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 --> 00:00:10,740 to offer high quality educational resources for free. 5 00:00:10,740 --> 00:00:13,360 To make a donation or view additional materials 6 00:00:13,360 --> 00:00:17,169 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:17,169 --> 00:00:17,793 at ocw@mit.edu. 8 00:00:23,180 --> 00:00:27,880 PROFESSOR: OK, I hadn't talked yet about topography, 9 00:00:27,880 --> 00:00:32,530 and I-- even though-- I just want you to understand 10 00:00:32,530 --> 00:00:38,110 how the optic tract is laid out, and-- but before we do that, 11 00:00:38,110 --> 00:00:42,580 I'll show you midbrain of a few different species. 12 00:00:42,580 --> 00:00:45,700 There's one that occurred earlier in the book-- 13 00:00:45,700 --> 00:00:52,515 I think it was chapter 11, yes, where I compared rodent, human, 14 00:00:52,515 --> 00:00:56,180 and tree shrew, where you see these-- chapter 11 15 00:00:56,180 --> 00:00:57,405 was the midbrain chapter. 16 00:01:00,880 --> 00:01:04,640 And you can see how the size of the tectum and the size 17 00:01:04,640 --> 00:01:08,360 of the peduncle are what's so different in these three 18 00:01:08,360 --> 00:01:09,605 species. 19 00:01:09,605 --> 00:01:14,220 The humans are the huge peduncle, and aspera colliculus 20 00:01:14,220 --> 00:01:16,200 that's not so huge. 21 00:01:16,200 --> 00:01:19,660 Even though we're very visual, we 22 00:01:19,660 --> 00:01:22,860 depend a lot more on the geniculate striate system, 23 00:01:22,860 --> 00:01:26,260 because we depend more on learning. 24 00:01:26,260 --> 00:01:29,420 Whereas the tree shrew and squirrel 25 00:01:29,420 --> 00:01:32,690 would be very similar, and much more dependent 26 00:01:32,690 --> 00:01:36,070 on inmate visual reactions. 27 00:01:36,070 --> 00:01:37,470 And they have the huge tectum. 28 00:01:40,950 --> 00:01:44,970 These are some of the questions. 29 00:01:44,970 --> 00:01:48,700 I asked you to describe four different anatomical methods 30 00:01:48,700 --> 00:01:53,580 that can be used to uncover the layers of the optic tectum. 31 00:01:56,220 --> 00:02:00,400 And of course, I just meat-- just stains of normal material, 32 00:02:00,400 --> 00:02:04,200 like fiber stains and cell stains. 33 00:02:04,200 --> 00:02:08,680 You could name any fiber stain, and of course, Nissl stains 34 00:02:08,680 --> 00:02:10,860 come in a number of varieties. 35 00:02:10,860 --> 00:02:12,910 But also there's histochemical stains, 36 00:02:12,910 --> 00:02:16,410 and I showed you some of those in the methods chapter, chapter 37 00:02:16,410 --> 00:02:17,790 two. 38 00:02:17,790 --> 00:02:20,280 And then, of course, the Golgi. 39 00:02:20,280 --> 00:02:24,200 So we'll look at that just briefly today. 40 00:02:24,200 --> 00:02:27,160 You should also know a little bit about these species 41 00:02:27,160 --> 00:02:31,910 varieties, and what are the animals with the huge tectum? 42 00:02:31,910 --> 00:02:37,165 It's not only the non-mammalians, like the fish, 43 00:02:37,165 --> 00:02:40,310 and some reptiles, the visual reptiles. 44 00:02:40,310 --> 00:02:43,290 I'm sure that the dinosaurs had a very large tectum. 45 00:02:48,160 --> 00:02:53,255 And why is the term optic tectum a misleading term? 46 00:02:53,255 --> 00:02:53,755 Yes? 47 00:02:58,090 --> 00:02:59,600 They're so loud in here, you have 48 00:02:59,600 --> 00:03:10,930 to-- but it could still be an optic tectum. 49 00:03:10,930 --> 00:03:14,360 It's optic that's not accurate. 50 00:03:14,360 --> 00:03:20,265 It's just the superficial layers that get the visual input 51 00:03:20,265 --> 00:03:23,220 from this optic or visual sense. 52 00:03:23,220 --> 00:03:26,270 It gets them at a sensory and auditory input as well, 53 00:03:26,270 --> 00:03:28,290 and it gets cerebellar input. 54 00:03:28,290 --> 00:03:32,760 OK, so especially all that auditory and meta sensory input 55 00:03:32,760 --> 00:03:37,760 coming in there, it's a lot more than just in the tectum. 56 00:03:37,760 --> 00:03:40,430 So sometimes I call it a correlation center. 57 00:03:40,430 --> 00:03:47,900 It brings in all these different modalities that kind of all 58 00:03:47,900 --> 00:03:50,980 arise from a similar part of space around the head. 59 00:03:53,590 --> 00:03:55,730 OK, this is a ray-finned fish, and I'm just 60 00:03:55,730 --> 00:03:59,080 showing the retinal projections here on the right. 61 00:03:59,080 --> 00:04:03,360 This animal has a fairly simple but enlarged tectum, 62 00:04:03,360 --> 00:04:07,210 and you see a little bit of one of the accessory optic nuclei 63 00:04:07,210 --> 00:04:08,500 there. 64 00:04:08,500 --> 00:04:11,435 This huge structure down here is actually 65 00:04:11,435 --> 00:04:15,102 a backward protrusion of the hypothalamus. 66 00:04:15,102 --> 00:04:21,029 It's the inferior lobe of the hypothalamus in this fish. 67 00:04:21,029 --> 00:04:25,390 This, and animals of this group shows what that tectum is like, 68 00:04:25,390 --> 00:04:28,620 and how the axons from the retina 69 00:04:28,620 --> 00:04:31,850 come in and terminate on the superficial parts 70 00:04:31,850 --> 00:04:34,650 of the dendrites of the deep layer cells. 71 00:04:34,650 --> 00:04:38,800 There are also a few cells up in that superficial layer. 72 00:04:38,800 --> 00:04:42,085 And then this is true of mammals too, 73 00:04:42,085 --> 00:04:45,355 where the retinal input, and input from visual cortex 74 00:04:45,355 --> 00:04:48,240 come in superficially, and then in the layers 75 00:04:48,240 --> 00:04:52,690 below, in this fish it's mainly somatosensory. 76 00:04:52,690 --> 00:04:56,070 In mammals it's auditory, below the visual, 77 00:04:56,070 --> 00:04:59,540 and then in the deepest layers somatosensory. 78 00:04:59,540 --> 00:05:03,540 Remember, the spinotectal pathway. 79 00:05:03,540 --> 00:05:05,155 Coming from spinal cord. 80 00:05:05,155 --> 00:05:07,750 This is meta sensory input, especially 81 00:05:07,750 --> 00:05:16,306 from the face, which is-- it's a trigeminal tectal pathway. 82 00:05:16,306 --> 00:05:21,370 But it joins those spinotectal inputs. 83 00:05:21,370 --> 00:05:24,170 OK, here's a teleost fish, and if you just 84 00:05:24,170 --> 00:05:26,080 look at the low power over here, you'll 85 00:05:26,080 --> 00:05:30,595 see this huge tectum, the largest single structure there. 86 00:05:33,120 --> 00:05:37,840 Here's that huge lobe of the hypothalamus. 87 00:05:37,840 --> 00:05:40,430 This is cerebellum here. 88 00:05:40,430 --> 00:05:43,270 You can see the tectum's larger than the whole telencephalon. 89 00:05:46,410 --> 00:05:52,260 OK, and here is a teleost tectum done in a series of studies 90 00:05:52,260 --> 00:05:54,570 by Vanegas and his collaborators, 91 00:05:54,570 --> 00:05:59,400 where they-- this is a composite from a number 92 00:05:59,400 --> 00:06:03,900 of different studies on the cell types in the tectum. 93 00:06:03,900 --> 00:06:06,850 And you can see this beautiful laminar pattern 94 00:06:06,850 --> 00:06:09,555 that you can just see in the way axons arborize, 95 00:06:09,555 --> 00:06:11,190 and the way dendrites arborize. 96 00:06:15,830 --> 00:06:20,070 That reminds me a lot of the retina, in fact. 97 00:06:20,070 --> 00:06:21,380 OK, now this is a frog. 98 00:06:24,040 --> 00:06:25,790 I don't think I put this one in the book. 99 00:06:25,790 --> 00:06:31,906 I put the iguana next to this picture. 100 00:06:31,906 --> 00:06:34,940 There was a limit to how many figures I could use, 101 00:06:34,940 --> 00:06:39,310 and I just decided to-- you see a few more in the classroom, 102 00:06:39,310 --> 00:06:42,480 but this is a frog with a Nissl stain. 103 00:06:42,480 --> 00:06:46,240 And this is from a study of [INAUDIBLE], who 104 00:06:46,240 --> 00:06:51,340 did a number of studies of the frog, especially of the tectum. 105 00:06:51,340 --> 00:06:58,270 And what I've done is because he identified the retinal fibers 106 00:06:58,270 --> 00:07:03,305 coming in in these four layers-- he used tiny little labels, 107 00:07:03,305 --> 00:07:08,170 so I blew up the figure and I colored those axons in. 108 00:07:08,170 --> 00:07:12,220 So the retinal fibers can be seen, 109 00:07:12,220 --> 00:07:15,260 terminating in these four distinct layers. 110 00:07:15,260 --> 00:07:21,550 And that corresponded very well to the findings 111 00:07:21,550 --> 00:07:25,140 here at MIT of [INAUDIBLE] and his collaborators, 112 00:07:25,140 --> 00:07:28,976 where they were recording from these axon endings. 113 00:07:28,976 --> 00:07:33,590 They were recording the activity of four different classes 114 00:07:33,590 --> 00:07:35,040 of retina ganglion cells. 115 00:07:35,040 --> 00:07:38,330 But they actually recorded in the tectum. 116 00:07:38,330 --> 00:07:40,650 And you can see that, again, a lot of the cells 117 00:07:40,650 --> 00:07:46,020 are down-- you see over here on the left results from the cell 118 00:07:46,020 --> 00:07:46,560 stain. 119 00:07:46,560 --> 00:07:48,450 Cell and fiber stains. 120 00:07:48,450 --> 00:07:51,710 You can see fewer cells in these superficial at the top seven 121 00:07:51,710 --> 00:07:55,990 layers, and then in these deeper six layers 122 00:07:55,990 --> 00:07:58,750 you have three major cell layers. 123 00:07:58,750 --> 00:08:02,550 And that's where you see these cells with axons, just 124 00:08:02,550 --> 00:08:04,600 like the pyramidal cells, really. 125 00:08:04,600 --> 00:08:08,111 Just like in the neocortex. 126 00:08:08,111 --> 00:08:10,860 The pyramidal cell dendrites. 127 00:08:10,860 --> 00:08:13,860 Cortex also go up to the pial surface, 128 00:08:13,860 --> 00:08:16,175 just like you see here. 129 00:08:16,175 --> 00:08:20,270 And the inputs are terminating mainly on those dendrites. 130 00:08:20,270 --> 00:08:25,150 This is the iguana, where the lamination 131 00:08:25,150 --> 00:08:28,830 is particularly clear. 132 00:08:28,830 --> 00:08:32,919 This is from Bill Hall down at Duke University. 133 00:08:32,919 --> 00:08:36,080 This is a hamster in the Nissl stain, 134 00:08:36,080 --> 00:08:38,240 where I've not removed the cortex. 135 00:08:38,240 --> 00:08:41,669 But you see the evidence and lamination, 136 00:08:41,669 --> 00:08:44,220 and remember this structure? 137 00:08:44,220 --> 00:08:47,070 The central gray area, and that's the aqueduct of Sylvius 138 00:08:47,070 --> 00:08:47,570 there. 139 00:08:50,510 --> 00:08:53,280 And this is also the hamster, but now we're 140 00:08:53,280 --> 00:08:55,250 looking at a myelin stain. 141 00:08:55,250 --> 00:08:57,970 When you see it compared to the cell stain, 142 00:08:57,970 --> 00:09:01,550 the myelin is even clearer, about these layers. 143 00:09:01,550 --> 00:09:04,930 You see not so many myelinated axons 144 00:09:04,930 --> 00:09:07,970 in the superficial layer, where the retinal axons are 145 00:09:07,970 --> 00:09:11,310 terminating, and also axons from visual cortex. 146 00:09:11,310 --> 00:09:14,340 And then these are-- right below it 147 00:09:14,340 --> 00:09:17,080 is a layer of longitudinal fibers. 148 00:09:17,080 --> 00:09:19,930 So we've cut across it. 149 00:09:19,930 --> 00:09:23,060 These are including all the retinal fibers 150 00:09:23,060 --> 00:09:24,640 and privates from visual cortex. 151 00:09:24,640 --> 00:09:29,097 They come in, into that layer. 152 00:09:29,097 --> 00:09:30,680 Before they get to the tectum, they're 153 00:09:30,680 --> 00:09:32,620 traveling mostly on the surface of the brain, 154 00:09:32,620 --> 00:09:34,950 not in the tectum. 155 00:09:34,950 --> 00:09:36,990 And then there's another layer of fibers 156 00:09:36,990 --> 00:09:42,760 like that that come from cortex, and from auditory 157 00:09:42,760 --> 00:09:46,210 and somatosensory inputs. 158 00:09:46,210 --> 00:09:48,755 They're these fibers. 159 00:09:48,755 --> 00:09:50,880 And then you have the layer-- it's called the layer 160 00:09:50,880 --> 00:09:54,380 transverse fibers in [INAUDIBLE], because they're 161 00:09:54,380 --> 00:09:58,210 traveling in the transverse plane. 162 00:09:58,210 --> 00:09:59,600 Two kinds of fibers there. 163 00:09:59,600 --> 00:10:02,900 Fibers of the [INAUDIBLE], of the superior colliculus, 164 00:10:02,900 --> 00:10:06,530 but fibers from big cells in these deeper layers. 165 00:10:06,530 --> 00:10:10,570 I don't know if we can-- yes, you see some of the big cells 166 00:10:10,570 --> 00:10:11,070 here. 167 00:10:13,720 --> 00:10:17,030 The axons of those cells join these transverse fibers, 168 00:10:17,030 --> 00:10:20,460 and then go down across the midline, 169 00:10:20,460 --> 00:10:24,380 become the tectospinal tract. 170 00:10:24,380 --> 00:10:26,650 You see some of those big cells here in the rat. 171 00:10:30,844 --> 00:10:34,440 That's the rat superior colliculus. 172 00:10:34,440 --> 00:10:37,940 And topography-- let's just talk again 173 00:10:37,940 --> 00:10:40,670 about the major methods for doing topography. 174 00:10:40,670 --> 00:10:43,110 This illustrates the electrophysiological methods 175 00:10:43,110 --> 00:10:45,060 where they're recording. 176 00:10:45,060 --> 00:10:48,240 In a systematic way, here's a dorsal view 177 00:10:48,240 --> 00:10:52,110 of the goldfish tectum. 178 00:10:52,110 --> 00:10:54,950 And you see how they insert the electrodes in a grid. 179 00:10:58,810 --> 00:11:01,070 Sometimes to avoid blood vessels, 180 00:11:01,070 --> 00:11:03,265 they don't get the entire tectum. 181 00:11:06,450 --> 00:11:10,390 But they could get it if they nudged those vessels aside. 182 00:11:10,390 --> 00:11:13,230 But it's dangerous, and they lose a lot of animals that way. 183 00:11:13,230 --> 00:11:16,780 But anyway, you can see as they move the electrode from one 184 00:11:16,780 --> 00:11:20,730 position to the other, the center of the receptive fields 185 00:11:20,730 --> 00:11:21,230 move. 186 00:11:21,230 --> 00:11:25,104 And so this is a map of the visual field of the fish. 187 00:11:25,104 --> 00:11:27,460 And you can see the results of it. 188 00:11:34,210 --> 00:11:36,920 They've connected the rostral caudal rows 189 00:11:36,920 --> 00:11:42,240 of penetration sites, showing the orderly topography 190 00:11:42,240 --> 00:11:43,300 of the projection. 191 00:11:43,300 --> 00:11:46,400 And then this one we talked about before. 192 00:11:46,400 --> 00:11:50,670 This is one from work of me and my students and the hamster, 193 00:11:50,670 --> 00:11:55,310 where the initial method was anatomically making lesions 194 00:11:55,310 --> 00:12:00,880 in the retina, and tracing degeneration to the tectum. 195 00:12:00,880 --> 00:12:03,520 Now it would be more likely done with injection methods. 196 00:12:03,520 --> 00:12:06,980 I've done that also, where you can 197 00:12:06,980 --> 00:12:09,835 get a more limited number of retina ganglion cells. 198 00:12:09,835 --> 00:12:11,210 When you make lesions, of course, 199 00:12:11,210 --> 00:12:14,560 you get all the axons traveling towards the optic disc 200 00:12:14,560 --> 00:12:17,250 from the more peripheral parts. 201 00:12:17,250 --> 00:12:21,290 But anyway, you can get a nice map. 202 00:12:21,290 --> 00:12:26,650 The letters there stand for the center of the eye muscles 203 00:12:26,650 --> 00:12:29,800 at the temporal pole, the nasal pole of the retina, 204 00:12:29,800 --> 00:12:32,630 superior and inferior. 205 00:12:32,630 --> 00:12:34,220 We call them the rectus muscles. 206 00:12:34,220 --> 00:12:40,420 Superior rectus, temporal rectus, and-- actually, 207 00:12:40,420 --> 00:12:44,450 for temporal retinas, we call it the lateral rectus. 208 00:12:44,450 --> 00:12:47,766 And similarly, for the nasal one we call it the medial rectus. 209 00:12:50,520 --> 00:12:55,470 But they're easily repeated landmarks from one animal 210 00:12:55,470 --> 00:12:59,670 to the other, so we get consistent results. 211 00:12:59,670 --> 00:13:05,140 And then we take-- this is the view of the embryonic hamster 212 00:13:05,140 --> 00:13:08,090 up here, and this is that flattened view. 213 00:13:08,090 --> 00:13:10,260 And we take the flattened view here, 214 00:13:10,260 --> 00:13:14,250 we can show the topography-- I show 215 00:13:14,250 --> 00:13:19,360 the superior, inferior retinal axis just once out of here, 216 00:13:19,360 --> 00:13:23,975 because the axons assume that topography very early. 217 00:13:23,975 --> 00:13:26,650 When you get not very far beyond the chiasm. 218 00:13:26,650 --> 00:13:29,960 By the time they get to the geniculate bodies, 219 00:13:29,960 --> 00:13:35,615 you have the inferior retina fibers all at one edge, 220 00:13:35,615 --> 00:13:37,910 and the superior retina fibers all at the other edge. 221 00:13:44,350 --> 00:13:46,340 Of course, you have to know which 222 00:13:46,340 --> 00:13:49,220 is-- this would be the rostral edge, 223 00:13:49,220 --> 00:13:52,510 and then it medial edge at the optic tract here. 224 00:13:52,510 --> 00:13:59,310 And this would be the caudal edge, 225 00:13:59,310 --> 00:14:02,820 which becomes the lateral edge in the optic tract here. 226 00:14:02,820 --> 00:14:06,560 And then I'm showing how the nasal temporal-- actually, 227 00:14:06,560 --> 00:14:09,090 those axons are all mixed together 228 00:14:09,090 --> 00:14:11,460 when they're in the tract here. 229 00:14:11,460 --> 00:14:13,600 And they stay mixed together, even when 230 00:14:13,600 --> 00:14:16,090 they're reaching the geniculate bodies. 231 00:14:16,090 --> 00:14:19,780 But then they're forming and following 232 00:14:19,780 --> 00:14:25,480 the chemical cues that determine where they branch and enter 233 00:14:25,480 --> 00:14:30,620 the nucleus, what you see here. 234 00:14:30,620 --> 00:14:35,380 And here I've added the topographies. 235 00:14:35,380 --> 00:14:40,480 So you'll notice here that in the geniculate bodies 236 00:14:40,480 --> 00:14:43,710 and in the pretectum you get the same kind of topography. 237 00:14:43,710 --> 00:14:49,010 Nasal first, then temporal retina, and then it switches. 238 00:14:49,010 --> 00:14:51,430 Nasal again, and temporal. 239 00:14:51,430 --> 00:14:53,566 pretectum doesn't have very precise topography, 240 00:14:53,566 --> 00:14:56,680 but there still is a pretendency for the nasal retina 241 00:14:56,680 --> 00:14:59,850 to terminate first here, and then the temporal retina. 242 00:14:59,850 --> 00:15:01,675 Then in the tectum, it switches. 243 00:15:01,675 --> 00:15:06,940 You get the Temporal retina first, and then the nasal. 244 00:15:06,940 --> 00:15:10,660 So these terminal areas are strung out 245 00:15:10,660 --> 00:15:12,865 along the optic tract like a string of beads. 246 00:15:12,865 --> 00:15:16,430 A very orderly arrangement of axons, 247 00:15:16,430 --> 00:15:17,680 and orderly terminations. 248 00:15:21,620 --> 00:15:25,160 So in the dorsal geniculate, as you would expect here 249 00:15:25,160 --> 00:15:29,740 in the temporal part, temporal retina part representing 250 00:15:29,740 --> 00:15:32,490 the field right in front of the nasal field, 251 00:15:32,490 --> 00:15:38,440 that's where you get the bilateral projections. 252 00:15:38,440 --> 00:15:41,570 Projections from the two eyes in separate layers. 253 00:15:48,390 --> 00:15:52,900 Just the beginning here, today I really want 254 00:15:52,900 --> 00:16:00,360 to talk mainly about the multiple routes, 255 00:16:00,360 --> 00:16:04,240 major transcortical fibers. 256 00:16:04,240 --> 00:16:04,740 OK. 257 00:16:07,780 --> 00:16:10,185 Make sure you can relate these kinds of pictures. 258 00:16:10,185 --> 00:16:12,990 We were looking at a real brain from the side, 259 00:16:12,990 --> 00:16:15,970 and we were looking at this stretched out view. 260 00:16:19,630 --> 00:16:23,740 First of all, let's see what the accessory optic tract is. 261 00:16:23,740 --> 00:16:25,540 In this kind of picture, it's these axons 262 00:16:25,540 --> 00:16:30,170 that leave the main tract, and in many small animals 263 00:16:30,170 --> 00:16:32,836 they leave them in three different place. 264 00:16:32,836 --> 00:16:36,090 And if you look at a reconstruction, 265 00:16:36,090 --> 00:16:38,889 they're leaving up here, they're leaving here, 266 00:16:38,889 --> 00:16:39,930 and they're leaving here. 267 00:16:39,930 --> 00:16:41,721 So I can show you where they're terminating 268 00:16:41,721 --> 00:16:49,750 the accessory optic tract nuclei, there, there, and here. 269 00:16:49,750 --> 00:16:54,530 This nucleus is mostly behind the peduncle and the nigra. 270 00:16:54,530 --> 00:16:55,760 OK? 271 00:16:55,760 --> 00:17:00,410 But I'm drawing this as if the brain were transparent. 272 00:17:00,410 --> 00:17:03,415 So this is the medial terminal nucleus, the lateral terminal 273 00:17:03,415 --> 00:17:05,540 nucleus, and the dorsal terminal nucleus. 274 00:17:05,540 --> 00:17:07,849 And the axons that get to the lateral 275 00:17:07,849 --> 00:17:12,380 are going like that and like that. 276 00:17:12,380 --> 00:17:17,214 Here we have what we call the inferior fasciculus, which 277 00:17:17,214 --> 00:17:22,060 is traveling along the lateral edge of the hypothalamus. 278 00:17:22,060 --> 00:17:27,740 And then here you have axons going in both directions 279 00:17:27,740 --> 00:17:34,040 to reach those two terminal nuclei. 280 00:17:34,040 --> 00:17:37,740 The dorsal one is really-- it's just 281 00:17:37,740 --> 00:17:41,230 like a little addition to the nucleus of the optic tract, 282 00:17:41,230 --> 00:17:45,680 which could be considered part of the accessory optic system 283 00:17:45,680 --> 00:17:48,695 in the way its cells respond. 284 00:17:48,695 --> 00:17:49,695 So what is the function? 285 00:17:49,695 --> 00:17:50,805 Do you remember? 286 00:17:50,805 --> 00:17:53,730 I mentioned it a few times. 287 00:17:53,730 --> 00:17:57,010 Discovered by one of our former students. 288 00:17:57,010 --> 00:17:58,560 You ever heard me talk about it? 289 00:17:58,560 --> 00:18:00,985 He decided he was going to solve the problem. 290 00:18:00,985 --> 00:18:02,520 His name was Simpson. 291 00:18:02,520 --> 00:18:08,320 He recorded from these groups of neurons, 292 00:18:08,320 --> 00:18:11,630 and found that they always responded 293 00:18:11,630 --> 00:18:15,330 to movement of the whole visual field across the retina. 294 00:18:15,330 --> 00:18:17,979 So not small objects. 295 00:18:17,979 --> 00:18:19,270 Everything moved in the retina. 296 00:18:19,270 --> 00:18:20,790 It's the kind of thing that happens 297 00:18:20,790 --> 00:18:24,760 when you turn your head, when you're locomoting, 298 00:18:24,760 --> 00:18:28,250 or when you're tipping over. 299 00:18:28,250 --> 00:18:31,550 So it's a vestibular-like function that they're serving. 300 00:18:31,550 --> 00:18:34,278 Signaling head movement and head position. 301 00:18:39,160 --> 00:18:40,120 OK. 302 00:18:40,120 --> 00:18:46,599 Now, the multiple routes from the retina to the endbrain. 303 00:18:46,599 --> 00:18:49,920 And we'll discuss the optic radiations, 304 00:18:49,920 --> 00:18:55,810 which refers to the major routes from the thalamus 305 00:18:55,810 --> 00:19:00,110 to the visual areas of the cortex. 306 00:19:00,110 --> 00:19:06,710 Usually textbooks only mention two of these. 307 00:19:06,710 --> 00:19:10,810 But I had to mention more. 308 00:19:10,810 --> 00:19:12,660 For one thing, I'm dealing with evolution, 309 00:19:12,660 --> 00:19:16,769 and I want you to understand there's a lot more 310 00:19:16,769 --> 00:19:18,185 to evolution and the visual system 311 00:19:18,185 --> 00:19:21,620 than just those two pathways. 312 00:19:21,620 --> 00:19:25,490 And secondly, because at least one more of those, 313 00:19:25,490 --> 00:19:31,140 and maybe more than one are still very important. 314 00:19:31,140 --> 00:19:33,100 Just because it's neglected by neuroscientists 315 00:19:33,100 --> 00:19:34,433 doesn't mean it's not important. 316 00:19:34,433 --> 00:19:38,070 It just means they don't study it as much. 317 00:19:38,070 --> 00:19:39,520 OK. 318 00:19:39,520 --> 00:19:42,850 First of all, let's bring up this rule about evolution. 319 00:19:42,850 --> 00:19:44,780 What is Deacon's rule? 320 00:19:44,780 --> 00:19:46,880 We summarize it by saying it means 321 00:19:46,880 --> 00:19:50,600 large equals well connected. 322 00:19:50,600 --> 00:19:53,030 It's an important rule of thumb in brain [? imaging. ?] 323 00:19:53,030 --> 00:19:55,870 So what does it suggest about the multiple routes 324 00:19:55,870 --> 00:19:57,735 to the forebrain for visual information? 325 00:20:01,200 --> 00:20:08,005 What is the large structure that gets retinal input? 326 00:20:08,005 --> 00:20:10,370 Of all those structures along the optic tract, 327 00:20:10,370 --> 00:20:11,450 what's the biggest one? 328 00:20:15,640 --> 00:20:18,740 Probably superior colliculus in most animals. 329 00:20:18,740 --> 00:20:20,225 Remember, we started with the fish 330 00:20:20,225 --> 00:20:24,840 and saw its optic tectum is bigger than the whole endbrain. 331 00:20:24,840 --> 00:20:27,110 I showed you a photograph talking 332 00:20:27,110 --> 00:20:32,580 about midbrain of a barracuda-- a predator fish. 333 00:20:32,580 --> 00:20:38,791 The tectum is so huge it dwarfs the rest of the brain. 334 00:20:38,791 --> 00:20:43,435 And all the predatory fish that are very visual predatory fish 335 00:20:43,435 --> 00:20:44,546 are like that. 336 00:20:47,430 --> 00:20:51,400 Some of them, like sharks, use olfaction quite a bit as well. 337 00:20:51,400 --> 00:20:53,820 And they also use other senses. 338 00:20:56,540 --> 00:21:00,290 But many predatory fish depend mainly on vision. 339 00:21:00,290 --> 00:21:03,470 OK, so it suggests-- if it's better 340 00:21:03,470 --> 00:21:06,005 connected than the others, it suggests 341 00:21:06,005 --> 00:21:09,735 that we should look at tectum for the source of axons 342 00:21:09,735 --> 00:21:12,710 that reach the endbrain. 343 00:21:12,710 --> 00:21:16,970 Well, it turns out the midbrain didn't connect directly 344 00:21:16,970 --> 00:21:21,500 to the endbrain. 345 00:21:21,500 --> 00:21:24,770 OK, there might be a few exceptions, but not many. 346 00:21:24,770 --> 00:21:29,600 We know that those axons that determine brain state, 347 00:21:29,600 --> 00:21:33,510 like the norepinephrine axons and the serotonin axons, 348 00:21:33,510 --> 00:21:36,215 they come from midbrain and hindbrain, 349 00:21:36,215 --> 00:21:38,940 and they certainly project into the endbrain. 350 00:21:38,940 --> 00:21:43,306 But they're not the ones carrying specific information. 351 00:21:43,306 --> 00:21:46,930 They determine the state of the whole brain. 352 00:21:46,930 --> 00:21:54,310 OK, so, what are the two routes to the endbrain 353 00:21:54,310 --> 00:21:56,570 taken by visual information that are usually 354 00:21:56,570 --> 00:21:59,000 considered the major ones? 355 00:21:59,000 --> 00:22:03,040 By now you should be getting that figured out. 356 00:22:03,040 --> 00:22:06,010 What do we talk about all the time? 357 00:22:06,010 --> 00:22:09,680 If someone just talks about-- he's giving 358 00:22:09,680 --> 00:22:11,540 a talk in our department, and say, 359 00:22:11,540 --> 00:22:13,430 giving a talk about the visual system, 360 00:22:13,430 --> 00:22:16,660 what does it usually mean? 361 00:22:16,660 --> 00:22:18,980 Geniculostriate system. 362 00:22:18,980 --> 00:22:22,916 Because it's become so dominant in the primates. 363 00:22:22,916 --> 00:22:27,330 OK, but what's the other big one? 364 00:22:27,330 --> 00:22:31,110 It became very clear from the studies of birds 365 00:22:31,110 --> 00:22:35,270 that birds have something like a geniculostriate system, 366 00:22:35,270 --> 00:22:38,390 but in fact they have a bigger pathway 367 00:22:38,390 --> 00:22:41,090 common from-- remember Deacon's rule-- 368 00:22:41,090 --> 00:22:43,080 it comes from the tectum. 369 00:22:43,080 --> 00:22:46,420 From this tectum to thalamus, to a nucleus that in the bird 370 00:22:46,420 --> 00:22:48,780 is called nucleus rotundus. 371 00:22:48,780 --> 00:22:54,540 That projects to the endbrain to part 372 00:22:54,540 --> 00:22:56,105 of the so-called [INAUDIBLE]. 373 00:22:56,105 --> 00:22:59,720 I'll show you that. 374 00:22:59,720 --> 00:23:06,470 In mammals, in the book I list six routes, here it's seven. 375 00:23:06,470 --> 00:23:08,470 They're actually all in the book, too, 376 00:23:08,470 --> 00:23:13,720 but I had discussed number six here, 377 00:23:13,720 --> 00:23:15,690 though I'm going to the amygdala, which 378 00:23:15,690 --> 00:23:18,250 isn't as well known as the auditory pathway 379 00:23:18,250 --> 00:23:20,010 to the amygdala. 380 00:23:20,010 --> 00:23:27,070 And I mentioned it in the first visual chapter, chapter 20. 381 00:23:27,070 --> 00:23:31,200 And I don't know why I didn't get it back into this list. 382 00:23:31,200 --> 00:23:34,472 Probably because I had written this chapter already. 383 00:23:34,472 --> 00:23:38,670 I didn't always write this in order. 384 00:23:38,670 --> 00:23:41,140 But this is the way it probably should be, 385 00:23:41,140 --> 00:23:42,950 with seven major pathways. 386 00:23:42,950 --> 00:23:46,220 The visual information to take to the endbrain-- these 387 00:23:46,220 --> 00:23:48,440 are the two biggest in most animals. 388 00:23:51,015 --> 00:23:52,356 OK? 389 00:23:52,356 --> 00:23:55,510 But there's the route from the subthalamus. 390 00:23:55,510 --> 00:23:58,240 Recently they've even found routes from the subthalamus 391 00:23:58,240 --> 00:24:01,850 directly to cortex, but we don't know 392 00:24:01,850 --> 00:24:03,520 how many species it occurs in. 393 00:24:03,520 --> 00:24:05,184 It goes to the barrel fields. 394 00:24:08,220 --> 00:24:11,110 I think more important for most animals is 395 00:24:11,110 --> 00:24:13,830 that that area in the zona incerta here, 396 00:24:13,830 --> 00:24:17,470 does get visual input from the ventrolateral geniculate body, 397 00:24:17,470 --> 00:24:20,740 and it doesn't just project to the locomotor area. 398 00:24:20,740 --> 00:24:21,680 The midbrain. 399 00:24:21,680 --> 00:24:25,070 You can control escape behavior that way. 400 00:24:25,070 --> 00:24:27,760 It also projects to the dorsal thalamus, 401 00:24:27,760 --> 00:24:29,770 the midline and ventrolateral nuclei, 402 00:24:29,770 --> 00:24:32,150 which affect the whole thalamus, certainly 403 00:24:32,150 --> 00:24:34,200 sending visual information to the endbrain, 404 00:24:34,200 --> 00:24:37,580 to the cortex, and the striatum. 405 00:24:37,580 --> 00:24:40,730 Those structures project to both striatum and cortex. 406 00:24:40,730 --> 00:24:43,160 And then optic tectum and pretectum 407 00:24:43,160 --> 00:24:45,470 have deeper layers that are multi-modal, 408 00:24:45,470 --> 00:24:47,850 but it includes visual information. 409 00:24:47,850 --> 00:24:50,910 They project into the lateral thalamus, and then 410 00:24:50,910 --> 00:24:58,120 the superficial visual layers, including optic tectum 411 00:24:58,120 --> 00:25:01,270 and pretectum, they both have pathways carrying 412 00:25:01,270 --> 00:25:06,250 specific visual information into the thalamus. 413 00:25:06,250 --> 00:25:09,480 Some of it does go to the lateral geniculate part. 414 00:25:09,480 --> 00:25:12,784 In fact, most of it goes into the lateral thalamus 415 00:25:12,784 --> 00:25:13,617 near the geniculate. 416 00:25:13,617 --> 00:25:15,822 Goes to LP. 417 00:25:15,822 --> 00:25:19,840 In primates, it's usually called pulvinar. 418 00:25:19,840 --> 00:25:23,620 And that goes to posterior neocortex. 419 00:25:23,620 --> 00:25:27,880 Not primarily striate cortex. 420 00:25:27,880 --> 00:25:30,350 And we're going to encounter this one from the pretectum 421 00:25:30,350 --> 00:25:32,695 again, because it's signaling changes 422 00:25:32,695 --> 00:25:34,270 in head direction, which turn out 423 00:25:34,270 --> 00:25:38,910 to be really important in where we are, and where we're going. 424 00:25:38,910 --> 00:25:41,580 OK. 425 00:25:41,580 --> 00:25:43,585 So I pointed out here that that first pathway 426 00:25:43,585 --> 00:25:46,866 is almost always-- usually ignored, 427 00:25:46,866 --> 00:25:50,960 in spite of its possible importance in evolution 428 00:25:50,960 --> 00:25:52,945 especially. 429 00:25:52,945 --> 00:25:55,390 The second, third, and fourth have 430 00:25:55,390 --> 00:25:59,490 attracted a few researchers, but they're usually not mentioned. 431 00:25:59,490 --> 00:26:01,620 Two, three, and four. 432 00:26:01,620 --> 00:26:05,000 It's this one that I think is going 433 00:26:05,000 --> 00:26:08,730 to attract a lot more attention in the future. 434 00:26:08,730 --> 00:26:14,140 I've made it a major topic in the book 435 00:26:14,140 --> 00:26:17,570 when we talk about hippocampus. 436 00:26:17,570 --> 00:26:19,540 And the one to the amygdala, it's 437 00:26:19,540 --> 00:26:22,197 the auditory system that's dominated that study, 438 00:26:22,197 --> 00:26:24,530 but it turns out that it's a visual pathway going there, 439 00:26:24,530 --> 00:26:25,115 too. 440 00:26:25,115 --> 00:26:27,240 It might be very important in effective emotions. 441 00:26:29,770 --> 00:26:35,240 But the optic tectum and the LGB are the main ones. 442 00:26:35,240 --> 00:26:38,380 I just talk a little bit here-- this is somewhat speculative. 443 00:26:38,380 --> 00:26:42,910 It's about how this organization between pathways 444 00:26:42,910 --> 00:26:46,740 from midbrain into thalamus form. 445 00:26:46,740 --> 00:26:48,540 But this is the one I want to stress here 446 00:26:48,540 --> 00:26:51,480 in the class, that shows those two major pathways. 447 00:26:51,480 --> 00:26:57,090 I used the same color code for mammals, reptiles, and birds. 448 00:26:57,090 --> 00:27:00,860 In the mammal we call them lateral geniculate, and LP, 449 00:27:00,860 --> 00:27:01,810 or pulvinar. 450 00:27:01,810 --> 00:27:04,470 Lateral posterior nucleus or pulvinar. 451 00:27:04,470 --> 00:27:10,155 And it shows that the geniculate body goes to striate, LP 452 00:27:10,155 --> 00:27:14,020 pulvinar primarily to exostriate. 453 00:27:14,020 --> 00:27:15,960 I say primarily because it does have 454 00:27:15,960 --> 00:27:17,200 more widespread projections. 455 00:27:17,200 --> 00:27:19,800 At least some of its neurons do as well. 456 00:27:22,560 --> 00:27:26,330 In reptiles they get different names, 457 00:27:26,330 --> 00:27:29,930 but you still have separate projections. 458 00:27:29,930 --> 00:27:33,180 In relative terms, the one that gets direct retina 459 00:27:33,180 --> 00:27:40,920 input, dorsolateral optic nucleus, this optic nucleus 460 00:27:40,920 --> 00:27:45,970 in the thalamus of the bird, they project directly to walls 461 00:27:45,970 --> 00:27:48,105 through dorsolateral cortex. 462 00:27:48,105 --> 00:27:50,950 It's part of the dorsal cortex in the reptile. 463 00:27:50,950 --> 00:27:54,800 It's just given a different name in the bird. 464 00:27:54,800 --> 00:27:56,370 Wilson's bulge. 465 00:27:56,370 --> 00:27:59,500 And because it does in some birds, where 466 00:27:59,500 --> 00:28:01,942 it's well developed, like the owl, 467 00:28:01,942 --> 00:28:05,190 it does form a prominent bulge in the endbrain. 468 00:28:07,890 --> 00:28:10,190 Part of it gets directed through visual input. 469 00:28:10,190 --> 00:28:12,700 There's a somatosensory [? wolst ?] as well, 470 00:28:12,700 --> 00:28:15,730 and a motor [? wolst. ?] 471 00:28:15,730 --> 00:28:19,780 And the other one in these reptiles and birds 472 00:28:19,780 --> 00:28:23,700 goes subcortically to this dorsal ventricular ridge 473 00:28:23,700 --> 00:28:27,260 here, that has been found in its connections 474 00:28:27,260 --> 00:28:29,478 to be like neocortex in mammals. 475 00:28:29,478 --> 00:28:31,870 OK? 476 00:28:31,870 --> 00:28:34,150 But in terms of connections, they 477 00:28:34,150 --> 00:28:38,220 have these same pathways, same kinds of connections. 478 00:28:38,220 --> 00:28:40,660 Difference is just the arrangement of the cells 479 00:28:40,660 --> 00:28:41,620 where they terminate. 480 00:28:45,110 --> 00:28:46,530 All right. 481 00:28:46,530 --> 00:28:50,730 This just is-- I took a picture of a turtle 482 00:28:50,730 --> 00:28:53,960 where I found nice studies of these different projections. 483 00:28:53,960 --> 00:28:57,470 And here I've shown where the visual projections are going. 484 00:28:57,470 --> 00:29:00,910 In the dorsal ventricular ridge of the turtle. 485 00:29:03,800 --> 00:29:08,574 And you can see the cells form a nice, distinct pattern there. 486 00:29:11,480 --> 00:29:16,586 And this is where the more direct projection goes, 487 00:29:16,586 --> 00:29:18,010 from the rotundus of the turtle. 488 00:29:22,960 --> 00:29:25,540 Most of the are concentrated on this area, 489 00:29:25,540 --> 00:29:29,955 but my readings are very clear that it goes also 490 00:29:29,955 --> 00:29:33,400 to this thickened area out here. 491 00:29:36,850 --> 00:29:40,400 All right, so those are the two pathways, 492 00:29:40,400 --> 00:29:43,810 shown in a little more detail for the turtle. 493 00:29:43,810 --> 00:29:47,405 And here is a raccoon's striate cortex. 494 00:29:47,405 --> 00:29:49,430 I didn't put this one in the book. 495 00:29:49,430 --> 00:29:51,040 I put the monkey. 496 00:29:51,040 --> 00:29:54,760 But you see, even in a very low power here, 497 00:29:54,760 --> 00:29:57,392 look how the striate cortex stands out. 498 00:29:57,392 --> 00:30:05,130 You see that very dense layer of granule cells 499 00:30:05,130 --> 00:30:08,280 next to a layer of fibers that looks wider. 500 00:30:08,280 --> 00:30:15,900 And this is the calcarine fissure in the raccoon. 501 00:30:15,900 --> 00:30:19,760 But you can very clearly see the striate cortex, 502 00:30:19,760 --> 00:30:21,505 and then you see the sudden change when 503 00:30:21,505 --> 00:30:23,085 you get to the border of striate, 504 00:30:23,085 --> 00:30:25,702 and the extra striate areas. 505 00:30:25,702 --> 00:30:26,630 OK? 506 00:30:26,630 --> 00:30:30,240 This is the one I took out of the book. 507 00:30:30,240 --> 00:30:37,200 It comes from [INAUDIBLE] picture, 508 00:30:37,200 --> 00:30:40,352 where again, it's even clearer at this magnification 509 00:30:40,352 --> 00:30:41,820 for the monkey. 510 00:30:41,820 --> 00:30:45,000 You see the striate cortex. 511 00:30:45,000 --> 00:30:47,800 Very clear lamination. 512 00:30:47,800 --> 00:30:49,810 And you see the sudden change. 513 00:30:49,810 --> 00:30:53,950 He's labeled that border D here, between striate area 514 00:30:53,950 --> 00:30:54,966 and exostriate. 515 00:30:54,966 --> 00:30:59,370 You see the sudden change in the cyto architecture. 516 00:30:59,370 --> 00:31:00,750 Very easy to pick up. 517 00:31:00,750 --> 00:31:04,580 So if I showed you this picture and didn't label it for you, 518 00:31:04,580 --> 00:31:07,890 you should be able to label that boundary. 519 00:31:07,890 --> 00:31:12,580 At least there and here. 520 00:31:12,580 --> 00:31:13,125 And here. 521 00:31:23,520 --> 00:31:26,760 So what are the visual areas of the neocortex that are the most 522 00:31:26,760 --> 00:31:28,820 primitive that we keep seeing? 523 00:31:31,637 --> 00:31:33,470 We're talking about neocortex, so we're only 524 00:31:33,470 --> 00:31:34,790 talking about mammals. 525 00:31:34,790 --> 00:31:36,110 OK? 526 00:31:36,110 --> 00:31:41,105 So if we look at all the mammals that 527 00:31:41,105 --> 00:31:44,790 have been studied, including some very primitive ones, 528 00:31:44,790 --> 00:31:48,466 you keep seeing primary visual cortex. 529 00:31:51,532 --> 00:31:53,490 What does that mean about those other pathways? 530 00:31:53,490 --> 00:31:57,460 Well, we see those in non-mammals as well. 531 00:31:57,460 --> 00:31:59,590 OK? 532 00:31:59,590 --> 00:32:02,515 And they were no doubt there in the cynodonts 533 00:32:02,515 --> 00:32:04,490 that led to mammals. 534 00:32:04,490 --> 00:32:05,940 The evolution of mammals. 535 00:32:09,170 --> 00:32:12,600 So for mammals, you can say the striate cortex 536 00:32:12,600 --> 00:32:15,080 and the immediately adjacent area, 537 00:32:15,080 --> 00:32:21,800 what we call V2 if we're physiologists, 538 00:32:21,800 --> 00:32:24,366 consists, actually, of a number of different representations 539 00:32:24,366 --> 00:32:26,705 of the visual field, as we will see. 540 00:32:30,340 --> 00:32:33,293 They've been called V2, V3, V4, and so forth 541 00:32:33,293 --> 00:32:37,280 by the physiologists that have divided it up 542 00:32:37,280 --> 00:32:41,243 according to representations of the visual field. 543 00:32:41,243 --> 00:32:42,600 OK. 544 00:32:42,600 --> 00:32:45,720 And then what do we mean by temporalization 545 00:32:45,720 --> 00:32:48,761 of the cerebral hemispheres? 546 00:32:48,761 --> 00:32:51,440 In development and evolution, it's 547 00:32:51,440 --> 00:32:55,450 correlated with the expansion of one group of thalamic nuclei. 548 00:32:55,450 --> 00:32:59,300 Which ones am I talking about? 549 00:32:59,300 --> 00:33:04,445 Temporalization, formation of a prominent temporal lobe. 550 00:33:04,445 --> 00:33:06,670 That's what temporalization is. 551 00:33:06,670 --> 00:33:11,085 What's happening to cause that? 552 00:33:11,085 --> 00:33:17,750 It's an expansion of the uni-modal and multi-modal 553 00:33:17,750 --> 00:33:21,910 association areas of posterior cortex. 554 00:33:21,910 --> 00:33:24,396 Primarily visual. 555 00:33:24,396 --> 00:33:28,675 It expands so much, you know? 556 00:33:34,580 --> 00:33:37,190 Sorry? 557 00:33:37,190 --> 00:33:41,950 Oh, it's associated with the lateral thalamite nucleus, 558 00:33:41,950 --> 00:33:45,520 and in primates it's mostly pulvinar. 559 00:33:45,520 --> 00:33:48,140 See, here I show an animal like a rodent, 560 00:33:48,140 --> 00:33:50,346 that doesn't have a temporal lobe. 561 00:33:50,346 --> 00:33:51,720 And then I'm showing what happens 562 00:33:51,720 --> 00:33:56,510 if the posterior areas, concerned 563 00:33:56,510 --> 00:33:58,475 with vision and audition, expand. 564 00:34:03,217 --> 00:34:05,050 I mean, there's not room in the skull for it 565 00:34:05,050 --> 00:34:07,045 just to expand, and expand, and expand. 566 00:34:07,045 --> 00:34:16,330 So it forms a whole lobe that folds in, like a grub here, 567 00:34:16,330 --> 00:34:19,350 and with it comes the hippocampus. 568 00:34:19,350 --> 00:34:21,600 I'm showing how the position of the hippocampus 569 00:34:21,600 --> 00:34:23,780 changes in relative position. 570 00:34:23,780 --> 00:34:30,139 But the topography, the topology is the same. 571 00:34:30,139 --> 00:34:36,190 This is all visual areas, from about here all the way 572 00:34:36,190 --> 00:34:40,600 down to here in the primate. 573 00:34:40,600 --> 00:34:42,492 And there's hippocampus nearby. 574 00:34:45,054 --> 00:34:45,970 So that's the process. 575 00:34:50,188 --> 00:34:52,759 Well, let's look at in the optic radiations, which 576 00:34:52,759 --> 00:34:54,789 are the fibers coming from thalamus, 577 00:34:54,789 --> 00:34:56,870 you know, up to that visual cortex. 578 00:35:00,020 --> 00:35:03,650 We saw it in this picture that-- I 579 00:35:03,650 --> 00:35:08,520 think I had very early on from [? plexus ?] work, 580 00:35:08,520 --> 00:35:11,963 German anatomist that published a developmental study 581 00:35:11,963 --> 00:35:13,180 of myelinization. 582 00:35:13,180 --> 00:35:18,710 This is from a seven week human, where myelin is just 583 00:35:18,710 --> 00:35:20,480 beginning to appear to in the hemispheres. 584 00:35:20,480 --> 00:35:22,815 And he shows it's appearing first 585 00:35:22,815 --> 00:35:25,670 in this pathway to the occipital lobe. 586 00:35:25,670 --> 00:35:28,500 That's the genicular striate pathway. 587 00:35:28,500 --> 00:35:33,875 It also appears in the primary auditory radiations, 588 00:35:33,875 --> 00:35:38,192 the auditory context, and it appears-- 589 00:35:38,192 --> 00:35:41,866 it's actually earliest here through the somatosensory 590 00:35:41,866 --> 00:35:46,940 cortex, in the ventral posterior thalamus. 591 00:35:46,940 --> 00:35:49,070 So there's a lot of myelin in the cerebellum. 592 00:35:49,070 --> 00:35:51,420 There's a lot of myelin in the hindbrain 593 00:35:51,420 --> 00:35:56,790 and other parts of the brain stem. 594 00:35:56,790 --> 00:36:01,542 But just starting in the hemispheres. 595 00:36:01,542 --> 00:36:05,611 And it appears first there in the geniculate striate pathway. 596 00:36:08,700 --> 00:36:12,700 This just shows you what I did to make this picture. 597 00:36:12,700 --> 00:36:15,170 I had the original plexic picture, 598 00:36:15,170 --> 00:36:17,800 which I got from the University of Chicago. 599 00:36:17,800 --> 00:36:22,988 And these were German labels that he had in there. 600 00:36:22,988 --> 00:36:29,160 So I carefully removed them, and the artist 601 00:36:29,160 --> 00:36:32,810 helped in removing the lines here, and everything. 602 00:36:32,810 --> 00:36:36,410 And I put in the major labels we needed 603 00:36:36,410 --> 00:36:38,370 to understand that picture. 604 00:36:38,370 --> 00:36:40,390 OK, and these are some very nice pictures 605 00:36:40,390 --> 00:36:42,250 of the growth of the human brain that you 606 00:36:42,250 --> 00:36:46,270 can see the change in relative size. 607 00:36:46,270 --> 00:36:55,336 These are all to the same scale from that-- 10 weeks, 608 00:36:55,336 --> 00:36:58,130 up to 41 weeks gestation. 609 00:36:58,130 --> 00:37:07,400 So this is it for-- birth is 40 or 41 weeks in that. 610 00:37:07,400 --> 00:37:10,880 So back here you have a brain that's 611 00:37:10,880 --> 00:37:12,585 about at the stage of development 612 00:37:12,585 --> 00:37:14,935 of a hamster at birth. 613 00:37:14,935 --> 00:37:19,200 Because a hamster's born and the stage that 614 00:37:19,200 --> 00:37:24,060 corresponds to a premature human. 615 00:37:24,060 --> 00:37:26,670 A prenatal human. 616 00:37:26,670 --> 00:37:30,480 About a 2 and 1/2 month human. 617 00:37:30,480 --> 00:37:33,930 All right, and there you see the temporal lobe forming. 618 00:37:33,930 --> 00:37:36,060 See, it starts really early. 619 00:37:36,060 --> 00:37:38,150 Humans have a very large temporal lobe. 620 00:37:38,150 --> 00:37:40,866 Already at 12 weeks it's beginning, 621 00:37:40,866 --> 00:37:44,085 and then you see the progressive expansion of it. 622 00:37:44,085 --> 00:37:47,730 The visual areas end up being just visible only 623 00:37:47,730 --> 00:37:49,425 at the pole there in humans. 624 00:37:49,425 --> 00:37:52,230 And if you look at the medial view, 625 00:37:52,230 --> 00:37:56,692 very early you see the calcarine fissure folding in. 626 00:37:56,692 --> 00:38:01,580 So this is all visual cortex here. 627 00:38:01,580 --> 00:38:04,248 In the adult it's all along the deep fissure. 628 00:38:07,390 --> 00:38:13,180 This just shows you the temporal lobe at the temporal area 629 00:38:13,180 --> 00:38:15,980 of an animal that doesn't have a temporal lobe, 630 00:38:15,980 --> 00:38:18,780 but he's still got an auditory cortex here. 631 00:38:18,780 --> 00:38:25,200 And small areas outside the striate area, which is here, 632 00:38:25,200 --> 00:38:29,610 that do correspond to some of those areas 633 00:38:29,610 --> 00:38:31,940 outside the striate cortex in a human. 634 00:38:31,940 --> 00:38:35,450 But of course, in monkeys. 635 00:38:35,450 --> 00:38:39,560 A lot of them are simply not there in the rodent. 636 00:38:39,560 --> 00:38:44,670 And then it's happening very differently in the cat. 637 00:38:44,670 --> 00:38:49,000 Now, we call this the pseudo Sylvian fissure, 638 00:38:49,000 --> 00:38:52,315 because it goes up right in the middle of auditory areas. 639 00:38:52,315 --> 00:38:56,320 Whereas in the primates, the monkey and the human, 640 00:38:56,320 --> 00:39:01,620 the auditory areas are always below that deep fissure. 641 00:39:04,180 --> 00:39:08,546 OK, so there's the temporalization picture. 642 00:39:08,546 --> 00:39:10,046 Once you understand temporalization, 643 00:39:10,046 --> 00:39:15,168 you can understand what Meyer's loop is. 644 00:39:15,168 --> 00:39:19,820 This is the figure of that I used for the cover of the book. 645 00:39:19,820 --> 00:39:23,240 The artist chose it and extracted it. 646 00:39:23,240 --> 00:39:25,725 She got it from it. 647 00:39:25,725 --> 00:39:28,980 And this is the same picture from Nauta, 648 00:39:28,980 --> 00:39:37,730 where he's left the caudate there, caudate nucleus. 649 00:39:37,730 --> 00:39:42,050 And here the hippocampal formation in place, 650 00:39:42,050 --> 00:39:44,900 and there's the amygdala. 651 00:39:44,900 --> 00:39:48,380 Here he's removed those. 652 00:39:48,380 --> 00:39:50,920 Because what he's showing here is 653 00:39:50,920 --> 00:39:54,850 fibers of the internal capsule, and the caudate 654 00:39:54,850 --> 00:39:57,296 is always medial to the internal capsule. 655 00:39:57,296 --> 00:40:01,610 He's removed the containment in this section. 656 00:40:01,610 --> 00:40:04,170 And here with all those structures removed, 657 00:40:04,170 --> 00:40:10,550 you see the-- we call it the corona radiata fibers. 658 00:40:10,550 --> 00:40:14,650 And these fibers here from Meyer's loop 659 00:40:14,650 --> 00:40:17,110 are part of the optic radiation. 660 00:40:17,110 --> 00:40:19,940 It's the part that represents the upper visual field. 661 00:40:19,940 --> 00:40:23,125 So if you get a temporal lobe injury in humans, 662 00:40:23,125 --> 00:40:28,350 you seem to be very far from the visual cortex, which is here. 663 00:40:28,350 --> 00:40:32,220 But the fibers that go to the visual cortex 664 00:40:32,220 --> 00:40:34,500 go through part of the temporal lobe there. 665 00:40:34,500 --> 00:40:37,420 At least the ones representing the upper visual field. 666 00:40:37,420 --> 00:40:40,816 So you can get cortical blindness 667 00:40:40,816 --> 00:40:43,465 in the upper visual field from a temporal lobe 668 00:40:43,465 --> 00:40:46,470 injury because of that. 669 00:40:46,470 --> 00:40:51,040 Or a tumor in the temporal lobe can cause that. 670 00:40:51,040 --> 00:40:53,950 And it's easily understood once you understand 671 00:40:53,950 --> 00:40:58,110 the topography of the optic radiations. 672 00:40:58,110 --> 00:40:59,780 And these pictures are just meant 673 00:40:59,780 --> 00:41:05,420 to help you understand that concept. 674 00:41:05,420 --> 00:41:08,740 And you see here, I'll have some of them-- 675 00:41:08,740 --> 00:41:10,540 several peduncles in the pyramidal tract. 676 00:41:13,306 --> 00:41:17,200 And of course, many of those pyramidal tract fibers 677 00:41:17,200 --> 00:41:20,370 are coming from the central cortex. 678 00:41:20,370 --> 00:41:22,920 Motor cortex here. 679 00:41:22,920 --> 00:41:24,390 Sensory cortex here. 680 00:41:31,230 --> 00:41:33,990 So what are two methods used by neuroscientists 681 00:41:33,990 --> 00:41:37,922 to map multiple visual areas in the cortex? 682 00:41:37,922 --> 00:41:41,060 And why do we believe the human brain contains 683 00:41:41,060 --> 00:41:45,941 more than the 32 areas described for those in this monkey? 684 00:41:45,941 --> 00:41:46,440 Yes? 685 00:42:09,970 --> 00:42:10,570 Exactly. 686 00:42:10,570 --> 00:42:14,090 The relationship is a pretty clear one. 687 00:42:14,090 --> 00:42:17,790 Here's the relationships you're talking about. 688 00:42:17,790 --> 00:42:23,530 And we plot neocortical surface area 689 00:42:23,530 --> 00:42:27,050 against a number of visual areas. 690 00:42:27,050 --> 00:42:30,390 In either logarithmic or linear coordinates. 691 00:42:30,390 --> 00:42:35,340 See here on the log, log scale, you get a pretty good line. 692 00:42:35,340 --> 00:42:42,660 It's not totally precise, but there 693 00:42:42,660 --> 00:42:45,240 is a pretty good correspondence. 694 00:42:45,240 --> 00:42:50,220 The animals with very small cortex have fewer variates. 695 00:42:50,220 --> 00:42:52,240 Some people have taken that to extremes 696 00:42:52,240 --> 00:42:56,390 and suggested that the tiny, tiny little shrew 697 00:42:56,390 --> 00:42:59,970 brains and rodent brains should only have just a few. 698 00:42:59,970 --> 00:43:05,890 It turns out they have more than that. 699 00:43:05,890 --> 00:43:17,320 So they show here, for example, mass shrews having one area. 700 00:43:17,320 --> 00:43:24,680 Here they have mouse, showing only two, or maybe three areas. 701 00:43:24,680 --> 00:43:26,990 Turns out not to be true. 702 00:43:26,990 --> 00:43:31,490 So these were based on early studies, where they simply 703 00:43:31,490 --> 00:43:35,720 hadn't applied all these methods that I'm talking about. 704 00:43:35,720 --> 00:43:40,820 Now, here it was the usual method of recording, 705 00:43:40,820 --> 00:43:42,950 and here they're penetrating to the microbe. 706 00:43:42,950 --> 00:43:45,410 This is a medial view of the owl monkey, 707 00:43:45,410 --> 00:43:49,167 and it shows penetrations through this one area, 708 00:43:49,167 --> 00:43:50,375 and mapping the visual field. 709 00:43:50,375 --> 00:43:53,650 And they find a complete map of a retina view. 710 00:43:53,650 --> 00:43:54,550 OK? 711 00:43:54,550 --> 00:43:57,380 So they do that, all these different areas. 712 00:43:57,380 --> 00:44:01,880 This was done by Allman and often working with John Kaas. 713 00:44:01,880 --> 00:44:04,840 They've done it together in a number of animals, 714 00:44:04,840 --> 00:44:08,300 and separately with other animals. 715 00:44:08,300 --> 00:44:11,132 Much of the work on the owl monkey was done by Allman, 716 00:44:11,132 --> 00:44:13,860 and I've used his pictures here. 717 00:44:13,860 --> 00:44:16,570 You see all these areas. 718 00:44:16,570 --> 00:44:20,010 How this is all visual cortex. 719 00:44:20,010 --> 00:44:23,050 Here we call this inferotemporal cortex. 720 00:44:23,050 --> 00:44:29,534 Inferior gyrus of the temporal lobe. 721 00:44:29,534 --> 00:44:32,360 Of course, this is occipital, and this 722 00:44:32,360 --> 00:44:33,930 is posterior [INAUDIBLE]. 723 00:44:33,930 --> 00:44:37,470 So all of these areas have complete representation 724 00:44:37,470 --> 00:44:43,450 of the visual field, getting input from the thalamus. 725 00:44:43,450 --> 00:44:46,090 Let's answer another question right now. 726 00:44:46,090 --> 00:44:49,950 Each of these areas gets input from two major sources. 727 00:44:49,950 --> 00:44:53,760 What are they? 728 00:44:53,760 --> 00:44:56,760 From thalamus, and most of these we 729 00:44:56,760 --> 00:45:00,470 know come from geniculate body. 730 00:45:00,470 --> 00:45:04,890 The rest of them are coming from the lateral thalamus. 731 00:45:04,890 --> 00:45:09,160 The different subnuclei of the pulvinar. 732 00:45:09,160 --> 00:45:11,490 OK? 733 00:45:11,490 --> 00:45:13,174 What's the other source of inputs? 734 00:45:17,340 --> 00:45:19,756 Transcortical. 735 00:45:19,756 --> 00:45:24,300 They get inputs from the striate here. 736 00:45:24,300 --> 00:45:30,710 So one of the methods used to map, then-- of course, 737 00:45:30,710 --> 00:45:32,085 the two methods I'm talking about 738 00:45:32,085 --> 00:45:36,450 are electrophysiology, which is shown here on the left side, 739 00:45:36,450 --> 00:45:37,880 and anatomy. 740 00:45:37,880 --> 00:45:43,800 And here is this picture I included in the book. 741 00:45:43,800 --> 00:45:45,455 Beautiful study of the mouse. 742 00:45:45,455 --> 00:45:46,890 And look what they've done. 743 00:45:46,890 --> 00:45:51,570 They've taken three fluorescent tracer substances 744 00:45:51,570 --> 00:45:57,030 and put them into separate areas along the caudal part 745 00:45:57,030 --> 00:45:58,760 of the first visual area. 746 00:45:58,760 --> 00:45:59,490 Striate cortex. 747 00:46:02,360 --> 00:46:04,450 And they let the animal survive for a while, 748 00:46:04,450 --> 00:46:07,240 so you get transport of those fluorescent labels 749 00:46:07,240 --> 00:46:08,635 to various terminal areas. 750 00:46:08,635 --> 00:46:11,910 And look what they're getting. 751 00:46:11,910 --> 00:46:16,820 This topography is repeated there, and there, there. 752 00:46:16,820 --> 00:46:26,160 You see several-- 1, 2, 3, 4, 5, 6, 7, 8, 9, 753 00:46:26,160 --> 00:46:30,185 and then additional areas where the topography isn't 754 00:46:30,185 --> 00:46:32,210 as precise, but it is still there. 755 00:46:32,210 --> 00:46:34,590 You see an enlargement of a [INAUDIBLE] 756 00:46:34,590 --> 00:46:37,005 getting sparse input here in the [INAUDIBLE] 757 00:46:37,005 --> 00:46:39,610 area on the medial side. 758 00:46:39,610 --> 00:46:41,580 But you see there still is topography. 759 00:46:41,580 --> 00:46:46,610 You see the rex axons, the green axons, and the yellow axons. 760 00:46:46,610 --> 00:46:50,530 Not as precise, but it's still there. 761 00:46:50,530 --> 00:46:55,910 So they these 10 different areas in this mouse. 762 00:46:55,910 --> 00:46:59,430 Just to show you how the data changes, 763 00:46:59,430 --> 00:47:05,160 here it says two or three, we get 10. 764 00:47:05,160 --> 00:47:05,660 OK? 765 00:47:09,510 --> 00:47:11,393 And this is just a flattened view 766 00:47:11,393 --> 00:47:18,180 of the cortex that shows where they put those injections in. 767 00:47:18,180 --> 00:47:19,590 This is mouse, yes. 768 00:47:22,910 --> 00:47:25,972 [? Burkhalter. ?] His lab is where they did this. 769 00:47:25,972 --> 00:47:29,960 But he obviously had really good command of this method, 770 00:47:29,960 --> 00:47:32,650 and was able to get some very beautiful results. 771 00:47:36,090 --> 00:47:39,010 And this is just a picture to illustrate 772 00:47:39,010 --> 00:47:43,510 that they keep seeing V1 and V2 in all the different mammals, 773 00:47:43,510 --> 00:47:45,238 including the marsupials. 774 00:47:45,238 --> 00:47:46,910 OK? 775 00:47:46,910 --> 00:47:49,890 That's all that's illustrating. 776 00:47:49,890 --> 00:47:52,364 Putting them on a cladogram. 777 00:47:52,364 --> 00:47:53,780 And this is another one where they 778 00:47:53,780 --> 00:47:59,070 show that most of those groups have area MT. 779 00:47:59,070 --> 00:48:02,308 They have a myelinated area. 780 00:48:02,308 --> 00:48:05,080 It's a pretty direct visual path. 781 00:48:05,080 --> 00:48:06,840 As does the striate cortex. 782 00:48:06,840 --> 00:48:09,052 But you don't find it in the marsupials. 783 00:48:12,590 --> 00:48:18,180 And this is adding, besides V1 and V2, is the ancient areas. 784 00:48:18,180 --> 00:48:20,612 Even in the hedgehogs you see it. 785 00:48:20,612 --> 00:48:23,616 But you also always see an [INAUDIBLE] area. 786 00:48:23,616 --> 00:48:29,320 You always see two somatosensory areas, 787 00:48:29,320 --> 00:48:35,165 and you usually, but not always see a motor area. 788 00:48:35,165 --> 00:48:37,426 You don't always see a motor area separate 789 00:48:37,426 --> 00:48:38,592 from the somatosensory area. 790 00:48:41,680 --> 00:48:42,905 In the opossum, for example. 791 00:48:47,220 --> 00:48:50,280 And I think we talked about that once before. 792 00:48:50,280 --> 00:48:53,510 The amalgam of the two areas. 793 00:48:53,510 --> 00:48:55,795 Because motor cortex appears to have originated 794 00:48:55,795 --> 00:48:59,976 as a somatosensory area, then it became specialized 795 00:48:59,976 --> 00:49:04,393 for the more direct connections to the spinal cord, 796 00:49:04,393 --> 00:49:07,972 the motor function. 797 00:49:07,972 --> 00:49:09,840 OK, we've already answered this. 798 00:49:09,840 --> 00:49:12,910 So next time we'll start with the major transcortical 799 00:49:12,910 --> 00:49:13,640 connections. 800 00:49:13,640 --> 00:49:15,050 It won't take very long. 801 00:49:15,050 --> 00:49:19,340 Just read it, and where it's different from other treatments 802 00:49:19,340 --> 00:49:24,300 in the current literature is I'm pointing out 803 00:49:24,300 --> 00:49:26,840 something that was neglected by other people. 804 00:49:26,840 --> 00:49:29,280 They talk about always two pathways. 805 00:49:29,280 --> 00:49:34,720 They were influenced by other early work that came from MIT. 806 00:49:34,720 --> 00:49:36,090 The two visual systems. 807 00:49:36,090 --> 00:49:38,492 So there's always two visual pathways. 808 00:49:38,492 --> 00:49:41,990 The object location, object identification. 809 00:49:41,990 --> 00:49:43,895 So they just neglected the third one, 810 00:49:43,895 --> 00:49:46,160 and Nauta had pointed it out. 811 00:49:46,160 --> 00:49:49,390 But he wasn't focused visual systems. 812 00:49:49,390 --> 00:49:52,860 But there in his results, published results, 813 00:49:52,860 --> 00:49:56,010 after he died, I found these results, 814 00:49:56,010 --> 00:50:01,390 and I've included in my book as a medial pathway, 815 00:50:01,390 --> 00:50:03,160 going towards the hippocampal formation. 816 00:50:03,160 --> 00:50:06,016 Terminates in the parahippocampal areas. 817 00:50:06,016 --> 00:50:09,680 So we'll just go over that quickly next time.