:23:46,480 This one's the lateral. 373 00:23:46,480 --> 00:23:48,840 And that's responsive to differences 374 00:23:48,840 --> 00:23:50,930 in amplitude of the two ears. 375 00:23:50,930 --> 00:23:53,560 Because, of course, that's an even simpler way. 376 00:23:53,560 --> 00:23:56,880 Obviously sound is going to be louder 377 00:23:56,880 --> 00:23:59,390 because the head's in the way of the other ear. 378 00:23:59,390 --> 00:24:02,510 So there is a slight difference in intensity, too. 379 00:24:02,510 --> 00:24:04,010 So that is also used. 380 00:24:04,010 --> 00:24:08,260 But it's decoded in the lateral superior olive. 381 00:24:08,260 --> 00:24:11,510 And I don't know how that's handled in chicks. 382 00:24:11,510 --> 00:24:15,017 Because the study in chicks was focused on that nucleus 383 00:24:15,017 --> 00:24:16,850 that they could get to with their electrodes 384 00:24:16,850 --> 00:24:19,462 and find it in animal after animal, 385 00:24:19,462 --> 00:24:22,470 because it was located right dorsally. 386 00:24:22,470 --> 00:24:26,780 This is all in the dorsal hindbrain of the chick. 387 00:24:26,780 --> 00:24:29,180 This is hard to get at in the mammal, 388 00:24:29,180 --> 00:24:31,810 because it's way down ventrally in the hindbrain. 389 00:24:31,810 --> 00:24:33,260 And they're very small nuclei. 390 00:24:33,260 --> 00:24:36,024 So it's difficult to do the study in mammals. 391 00:24:42,100 --> 00:24:48,750 And then I mentioned how the owl uses different attenuation 392 00:24:48,750 --> 00:24:51,200 and different frequencies, and how head movements-- 393 00:24:51,200 --> 00:24:53,280 we use head movements a lot. 394 00:24:53,280 --> 00:24:56,770 When we hear sounds we may not even think about it sometimes. 395 00:24:56,770 --> 00:24:58,710 But we make slight movements of the heads. 396 00:24:58,710 --> 00:25:01,800 And we know this improves our localization ability. 397 00:25:05,030 --> 00:25:06,870 Let's answer these questions. 398 00:25:06,870 --> 00:25:09,210 Distinguish between two prominent pathways 399 00:25:09,210 --> 00:25:11,240 to the auditory system. 400 00:25:11,240 --> 00:25:13,390 The lateral lemniscus and the breaking 401 00:25:13,390 --> 00:25:16,680 of the inferior [INAUDIBLE]. 402 00:25:16,680 --> 00:25:20,670 So I brought this picture from the [INAUDIBLE] system chapter. 403 00:25:20,670 --> 00:25:22,090 You can see those. 404 00:25:22,090 --> 00:25:24,230 Here is the lateral lemniscus. 405 00:25:24,230 --> 00:25:27,010 You see the white there. 406 00:25:27,010 --> 00:25:30,370 It's the axons coming, they're actually 407 00:25:30,370 --> 00:25:32,570 mostly coming from down here. 408 00:25:32,570 --> 00:25:37,570 This bump here is the superior olive. 409 00:25:37,570 --> 00:25:42,950 The bump for the caudal here is the inferior olive. 410 00:25:42,950 --> 00:25:44,790 The superior olive is the auditory pathway. 411 00:25:48,010 --> 00:25:50,590 And it includes the trapezoid body cells here. 412 00:25:53,760 --> 00:25:55,030 I should start here. 413 00:25:55,030 --> 00:25:57,880 You see the cochlea nucleus there? 414 00:25:57,880 --> 00:26:00,780 And you see that little-- that's a nerve there. 415 00:26:00,780 --> 00:26:03,256 Here come the axons. 416 00:26:03,256 --> 00:26:06,590 I've drawn an arrow to the cochlear nucleus. 417 00:26:06,590 --> 00:26:11,525 And there you go down to the trapezoid body 418 00:26:11,525 --> 00:26:14,080 in the superior olive. 419 00:26:14,080 --> 00:26:18,220 And then here you have pathways going 420 00:26:18,220 --> 00:26:19,540 to the inferior colliculus. 421 00:26:19,540 --> 00:26:23,710 Some of them end a little before they get there, 422 00:26:23,710 --> 00:26:26,932 in the nuclei of the trapezoid body. 423 00:26:26,932 --> 00:26:29,990 They follow that lateral lemniscus up. 424 00:26:29,990 --> 00:26:34,980 And then from there they follow-- 425 00:26:34,980 --> 00:26:41,580 I drew it a little too far, I guess-- they go into that bump. 426 00:26:41,580 --> 00:26:45,730 This is the breaking of the inferior colliculus. 427 00:26:49,120 --> 00:26:54,320 You look carefully, you do see deeper shadows on either side. 428 00:26:54,320 --> 00:26:56,770 It is a white band there. 429 00:26:56,770 --> 00:27:02,210 So we're talking about then lateral lemniscus here, 430 00:27:02,210 --> 00:27:05,812 breaking the inferior colliculus here in blue. 431 00:27:05,812 --> 00:27:09,680 I've labelled those different components in different colors. 432 00:27:09,680 --> 00:27:13,980 And that picture is in color in your book. 433 00:27:13,980 --> 00:27:17,020 But I wanted you to see that once you learn that anatomy, 434 00:27:17,020 --> 00:27:19,260 you can make these things out just looking 435 00:27:19,260 --> 00:27:20,500 at the surface of the brain. 436 00:27:20,500 --> 00:27:25,532 And it varies a lot, depending on how you adjust the light. 437 00:27:25,532 --> 00:27:27,115 If you're working with another species 438 00:27:27,115 --> 00:27:29,655 and you want to get a picture like this, 439 00:27:29,655 --> 00:27:33,160 just get a really well-fixed brain, 440 00:27:33,160 --> 00:27:35,630 clear the surface of all the blood vessels, 441 00:27:35,630 --> 00:27:37,310 and just play with the light. 442 00:27:37,310 --> 00:27:42,010 And you'll end up seeing all these different things. 443 00:27:42,010 --> 00:27:45,230 So here we can see all the auditory system things. 444 00:27:47,870 --> 00:27:50,650 I'll put that online with one without the arrows and one 445 00:27:50,650 --> 00:27:52,099 with the arrows. 446 00:27:58,540 --> 00:28:03,430 Where does information about location of sounds and sights 447 00:28:03,430 --> 00:28:09,160 converge in the subcortical structures of the CNS? 448 00:28:09,160 --> 00:28:11,506 Where would that be? 449 00:28:11,506 --> 00:28:17,210 I was talking about visual, auditory, somatosensory, 450 00:28:17,210 --> 00:28:20,220 all in optic tectum or superior colliculus. 451 00:28:20,220 --> 00:28:23,210 Then I say what happens that the auditory and visual get out 452 00:28:23,210 --> 00:28:25,410 of register? 453 00:28:25,410 --> 00:28:27,220 How could that happen? 454 00:28:27,220 --> 00:28:30,120 Well, it happens with development. 455 00:28:30,120 --> 00:28:36,240 As the head changes size that happens naturally. 456 00:28:36,240 --> 00:28:39,580 If you put prisms on an animal you 457 00:28:39,580 --> 00:28:41,550 cause the visual field to shift. 458 00:28:44,240 --> 00:28:49,320 The map of the retina in the tectum doesn't change. 459 00:28:49,320 --> 00:28:52,956 What changes is the auditory map. 460 00:28:52,956 --> 00:28:56,340 The auditory map is the more plastic one. 461 00:28:56,340 --> 00:29:03,265 It shifts so it matches the visual one. 462 00:29:03,265 --> 00:29:09,125 A fascinating finding, initially by Mark Konishi in owls. 463 00:29:11,680 --> 00:29:17,330 He had prisms on the owls and he showed these effects. 464 00:29:17,330 --> 00:29:19,680 But we should have realized something 465 00:29:19,680 --> 00:29:22,100 like that had to be happening in development. 466 00:29:22,100 --> 00:29:23,930 It would be very difficult. 467 00:29:23,930 --> 00:29:26,560 It's similar to what the cerebellum does, 468 00:29:26,560 --> 00:29:29,245 for timing and controlling the motor system. 469 00:29:29,245 --> 00:29:31,601 But here it's in the sensory system. 470 00:29:38,200 --> 00:29:41,190 So then in question nine here, I say characterize 471 00:29:41,190 --> 00:29:43,760 two separate functions of auditory system pathways 472 00:29:43,760 --> 00:29:46,280 extending through the brainstem. 473 00:29:46,280 --> 00:29:48,680 How is the separation of these two functions 474 00:29:48,680 --> 00:29:51,480 expressed from the endbrain? 475 00:29:51,480 --> 00:29:53,791 Even in transcortical pathways. 476 00:29:53,791 --> 00:29:57,660 Now that requires you to read a lot more of the chapter 477 00:29:57,660 --> 00:29:59,260 to get all those parts. 478 00:29:59,260 --> 00:30:01,110 But what am I talking about? 479 00:30:01,110 --> 00:30:02,026 AUDIENCE: [INAUDIBLE]. 480 00:30:06,250 --> 00:30:08,060 PROFESSOR: So the location information 481 00:30:08,060 --> 00:30:09,730 is what we were just talking about. 482 00:30:09,730 --> 00:30:12,470 That's one of the functions. 483 00:30:12,470 --> 00:30:16,080 But what's the other major function? 484 00:30:16,080 --> 00:30:19,758 And the pathways are largely different. 485 00:30:19,758 --> 00:30:21,220 AUDIENCE: Identifying. 486 00:30:21,220 --> 00:30:24,790 PROFESSOR: Identifying auditory stimuli, 487 00:30:24,790 --> 00:30:27,700 which is done mainly by patterns. 488 00:30:27,700 --> 00:30:30,550 Because it can't be just frequency, right? 489 00:30:30,550 --> 00:30:34,060 I mean, if your child's voice changes, 490 00:30:34,060 --> 00:30:35,540 you want to still understand him. 491 00:30:35,540 --> 00:30:37,120 Even though he's talking in a full 492 00:30:37,120 --> 00:30:39,050 register below where he used to talk. 493 00:30:42,355 --> 00:30:48,560 So we are responding to patterns, not 494 00:30:48,560 --> 00:30:51,670 to absolute frequencies. 495 00:30:51,670 --> 00:30:55,750 We respond to amplitude changes, and that might be important. 496 00:30:55,750 --> 00:30:58,970 But not nearly as important as temporal patterns 497 00:30:58,970 --> 00:31:04,245 and frequency, various kinds of complex frequency modulation. 498 00:31:13,190 --> 00:31:17,270 I mentioned the experiments on location information 499 00:31:17,270 --> 00:31:20,520 getting to the colliculus. 500 00:31:20,520 --> 00:31:24,130 And here let me just add to that the studies of ablation 501 00:31:24,130 --> 00:31:27,180 of superior colliculus. 502 00:31:27,180 --> 00:31:29,090 These were done by me in the hamster. 503 00:31:29,090 --> 00:31:32,750 But they've then been done extensively in the cat as well. 504 00:31:32,750 --> 00:31:35,300 Lesions don't just affect visual orienting. 505 00:31:35,300 --> 00:31:38,050 They affect auditory orienting. 506 00:31:38,050 --> 00:31:40,990 And they affect, more transiently, 507 00:31:40,990 --> 00:31:42,910 somatosensory orienting, too. 508 00:31:42,910 --> 00:31:46,930 The somatosensory recovers the best, even 509 00:31:46,930 --> 00:31:48,390 without the colliculus. 510 00:31:51,360 --> 00:31:56,130 Why do you think it's just transiently affected? 511 00:31:56,130 --> 00:31:58,040 These are diaschisis effects. 512 00:31:58,040 --> 00:31:59,730 Tectum is big. 513 00:31:59,730 --> 00:32:02,865 And it's affecting brain stem mechanisms 514 00:32:02,865 --> 00:32:05,190 for orienting as well. 515 00:32:05,190 --> 00:32:09,705 So initially you get the loss of the input from that big tectum. 516 00:32:09,705 --> 00:32:10,580 They lose everything. 517 00:32:13,670 --> 00:32:15,800 They're amazing animals when they first 518 00:32:15,800 --> 00:32:17,470 wake up from the surgery. 519 00:32:17,470 --> 00:32:19,290 They can't orient to anything. 520 00:32:21,930 --> 00:32:23,140 Then they recover. 521 00:32:23,140 --> 00:32:27,565 They pretty soon are responding to their whiskers again. 522 00:32:27,565 --> 00:32:28,981 AUDIENCE: What does their behavior 523 00:32:28,981 --> 00:32:33,280 look like when they can't orient to anything? 524 00:32:33,280 --> 00:32:35,690 PROFESSOR: They're hunched up in the corner, 525 00:32:35,690 --> 00:32:38,300 but they are hungry. 526 00:32:38,300 --> 00:32:41,010 So the first thing they start responding to 527 00:32:41,010 --> 00:32:44,040 is stimulation around the lips. 528 00:32:44,040 --> 00:32:47,810 And then they start orienting to touches around the lips, 529 00:32:47,810 --> 00:32:50,010 around the mouth. 530 00:32:50,010 --> 00:32:51,740 They will start turning a little bit, 531 00:32:51,740 --> 00:32:55,210 so they can see you're trying to feed them. 532 00:32:55,210 --> 00:32:57,610 These are the hamsters. 533 00:32:57,610 --> 00:32:59,940 Big advantage to using hamsters is 534 00:32:59,940 --> 00:33:04,810 they're so motivated to get those little seeds, you know. 535 00:33:04,810 --> 00:33:09,194 And they're also a lot cuter than rats and mice. 536 00:33:09,194 --> 00:33:10,610 AUDIENCE: I don't know about that. 537 00:33:10,610 --> 00:33:13,480 PROFESSOR: They're fun to study. 538 00:33:13,480 --> 00:33:18,910 [LAUGHTER] 539 00:33:18,910 --> 00:33:22,450 The deficits in orienting towards sounds 540 00:33:22,450 --> 00:33:26,986 recovers a little bit to laterally placed sounds. 541 00:33:26,986 --> 00:33:29,345 There are hindbrain mechanisms that 542 00:33:29,345 --> 00:33:32,130 can turn the head in response to sounds, even 543 00:33:32,130 --> 00:33:33,380 without the tectum. 544 00:33:33,380 --> 00:33:35,600 It's wiped out at the beginning. 545 00:33:35,600 --> 00:33:38,810 That then has a slower recovery than the somatosensory 546 00:33:38,810 --> 00:33:40,850 orienting, but it recovers. 547 00:33:40,850 --> 00:33:44,420 But the orienting to overhead stimuli 548 00:33:44,420 --> 00:33:47,310 is very dependent on the tectum. 549 00:33:47,310 --> 00:33:51,760 And they just don't orient to things above them. 550 00:33:51,760 --> 00:33:55,810 They can show freezing responses to novel sounds. 551 00:33:55,810 --> 00:33:58,410 Because they're detecting them with the cortex. 552 00:33:58,410 --> 00:34:00,880 It's just making those movements that has changed. 553 00:34:07,920 --> 00:34:15,270 And we have a lot of information on the pathways cortex, 554 00:34:15,270 --> 00:34:19,674 location information, auditory localization of sounds 555 00:34:19,674 --> 00:34:24,290 does reach the cortex as well. 556 00:34:24,290 --> 00:34:28,650 In fact, they've shown distinct cortical regions reached 557 00:34:28,650 --> 00:34:33,989 by location information and identification information 558 00:34:33,989 --> 00:34:35,489 They are separate in the cortex. 559 00:34:35,489 --> 00:34:38,690 I've found there's a lot of pictures 560 00:34:38,690 --> 00:34:40,400 of this just in recent years. 561 00:34:40,400 --> 00:34:42,750 But this is a very clear one. 562 00:34:42,750 --> 00:34:44,980 Here you have the primary auditory cortex. 563 00:34:44,980 --> 00:34:47,300 And then around the auditory cortex, 564 00:34:47,300 --> 00:34:52,690 we talk about the auditory belt cortex. 565 00:34:52,690 --> 00:34:57,380 The areas here in the rostral belt cortex 566 00:34:57,380 --> 00:35:00,550 are the ones sensitive to position. 567 00:35:00,550 --> 00:35:05,460 And the projections from there go into the posterior parietal 568 00:35:05,460 --> 00:35:08,920 cortex, the same regions that are getting visual. 569 00:35:08,920 --> 00:35:12,320 It's not identical regions, they're adjacent regions. 570 00:35:12,320 --> 00:35:14,380 But then there are regions of convergence, too. 571 00:35:17,500 --> 00:35:22,770 The picture here doesn't show the convergence. 572 00:35:22,770 --> 00:35:25,870 And then from these regions, you have the pathways 573 00:35:25,870 --> 00:35:27,890 going to prefrontal cortex. 574 00:35:27,890 --> 00:35:34,040 We talked about those for the visual system earlier. 575 00:35:34,040 --> 00:35:36,170 Same thing happens for audition. 576 00:35:36,170 --> 00:35:39,781 It goes right into those areas of the frontal eye fields. 577 00:35:39,781 --> 00:35:45,030 So it's getting not just visual, but auditory as well. 578 00:35:45,030 --> 00:35:47,690 And some of the pathways don't even 579 00:35:47,690 --> 00:35:49,650 go through posterior or parietal. 580 00:35:49,650 --> 00:35:52,500 They go directly to prefrontal. 581 00:35:52,500 --> 00:35:58,660 And then in the rostral auditory belt cortex, 582 00:35:58,660 --> 00:36:03,980 you have pathways leading through the superior temporal 583 00:36:03,980 --> 00:36:07,230 gyrus to the amygdala. 584 00:36:07,230 --> 00:36:10,830 And from the temporal pole directly 585 00:36:10,830 --> 00:36:15,080 to the ventral prefrontal areas. 586 00:36:15,080 --> 00:36:17,610 Those same areas that themselves project 587 00:36:17,610 --> 00:36:19,280 to amygdala and hypothalamus. 588 00:36:22,130 --> 00:36:26,555 So they show here how the visual pathways do a similar thing 589 00:36:26,555 --> 00:36:32,300 as we talked about in chapter 22. 590 00:36:37,050 --> 00:36:41,750 It was years after the discovery of the visual system 591 00:36:41,750 --> 00:36:45,260 pathways like that where people started paying attention 592 00:36:45,260 --> 00:36:47,052 to this in the auditory system. 593 00:36:47,052 --> 00:36:48,770 And then this was worked out. 594 00:36:52,060 --> 00:36:55,026 Let's talk about auditory pattern detection. 595 00:36:55,026 --> 00:36:58,430 We still have a little time. 596 00:36:58,430 --> 00:37:03,180 Now we're talking more about dorsal cochlear nucleus. 597 00:37:03,180 --> 00:37:05,980 That's where you have their origins of the most 598 00:37:05,980 --> 00:37:07,590 direct pathways. 599 00:37:07,590 --> 00:37:13,410 These are temporal information in the auditory input. 600 00:37:13,410 --> 00:37:18,160 It goes to main nucleus of the medial geniculate body. 601 00:37:18,160 --> 00:37:21,010 And from there through the auditory area primarily. 602 00:37:24,480 --> 00:37:28,410 So when they map auditory cortex by physiology-- 603 00:37:28,410 --> 00:37:31,890 there are beautiful anatomical maps too. 604 00:37:31,890 --> 00:37:34,560 Even the Golgi studies have seen this. 605 00:37:34,560 --> 00:37:37,280 The way neurons are arranged in both inferior colliculus 606 00:37:37,280 --> 00:37:42,960 and medial geniculate body is a very well organized system. 607 00:37:42,960 --> 00:37:45,350 When you get up to cortex, it's been the physiologists 608 00:37:45,350 --> 00:37:46,650 that have dominated the field. 609 00:37:46,650 --> 00:37:50,370 And now we have physiologists studying the auditory system--d 610 00:37:50,370 --> 00:37:53,780 Josh McDermott here in the department. 611 00:37:53,780 --> 00:37:55,930 And they've mapped these. 612 00:37:55,930 --> 00:37:59,470 Initially they looked for the tonotopic maps, 613 00:37:59,470 --> 00:38:03,170 just like in the cochlear nuclei. 614 00:38:03,170 --> 00:38:06,550 We already know that animals can discriminate 615 00:38:06,550 --> 00:38:10,266 different frequencies without the cortex. 616 00:38:15,740 --> 00:38:17,770 So I'm asking here in this question, 617 00:38:17,770 --> 00:38:20,625 describe several properties that have enabled investigators 618 00:38:20,625 --> 00:38:24,940 to distinguish multiple neocortical auditory areas. 619 00:38:24,940 --> 00:38:29,290 The first one is frequency differences. 620 00:38:33,070 --> 00:38:34,590 A1 is a good illustration. 621 00:38:34,590 --> 00:38:37,850 But these are different positions, 622 00:38:37,850 --> 00:38:40,460 from rostral to caudal, different distances 623 00:38:40,460 --> 00:38:43,460 from the posterior suprasylvian sulcus. 624 00:38:43,460 --> 00:38:47,560 Here's the posterior suprasylvian sulcus. 625 00:38:47,560 --> 00:38:51,070 Here's the middle suprasylvian, here's the anterior. 626 00:38:51,070 --> 00:38:54,960 So they measure from here, and they go across this cortex 627 00:38:54,960 --> 00:38:57,360 in in A1. 628 00:38:57,360 --> 00:39:01,720 And when they do that, at each position 629 00:39:01,720 --> 00:39:04,030 they find multiple best frequencies. 630 00:39:04,030 --> 00:39:05,876 That is the frequency where you get 631 00:39:05,876 --> 00:39:07,640 the best responses in that neuron. 632 00:39:07,640 --> 00:39:10,420 The neuron does respond, though, to other frequencies, too. 633 00:39:10,420 --> 00:39:12,840 It's just that it's most sensitive at one frequency. 634 00:39:12,840 --> 00:39:14,805 So they use that for these maps. 635 00:39:18,650 --> 00:39:21,540 But you can see that the envelope 636 00:39:21,540 --> 00:39:26,870 of the planes in this kind of graph 637 00:39:26,870 --> 00:39:30,770 do show up on a tonotopic map. 638 00:39:30,770 --> 00:39:34,430 It does respond to higher frequencies 639 00:39:34,430 --> 00:39:37,340 when you're further from the posterior suprasylvian sulcus. 640 00:39:37,340 --> 00:39:40,740 So that's what a tonotopic map is in the auditory system. 641 00:39:40,740 --> 00:39:44,420 It doesn't mean it's a precise map. 642 00:39:44,420 --> 00:39:47,820 At any one position, you can get a lot of different frequencies. 643 00:39:47,820 --> 00:39:50,580 And there is a reason for that. 644 00:39:50,580 --> 00:39:53,425 It uses that information from other frequencies. 645 00:39:56,700 --> 00:39:59,790 So here in the cat, which is by far the best 646 00:39:59,790 --> 00:40:02,440 studied animal for auditory system. 647 00:40:02,440 --> 00:40:07,050 And Jeff Winer, who I know and was working with Kent Morest, 648 00:40:07,050 --> 00:40:11,930 the guy that did a lot of that work on the auditory system 649 00:40:11,930 --> 00:40:14,910 at Harvard, and Jhaveri was his student there. 650 00:40:17,730 --> 00:40:20,640 Winer worked with Morest in anatomy, 651 00:40:20,640 --> 00:40:24,830 and then also did a lot of physiology. 652 00:40:24,830 --> 00:40:28,040 And this is from one of his review papers. 653 00:40:28,040 --> 00:40:31,890 He describes five tonotopic maps. 654 00:40:31,890 --> 00:40:38,202 And you see them here-- one, two, three, four, five. 655 00:40:38,202 --> 00:40:41,670 This light gray area in the picture. 656 00:40:41,670 --> 00:40:44,850 They all have this frequency difference 657 00:40:44,850 --> 00:40:47,600 when you go from one position to the other. 658 00:40:47,600 --> 00:40:52,230 Then there are three nontonotopic areas. 659 00:40:52,230 --> 00:40:54,090 They are the darker gray here. 660 00:40:57,620 --> 00:41:01,070 This is anterior ectosylvian, and what 661 00:41:01,070 --> 00:41:03,275 we call auditory area two. 662 00:41:03,275 --> 00:41:05,095 So what does it respond to? 663 00:41:07,830 --> 00:41:09,950 Well, just like auditory cortex, it 664 00:41:09,950 --> 00:41:13,390 responds to frequency modulation of tones. 665 00:41:13,390 --> 00:41:15,820 And then there's three multisensory areas. 666 00:41:15,820 --> 00:41:17,565 So they're not just auditory. 667 00:41:17,565 --> 00:41:19,940 They're really association areas. 668 00:41:19,940 --> 00:41:20,840 And they're these. 669 00:41:23,520 --> 00:41:27,800 Not the auditory system, people, they're really 670 00:41:27,800 --> 00:41:30,170 multisensory areas. 671 00:41:30,170 --> 00:41:32,700 The visual areas are here. 672 00:41:32,700 --> 00:41:37,110 And unimodal visual areas, association areas, are in here. 673 00:41:37,110 --> 00:41:40,850 [INAUDIBLE] areas in this lateral gyrus. 674 00:41:40,850 --> 00:41:43,330 It's very peculiar in that they call it lateral 675 00:41:43,330 --> 00:41:46,630 gyrus when it's the most medial gyrus in the hemisphere. 676 00:41:46,630 --> 00:41:47,590 It's this gyrus. 677 00:41:50,810 --> 00:41:53,860 And these are the unimodal association areas. 678 00:41:53,860 --> 00:41:56,450 And then multimodal areas. 679 00:41:56,450 --> 00:42:00,335 And then there's two limbic areas. 680 00:42:00,335 --> 00:42:05,690 We call it the insular cortex. 681 00:42:05,690 --> 00:42:09,970 It corresponds to insular in the monkey and humans. 682 00:42:09,970 --> 00:42:12,610 And this temporal area here. 683 00:42:15,360 --> 00:42:19,800 This area is covering that area where the amygdala is located, 684 00:42:19,800 --> 00:42:21,530 by this neocortical area. 685 00:42:21,530 --> 00:42:23,230 It's not part of the amygdala. 686 00:42:23,230 --> 00:42:25,000 They are near cortical areas. 687 00:42:29,360 --> 00:42:30,810 And then I mention here, there is 688 00:42:30,810 --> 00:42:34,972 separation of input from the two ears in the cortex. 689 00:42:39,410 --> 00:42:41,330 And then I ask about ablation effects. 690 00:42:41,330 --> 00:42:43,765 I say how are ablation effects in the auditory cortex 691 00:42:43,765 --> 00:42:46,680 of the cat related to word deafness 692 00:42:46,680 --> 00:42:48,900 after certain cortical lesions in humans? 693 00:42:48,900 --> 00:42:54,410 Well, I like to start with the early electrophysiological 694 00:42:54,410 --> 00:42:55,860 studies. 695 00:42:55,860 --> 00:42:58,267 Because they're still the best examples of what 696 00:42:58,267 --> 00:43:01,870 we mean by pattern selectivity. 697 00:43:01,870 --> 00:43:03,360 Let's look at this one. 698 00:43:03,360 --> 00:43:06,510 I won't go over all the others, but I published some of them 699 00:43:06,510 --> 00:43:08,720 in the book. 700 00:43:08,720 --> 00:43:13,780 Here they have to one tone-- and here's 701 00:43:13,780 --> 00:43:17,320 the map of how it responds to single tones. 702 00:43:17,320 --> 00:43:18,950 Here's the sound pressure levels, 703 00:43:18,950 --> 00:43:21,660 and notice that the minimal amplitude sound, 704 00:43:21,660 --> 00:43:24,640 it's responding best at one frequency here. 705 00:43:24,640 --> 00:43:27,590 That's how they get the tonotopic maps, 706 00:43:27,590 --> 00:43:32,070 by mapping single neurons like this. 707 00:43:32,070 --> 00:43:34,450 You can do it with larger electrodes, 708 00:43:34,450 --> 00:43:40,430 too, and still get some degree of mapping. 709 00:43:40,430 --> 00:43:46,305 And notice how it responds to tone on, not to tone off. 710 00:43:46,305 --> 00:43:49,140 And it'll do that for a number of different frequencies. 711 00:43:49,140 --> 00:43:51,880 But obviously most sensitive here. 712 00:43:51,880 --> 00:43:53,830 But now look what happens if you give 713 00:43:53,830 --> 00:43:55,930 a tonal changing frequency. 714 00:43:55,930 --> 00:43:59,180 Frequency modulation, so it's going 715 00:43:59,180 --> 00:44:01,530 [WHISTLING UP AND DOWN LIKE A SIREN]. 716 00:44:01,530 --> 00:44:07,200 And it's responding always to the upward ramp of frequencies. 717 00:44:07,200 --> 00:44:11,470 And that's what we mean by temporal sensitivity. 718 00:44:11,470 --> 00:44:15,110 And there's many examples of that. 719 00:44:15,110 --> 00:44:17,090 Some of the examples are more complex. 720 00:44:17,090 --> 00:44:18,820 Like here's one that always responds 721 00:44:18,820 --> 00:44:20,260 to the offset of the tone. 722 00:44:22,890 --> 00:44:27,506 Here's one that responds best to short tone, the up 723 00:44:27,506 --> 00:44:28,885 side of short tones. 724 00:44:28,885 --> 00:44:32,766 But to longer tones, it responds much more vigorously 725 00:44:32,766 --> 00:44:35,200 when the sound goes up. 726 00:44:35,200 --> 00:44:37,700 This one doesn't respond to the long burst, 727 00:44:37,700 --> 00:44:40,360 but will respond to the short burst, 728 00:44:40,360 --> 00:44:43,820 but only after repeated presentations. 729 00:44:43,820 --> 00:44:47,220 So you get a lot of variability, always sensitive 730 00:44:47,220 --> 00:44:49,490 to temporal patterns. 731 00:44:49,490 --> 00:44:52,140 And Whitfield and Evans, who were the first to really 732 00:44:52,140 --> 00:44:55,490 comprehensively study this, have a simple model, 733 00:44:55,490 --> 00:45:00,800 which I've redrawn here to make it a little clearer, 734 00:45:00,800 --> 00:45:07,503 showing that once you have this frequency specificity 735 00:45:07,503 --> 00:45:15,030 in the cortex, by having inhibitory interneurons that 736 00:45:15,030 --> 00:45:21,740 are asymmetric in between these neurons, you can get, 737 00:45:21,740 --> 00:45:23,620 because of the inhibitory pathways, 738 00:45:23,620 --> 00:45:27,970 this neuron won't respond well when you're going high to low. 739 00:45:27,970 --> 00:45:30,280 But when you're going low to high, 740 00:45:30,280 --> 00:45:35,740 the inhibition timing will not inhibit those adjacent neurons 741 00:45:35,740 --> 00:45:39,135 in time, so you will get a response. 742 00:45:39,135 --> 00:45:43,660 And again, of course you have to assume certain convergence 743 00:45:43,660 --> 00:45:48,320 in the neuron further on in the pathway. 744 00:45:48,320 --> 00:45:50,820 But because they don't find neurons 745 00:45:50,820 --> 00:45:54,180 like this, output neurons, of the thalamus. 746 00:45:54,180 --> 00:45:55,780 You do find them in the cortex. 747 00:45:55,780 --> 00:45:57,860 You know that it's got to have circuits 748 00:45:57,860 --> 00:46:01,910 somewhat like this in the cortical areas. 749 00:46:01,910 --> 00:46:06,410 And it involves these inhibitory interneurons, 750 00:46:06,410 --> 00:46:10,510 which remember arise in mammals from noncortical areas 751 00:46:10,510 --> 00:46:11,550 in development. 752 00:46:11,550 --> 00:46:12,502 But they migrate in. 753 00:46:12,502 --> 00:46:14,335 And there's a lot of inhibitory interneurons 754 00:46:14,335 --> 00:46:18,360 there in the cortex. 755 00:46:18,360 --> 00:46:21,740 Now, if you ablate the cortex, you 756 00:46:21,740 --> 00:46:24,010 don't get rid of frequency discrimination. 757 00:46:24,010 --> 00:46:29,676 But you get profound defects in responses to patterns. 758 00:46:29,676 --> 00:46:32,200 You can train them to respond to very 759 00:46:32,200 --> 00:46:35,620 simple temporally modulated tones. 760 00:46:35,620 --> 00:46:40,300 They fail to learn it after you ablate even just a one, 761 00:46:40,300 --> 00:46:42,160 or even just a more ventral area. 762 00:46:42,160 --> 00:46:43,890 They have a terrible time. 763 00:46:43,890 --> 00:46:45,640 These are highly interconnected areas, 764 00:46:45,640 --> 00:46:50,640 so of course you're getting large diaschisis effects, too. 765 00:46:50,640 --> 00:46:53,430 A lot of these patterns appear to depend 766 00:46:53,430 --> 00:47:01,200 on these interconnections between these auditory areas. 767 00:47:01,200 --> 00:47:04,090 You can use pattern discrimination, 768 00:47:04,090 --> 00:47:08,115 you can use responses to novelty instead of habituation 769 00:47:08,115 --> 00:47:11,240 to novel sounds. 770 00:47:11,240 --> 00:47:12,980 You always get the same kind of result. 771 00:47:15,780 --> 00:47:18,860 They need the cortex to respond to temporal patterns. 772 00:47:18,860 --> 00:47:20,780 So it's like humans with word deafness. 773 00:47:20,780 --> 00:47:24,470 Words are, of course, really complex temporal patterns. 774 00:47:24,470 --> 00:47:31,180 And humans can become word deaf with cortical lesions 775 00:47:31,180 --> 00:47:33,108 that affect auditory regions. 776 00:47:37,930 --> 00:47:41,160 I point out here another species. 777 00:47:41,160 --> 00:47:44,160 Many years ago there were people, 778 00:47:44,160 --> 00:47:46,680 this was Capranica, I believe, at Cornell. 779 00:47:46,680 --> 00:47:50,430 He was studying the auditory system of bullfrogs. 780 00:47:50,430 --> 00:47:52,780 He found neurons that responded to the splash 781 00:47:52,780 --> 00:47:55,320 of another bullfrog entering the water. 782 00:47:55,320 --> 00:47:56,941 Talk about a complex pattern. 783 00:47:56,941 --> 00:47:58,905 That was a really good example. 784 00:48:01,860 --> 00:48:04,820 I tried to find his publication on that and couldn't. 785 00:48:04,820 --> 00:48:08,510 But because he talked about it a lot, 786 00:48:08,510 --> 00:48:12,910 and we talked about in here at MIT when he was doing them, 787 00:48:12,910 --> 00:48:14,530 I'm sure it was a real finding. 788 00:48:17,240 --> 00:48:20,090 There's been studies of squirrel monkeys and macaque monkeys. 789 00:48:20,090 --> 00:48:22,700 The squirrel monkey work was earlier. 790 00:48:22,700 --> 00:48:25,385 We heard a little bit about that yesterday 791 00:48:25,385 --> 00:48:28,160 from the speaker here. 792 00:48:28,160 --> 00:48:33,860 But then in 2008, using imaging methods, 793 00:48:33,860 --> 00:48:37,680 they found regions in the monkey temporal lobe that 794 00:48:37,680 --> 00:48:44,670 became active when other monkey voices were heard, 795 00:48:44,670 --> 00:48:48,510 but didn't respond to other sounds. 796 00:48:48,510 --> 00:48:51,320 Temporal patterns made by monkeys and their sounds 797 00:48:51,320 --> 00:48:54,140 was what this responded to. 798 00:48:54,140 --> 00:48:57,510 And they found that they can distinguish that area. 799 00:48:57,510 --> 00:49:01,720 It responded differently to voices in different monkeys. 800 00:49:01,720 --> 00:49:05,890 They often would get them to habituate. 801 00:49:05,890 --> 00:49:07,780 Over time it responds less. 802 00:49:07,780 --> 00:49:11,590 But then a new monkey voice appears. 803 00:49:11,590 --> 00:49:12,990 It doesn't have to be louder. 804 00:49:12,990 --> 00:49:14,470 It can even be softer. 805 00:49:14,470 --> 00:49:16,922 And suddenly that region responds again. 806 00:49:16,922 --> 00:49:21,410 So they can detect individual differences. 807 00:49:21,410 --> 00:49:24,650 I took these quotes from a news report, 808 00:49:24,650 --> 00:49:28,493 but you can find the article in Nature Neuroscience, 809 00:49:28,493 --> 00:49:32,660 from the Nikos Logothetis laboratory. 810 00:49:32,660 --> 00:49:35,176 Nikos was here working with Peter Shor 811 00:49:35,176 --> 00:49:36,902 for a while on the visual system. 812 00:49:39,700 --> 00:49:41,910 So of course we postulate that there 813 00:49:41,910 --> 00:49:44,845 are units like that in humans that respond selectively to 814 00:49:44,845 --> 00:49:45,345 [INAUDIBLE]. 815 00:49:45,345 --> 00:49:48,300 We are probably born with them, although we 816 00:49:48,300 --> 00:49:50,220 lose perhaps some of them with development 817 00:49:50,220 --> 00:49:51,740 that are not in our language. 818 00:49:55,470 --> 00:49:58,640 And we know about hemispheric differences in humans, 819 00:49:58,640 --> 00:50:03,147 too, because we specialize for dealing 820 00:50:03,147 --> 00:50:04,605 with speech in the left hemisphere. 821 00:50:07,530 --> 00:50:09,250 This is also very plastic. 822 00:50:09,250 --> 00:50:14,410 So if very early in life a child loses his left hemisphere, 823 00:50:14,410 --> 00:50:15,912 if the lesion is early enough, he 824 00:50:15,912 --> 00:50:17,745 will develop speech in the right hemisphere. 825 00:50:20,490 --> 00:50:21,930 It's very strange, though. 826 00:50:21,930 --> 00:50:24,180 If he just has a damaged left hemisphere-- 827 00:50:24,180 --> 00:50:28,280 this is not in my notes, just interesting to mention. 828 00:50:28,280 --> 00:50:33,360 If a child has damage that affects the left hemisphere, 829 00:50:33,360 --> 00:50:38,800 but it has to be totally wiped out, the hemisphere, 830 00:50:38,800 --> 00:50:41,340 to get speech to shift to the right hemisphere. 831 00:50:41,340 --> 00:50:45,200 So he'll end up with just bad speech. 832 00:50:45,200 --> 00:50:50,360 So one of the treatments for severe problems in children 833 00:50:50,360 --> 00:50:53,950 is to actually ablate the entire hemisphere. 834 00:50:53,950 --> 00:50:55,510 It sounds horrible. 835 00:50:55,510 --> 00:50:57,895 But in fact, the behavioral result 836 00:50:57,895 --> 00:51:04,170 is better if they have really bad hemisphere pathology. 837 00:51:04,170 --> 00:51:06,570 AUDIENCE: Why would that be? 838 00:51:06,570 --> 00:51:21,340 PROFESSOR: I can find-- OK. 839 00:51:21,340 --> 00:51:23,680 We'll skip over the specializations now. 840 00:51:23,680 --> 00:51:25,850 We'll mention them a little bit next time. 841 00:51:25,850 --> 00:51:29,110 They talk about echolocation a little bit. 842 00:51:29,110 --> 00:51:31,390 We saw that in chapter six. 843 00:51:31,390 --> 00:51:38,090 The structures became enlarged in bats and dolphins 844 00:51:38,090 --> 00:51:41,320 compared to the more visual animals. 845 00:51:41,320 --> 00:51:43,950 And then you should learn a little bit 846 00:51:43,950 --> 00:51:45,840 about birdsong pathways. 847 00:51:45,840 --> 00:51:47,840 Especially with Michael Fee here in the building 848 00:51:47,840 --> 00:51:50,800 studying birdsong. 849 00:51:50,800 --> 00:51:54,380 And a little bit about speech. 850 00:51:54,380 --> 00:51:58,470 And the pathways are very parallel, 851 00:51:58,470 --> 00:52:03,090 although the names are different in reptiles and birds 852 00:52:03,090 --> 00:52:04,230 than they are in mammals. 853 00:52:04,230 --> 00:52:07,132 But they have very clear regions of the endbrain that 854 00:52:07,132 --> 00:52:12,390 are auditory, just like the auditory cortex of the mammal. 855 00:52:12,390 --> 00:52:15,910 So we'll look at that briefly next time.