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 --> 00:00:17,239 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:17,239 --> 00:00:17,864 at ocw.mit.edu. 8 00:00:23,034 --> 00:00:24,700 PROFESSOR: At the end of the last class, 9 00:00:24,700 --> 00:00:30,890 I mentioned that this invasion of the endbrain by visual 10 00:00:30,890 --> 00:00:35,690 pathways-- we know mostly that even though there 11 00:00:35,690 --> 00:00:38,290 was a direct pathway, it was very small-- the one 12 00:00:38,290 --> 00:00:41,130 through the geniculate body, very small early on. 13 00:00:41,130 --> 00:00:45,700 Major routes into the endbrain. 14 00:00:45,700 --> 00:00:50,440 They began at the tectum, also the pretectal area, which 15 00:00:50,440 --> 00:00:53,790 projected into thalamic areas, which 16 00:00:53,790 --> 00:00:57,270 then projected to the endbrain. 17 00:00:57,270 --> 00:01:00,030 I asked there at the end of the class, what 18 00:01:00,030 --> 00:01:02,150 would be the adaptive advantages of that? 19 00:01:02,150 --> 00:01:03,525 Why would it invade the endbrain? 20 00:01:06,570 --> 00:01:12,010 First, I tried to give them a comical answer-- 21 00:01:12,010 --> 00:01:14,520 it's a way to provide better information to the striatum. 22 00:01:14,520 --> 00:01:19,540 Remember, visual information can reach the striatum directly 23 00:01:19,540 --> 00:01:21,410 from the overthalamus. 24 00:01:21,410 --> 00:01:26,860 Those structures weren't precisely topographic, 25 00:01:26,860 --> 00:01:30,500 and the striatum wasn't the structure 26 00:01:30,500 --> 00:01:36,730 that made really good topography as easy to form in evolution. 27 00:01:36,730 --> 00:01:38,970 That's my interpretation. 28 00:01:38,970 --> 00:01:42,000 Obviously, that happened mostly in the cortex. 29 00:01:42,000 --> 00:01:46,885 In the cortex, you get this highly topographic mapping 30 00:01:46,885 --> 00:01:49,790 of the visual world, and those pathways 31 00:01:49,790 --> 00:01:53,520 came by way of the membrane and directly 32 00:01:53,520 --> 00:01:56,410 from the geniculate body. 33 00:01:56,410 --> 00:02:03,800 That enabled a lot better acuity for the learning 34 00:02:03,800 --> 00:02:05,760 that the endbrain was capable of, 35 00:02:05,760 --> 00:02:09,380 especially by means of its pathways to where? 36 00:02:09,380 --> 00:02:14,530 Two different places-- to the striatum for habit learning, 37 00:02:14,530 --> 00:02:16,510 and to the hippocampal formation, 38 00:02:16,510 --> 00:02:21,053 for learning about locations of the animal 39 00:02:21,053 --> 00:02:23,594 in their environment. 40 00:02:23,594 --> 00:02:25,640 Not the locations of other animals-- 41 00:02:25,640 --> 00:02:28,380 the location of the animal whose brain we're talking about. 42 00:02:33,000 --> 00:02:38,770 The cognitive functions were that route to the hippocampus, 43 00:02:38,770 --> 00:02:42,370 replace information as a major part of our cognitive ability, 44 00:02:42,370 --> 00:02:46,310 our memory formation, but also another kind of memory-- 45 00:02:46,310 --> 00:02:50,830 it provided a visual route to the amygdala, which is really 46 00:02:50,830 --> 00:02:54,400 part of the striatum, the way I see it-- 47 00:02:54,400 --> 00:02:57,860 at least a caudal output for the striatum. 48 00:02:57,860 --> 00:03:01,272 It functions like a striatum with the learning 49 00:03:01,272 --> 00:03:02,355 of avoidance and approach. 50 00:03:05,520 --> 00:03:08,950 Also binocular vision, which we won't talk very much about now, 51 00:03:08,950 --> 00:03:12,680 but that was important, too, because the neocortex made 52 00:03:12,680 --> 00:03:18,900 possible a lot better binocular vision by especially 53 00:03:18,900 --> 00:03:20,440 stereopsis. 54 00:03:20,440 --> 00:03:22,940 Slight difference in the visual image in the two eyes 55 00:03:22,940 --> 00:03:26,040 because the information from the right eye and left eye is kept 56 00:03:26,040 --> 00:03:27,920 separate, all the way up to the cortex, 57 00:03:27,920 --> 00:03:31,715 where then, you can combine that information and get depth. 58 00:03:36,580 --> 00:03:40,490 At the end of that chapter 20, I mentioned-- 59 00:03:40,490 --> 00:03:42,950 I believe it's in chapter 20-- I mentioned some 60 00:03:42,950 --> 00:03:44,956 of the expansions and specializations 61 00:03:44,956 --> 00:03:50,555 of the visual system, mainly midbrain tectum 62 00:03:50,555 --> 00:03:55,695 and the thalamocortical projections 63 00:03:55,695 --> 00:03:58,340 of the visual system. 64 00:03:58,340 --> 00:04:01,200 These are the two major structures, 65 00:04:01,200 --> 00:04:02,810 and we're going to look at that today. 66 00:04:08,730 --> 00:04:11,760 We'll be talking a lot more about transcortical pathways 67 00:04:11,760 --> 00:04:13,445 in the following class. 68 00:04:15,980 --> 00:04:19,930 I don't deal in the book with the tremendous differences 69 00:04:19,930 --> 00:04:21,700 among animals in retinas. 70 00:04:21,700 --> 00:04:27,590 They develop many retinal specialization in animals. 71 00:04:27,590 --> 00:04:31,430 You don't need larger eyes just to get a larger retina 72 00:04:31,430 --> 00:04:36,999 and get more retina ganglion cells and more acuity that way. 73 00:04:36,999 --> 00:04:38,540 What else do you need large eyes for? 74 00:04:42,290 --> 00:04:44,740 Bring in more light. 75 00:04:44,740 --> 00:04:47,043 Why do you buy a camera with a big lens rather than 76 00:04:47,043 --> 00:04:48,210 a small lens? 77 00:04:48,210 --> 00:04:51,210 Brings in more light. 78 00:04:51,210 --> 00:04:55,090 If you want to get a camera that can take pictures in very dim 79 00:04:55,090 --> 00:05:00,880 light, get a camera with a very large lens opening, 80 00:05:00,880 --> 00:05:05,010 like F1.8 or something like that. 81 00:05:05,010 --> 00:05:07,590 It'll take in a lot of light. 82 00:05:07,590 --> 00:05:09,152 Question. 83 00:05:09,152 --> 00:05:15,104 AUDIENCE: For animals, does that [INAUDIBLE] 84 00:05:15,104 --> 00:05:17,088 have a forward configuration in their eyes? 85 00:05:21,070 --> 00:05:22,470 PROFESSOR: Excellent question. 86 00:05:22,470 --> 00:05:25,760 We know that animals with forward-looking eyes 87 00:05:25,760 --> 00:05:28,585 are usually predators and primates, 88 00:05:28,585 --> 00:05:31,440 and primates are usually predators, too, but not 89 00:05:31,440 --> 00:05:32,702 all of them. 90 00:05:32,702 --> 00:05:35,580 Some of them are fruit-gathering primates. 91 00:05:35,580 --> 00:05:38,490 But they also need good binocular vision 92 00:05:38,490 --> 00:05:40,680 so they have forward-facing eyes, too. 93 00:05:43,270 --> 00:05:47,450 But what about these animals with the eyes like the hamster? 94 00:05:47,450 --> 00:05:52,680 It's got eyes that look 60 degrees out and 30 degrees in. 95 00:05:52,680 --> 00:05:55,200 That's the way their eyes look. 96 00:05:55,200 --> 00:05:57,030 That's the natural position of the eyes. 97 00:05:57,030 --> 00:05:58,840 I've measured it in the hamster. 98 00:05:58,840 --> 00:06:02,170 It's pretty similar in other little rodents. 99 00:06:02,170 --> 00:06:05,780 They do have an area of binocular vision. 100 00:06:05,780 --> 00:06:14,650 There's about at least 30-degree overlap in that central area. 101 00:06:14,650 --> 00:06:19,290 The center of it is 30 degrees above. 102 00:06:19,290 --> 00:06:25,850 They do have binocular vision, but it's pretty rudimentary 103 00:06:25,850 --> 00:06:27,830 compared to the primates. 104 00:06:27,830 --> 00:06:33,220 Also, they don't have the high acuity that primates have. 105 00:06:33,220 --> 00:06:35,710 But it's still important to them. 106 00:06:35,710 --> 00:06:44,140 I've looked at hamster behavior a lot, and things five feet 107 00:06:44,140 --> 00:06:48,840 or even two feet and 30 feet away, 108 00:06:48,840 --> 00:06:50,680 they don't [? discern it ?] very well. 109 00:06:53,410 --> 00:06:56,770 But for things near them, they definitely can judge vision. 110 00:06:56,770 --> 00:07:00,520 They won't leap-- sometimes they do, 111 00:07:00,520 --> 00:07:04,761 but usually, they won't jump into places 112 00:07:04,761 --> 00:07:06,760 that are too dangerous because they're too high. 113 00:07:06,760 --> 00:07:09,730 They can see the depth well enough. 114 00:07:09,730 --> 00:07:13,820 It doesn't mean stereopsis cues, though-- it could just 115 00:07:13,820 --> 00:07:19,170 be the various other cues, like when they move their head, 116 00:07:19,170 --> 00:07:30,420 the parallax that you get-- there's various cues to depth 117 00:07:30,420 --> 00:07:32,980 that if you study in a sensation and perception class 118 00:07:32,980 --> 00:07:37,305 here at MIT, you'll learn about multiple different cues 119 00:07:37,305 --> 00:07:40,445 for depth that don't involve stereopsis. 120 00:07:45,770 --> 00:07:49,380 Now we want to look at the retinal perceptions. 121 00:07:49,380 --> 00:07:53,650 It's a pattern you find in all the mammals, 122 00:07:53,650 --> 00:07:56,490 and I should add that it's really 123 00:07:56,490 --> 00:07:58,320 similar in all of the vertebrates. 124 00:08:02,520 --> 00:08:11,100 This is the picture I showed in the last class of the cartoon 125 00:08:11,100 --> 00:08:16,920 of the main optic tract and the accessory optic track here. 126 00:08:16,920 --> 00:08:18,760 Now we want to look in a little more detail 127 00:08:18,760 --> 00:08:23,580 at the layout of that system-- the suprachiasmatic nucleus 128 00:08:23,580 --> 00:08:26,020 to the two geniculate nuclei. 129 00:08:26,020 --> 00:08:27,570 The pretectal region, where there's 130 00:08:27,570 --> 00:08:29,692 several nuclei where they terminate-- 131 00:08:29,692 --> 00:08:31,650 superior colliculus. 132 00:08:31,650 --> 00:08:43,799 I 133 00:08:43,799 --> 00:08:46,310 Look at the retinal projection invertebrates, 134 00:08:46,310 --> 00:08:49,240 the layout of the optic tract. 135 00:08:49,240 --> 00:08:51,750 Look at them in several different ways 136 00:08:51,750 --> 00:08:53,366 of looking at it. 137 00:08:53,366 --> 00:08:55,660 We'll talk about species differences 138 00:08:55,660 --> 00:09:00,450 and relative size of structures because qualitatively, they all 139 00:09:00,450 --> 00:09:05,150 have the same basic layout, but there are large species 140 00:09:05,150 --> 00:09:10,030 differences in relative sizes as well as in the eyes 141 00:09:10,030 --> 00:09:14,890 are different too, so you have different levels 142 00:09:14,890 --> 00:09:21,160 of acuity in vision are possible in these different species. 143 00:09:21,160 --> 00:09:25,300 We'll look a little bit at architectural differences, 144 00:09:25,300 --> 00:09:30,930 especially in the geniculate body and the optic tectum. 145 00:09:30,930 --> 00:09:35,210 We'll look at lamination in midbrain tectum. 146 00:09:35,210 --> 00:09:37,680 We'll also look at lamination in the geniculate body. 147 00:09:42,030 --> 00:09:44,540 And finally, we'll look at topography. 148 00:09:44,540 --> 00:09:47,700 I know when you first get all this, 149 00:09:47,700 --> 00:09:50,300 you get a little overwhelmed by all structures and everything, 150 00:09:50,300 --> 00:09:55,540 so I'm not asking you to memorize the topography. 151 00:09:55,540 --> 00:09:57,440 I will present to you in a way that 152 00:09:57,440 --> 00:09:59,280 does make it pretty easy to learn. 153 00:10:03,870 --> 00:10:04,950 These are the questions. 154 00:10:04,950 --> 00:10:08,490 I put a list of questions online for you. 155 00:10:11,510 --> 00:10:13,690 These are things we've dealt with before, these two 156 00:10:13,690 --> 00:10:14,300 questions. 157 00:10:14,300 --> 00:10:17,980 Let's just see if any of you have an idea about it. 158 00:10:17,980 --> 00:10:21,512 First of all, what's the first structure reached by the axons 159 00:10:21,512 --> 00:10:22,845 from the retinal ganglion cells. 160 00:10:25,650 --> 00:10:28,320 Ganglion cells project through the nerve. 161 00:10:28,320 --> 00:10:30,040 We start calling it the tract when 162 00:10:30,040 --> 00:10:33,186 it joins with the rest of the diencephalon. 163 00:10:33,186 --> 00:10:34,310 What's the first structure? 164 00:10:37,480 --> 00:10:38,210 Exactly. 165 00:10:38,210 --> 00:10:40,645 Suprachiasmatic nucleus, right above the crossing 166 00:10:40,645 --> 00:10:42,660 of the axons. 167 00:10:42,660 --> 00:10:45,471 It's gotta be the first one. 168 00:10:45,471 --> 00:10:48,717 AUDIENCE: [INAUDIBLE]. 169 00:10:48,717 --> 00:10:50,925 PROFESSOR: It's part of the hypothalamus, definitely. 170 00:10:54,670 --> 00:10:56,780 The area in front of that region, 171 00:10:56,780 --> 00:11:01,570 we call preoptic area of the hypothalamus 172 00:11:01,570 --> 00:11:03,755 because it's in front of the optic chiasm. 173 00:11:07,640 --> 00:11:10,220 Actually, we talked about the anterior hypothalamic nucleus 174 00:11:10,220 --> 00:11:11,470 and then the preoptic nucleus. 175 00:11:13,720 --> 00:11:15,790 I might apply my first statement a little bit. 176 00:11:19,410 --> 00:11:21,640 The forebrain subdivision you've just named, 177 00:11:21,640 --> 00:11:26,410 it's the hypothalamus and the major terminal nucleus 178 00:11:26,410 --> 00:11:29,760 in that subdivision is the suprachiasmatic nucleus. 179 00:11:29,760 --> 00:11:32,310 Now remember, there's some [? store ?] over there, 180 00:11:32,310 --> 00:11:36,260 too, that I showed you last time. 181 00:11:36,260 --> 00:11:41,150 It does project the two immediately adjoining parts 182 00:11:41,150 --> 00:11:43,770 of the hypothalamus. 183 00:11:43,770 --> 00:11:47,050 We know most about that suprachiasmatic nucleus. 184 00:11:47,050 --> 00:11:49,060 There's very little known about the functions 185 00:11:49,060 --> 00:11:52,011 of the sparse projections. 186 00:11:52,011 --> 00:11:53,510 People tend to think that they don't 187 00:11:53,510 --> 00:11:56,490 play any major roles, that's why they're so sparse. 188 00:11:59,920 --> 00:12:03,880 I'm not convinced of that. 189 00:12:03,880 --> 00:12:05,355 They could play important roles. 190 00:12:09,570 --> 00:12:12,060 The one thing that makes me doubt it a little bit 191 00:12:12,060 --> 00:12:14,040 is just that there's variability. 192 00:12:14,040 --> 00:12:16,304 When I study the retinal projections 193 00:12:16,304 --> 00:12:17,720 in a number of different hamsters, 194 00:12:17,720 --> 00:12:21,950 I do get differences in these very sparse projections. 195 00:12:21,950 --> 00:12:26,380 Some animals I see more, some I see less, 196 00:12:26,380 --> 00:12:27,710 but they're always there. 197 00:12:31,250 --> 00:12:36,510 The next question is, what's the major difference 198 00:12:36,510 --> 00:12:39,360 in the nature of the projections of the dorsal thalamus 199 00:12:39,360 --> 00:12:44,080 on the one hand and the ventral thalamus or the epithalamus? 200 00:12:44,080 --> 00:12:48,280 That is, after you go past the suprachiasmatic nucleus, 201 00:12:48,280 --> 00:12:50,510 the axons go up the side of the diencephalon 202 00:12:50,510 --> 00:12:55,370 and they reach the subthalamus just above the hypothalamus. 203 00:12:55,370 --> 00:12:57,970 Then they reach the dorsal thalamus, 204 00:12:57,970 --> 00:13:00,325 then they reach the epithalamus-- 205 00:13:00,325 --> 00:13:02,730 the pretectal nuclei in the epithalamus. 206 00:13:05,350 --> 00:13:06,980 There's a big difference, though, 207 00:13:06,980 --> 00:13:10,230 in the nature of the projections of the dorsal thalamus 208 00:13:10,230 --> 00:13:11,920 and those other groups. 209 00:13:11,920 --> 00:13:13,238 What is that difference? 210 00:13:13,238 --> 00:13:14,194 AUDIENCE: [INAUDIBLE]. 211 00:13:21,074 --> 00:13:21,865 PROFESSOR: Exactly. 212 00:13:21,865 --> 00:13:24,250 The biggest difference is what she just 213 00:13:24,250 --> 00:13:28,635 said-- the dorsal thalamus and all the major cell 214 00:13:28,635 --> 00:13:35,100 groups-- at least the neothalamus, the more recent-- 215 00:13:35,100 --> 00:13:38,330 the dorsal thalamus, like the lateral geniculate body, 216 00:13:38,330 --> 00:13:40,860 but the same thing holds true for the ventral nucleus, 217 00:13:40,860 --> 00:13:46,150 medial dorsal nucleus, medial geniculate body. 218 00:13:46,150 --> 00:13:50,345 It projects to cortex, mainly to neocortex. 219 00:13:50,345 --> 00:13:51,960 It goes to the endbrain. 220 00:13:54,930 --> 00:13:57,940 Some neurons, some axons will have collaterals 221 00:13:57,940 --> 00:14:00,390 in the striatum on their way to the endbrain, 222 00:14:00,390 --> 00:14:03,150 but the major projection is to the endbrain. 223 00:14:03,150 --> 00:14:09,070 Those other structures-- subthalamus and epithalamus-- 224 00:14:09,070 --> 00:14:11,040 don't project to the endbrain. 225 00:14:13,940 --> 00:14:18,750 There are reports that they do, but modern techniques 226 00:14:18,750 --> 00:14:21,000 have never been able to verify that. 227 00:14:21,000 --> 00:14:24,480 They don't project to neocortex. 228 00:14:24,480 --> 00:14:30,670 In fact, besides some ascending projections, 229 00:14:30,670 --> 00:14:32,990 they have a lot of descending projections. 230 00:14:37,274 --> 00:14:38,440 That's the major difference. 231 00:14:44,390 --> 00:14:47,700 Last time, I mentioned the epithalamus 232 00:14:47,700 --> 00:14:54,450 as a caudalmost diencephalic segment, or neuromere. 233 00:14:54,450 --> 00:14:56,505 It includes cell groups for the optic tract, 234 00:14:56,505 --> 00:14:58,680 its dense terminations. 235 00:14:58,680 --> 00:15:01,635 Again, what do we call those areas of termination? 236 00:15:06,540 --> 00:15:10,180 We call them certain nuclei, depending on where they are. 237 00:15:10,180 --> 00:15:15,850 They're in front of the tectum, so we call them pretectal. 238 00:15:18,610 --> 00:15:20,704 They are rather different, these different groups, 239 00:15:20,704 --> 00:15:22,120 and they have different functions, 240 00:15:22,120 --> 00:15:24,320 but we lump them together because they're 241 00:15:24,320 --> 00:15:27,400 all in that same region called pretectal nuclei. 242 00:15:30,670 --> 00:15:32,730 This is two ways to look at it. 243 00:15:32,730 --> 00:15:35,180 Don't worry, I'll blow this up. 244 00:15:35,180 --> 00:15:42,470 Here's a cross section of a level through the diencephalon. 245 00:15:42,470 --> 00:15:44,580 This is actually behind the optic chiasm, 246 00:15:44,580 --> 00:15:48,200 but you see the optic tract covering 247 00:15:48,200 --> 00:15:52,390 most of the diencephalon, or 'tween brain, at this level. 248 00:15:52,390 --> 00:15:55,380 The pretectum up here, the dorsal thalamus 249 00:15:55,380 --> 00:15:58,720 with lateral geniculate is right there. 250 00:15:58,720 --> 00:16:01,560 Here's the subthalamus with ventral nucleus, 251 00:16:01,560 --> 00:16:03,370 a ventronucleic body there. 252 00:16:03,370 --> 00:16:05,590 There's hypothalamus. 253 00:16:05,590 --> 00:16:07,560 This is behind the optic chiasm. 254 00:16:07,560 --> 00:16:10,380 The optic tract covers all these. 255 00:16:10,380 --> 00:16:12,310 That's why that area is sometimes 256 00:16:12,310 --> 00:16:14,820 called optic thalamus, just because the axons 257 00:16:14,820 --> 00:16:18,630 of the optic tract cover it. 258 00:16:18,630 --> 00:16:21,120 These are the subdivisions written 259 00:16:21,120 --> 00:16:26,530 as the names for their neuromeres. 260 00:16:26,530 --> 00:16:28,650 Now we know the hypothalamus is actually 261 00:16:28,650 --> 00:16:31,760 two or three different neuromeres. 262 00:16:31,760 --> 00:16:34,200 We call this the ventrothalamus, then in the adult, 263 00:16:34,200 --> 00:16:37,050 we call subthalamus. 264 00:16:37,050 --> 00:16:40,170 Then the dorsal thalamus, then the epithalamus. 265 00:16:40,170 --> 00:16:43,150 But note there's another way to look at the tract 266 00:16:43,150 --> 00:16:45,100 that I use for teaching purposes, 267 00:16:45,100 --> 00:16:46,490 but I think it's very useful. 268 00:16:46,490 --> 00:16:48,680 I just take the track all the way 269 00:16:48,680 --> 00:16:52,740 from the suprachiasmatic nucleus all the way to the tectum, just 270 00:16:52,740 --> 00:16:53,590 stretch it out. 271 00:16:56,200 --> 00:17:01,250 You see the retina would be way off here to the left, 272 00:17:01,250 --> 00:17:04,310 off the screen there to the left. 273 00:17:04,310 --> 00:17:06,285 There's the suprachiasmatic nucleus. 274 00:17:06,285 --> 00:17:08,559 It's more commonly abbreviated SCN, 275 00:17:08,559 --> 00:17:11,870 and here we call it just SCH, but could note it 276 00:17:11,870 --> 00:17:14,079 down either way. 277 00:17:14,079 --> 00:17:16,589 Then I just follow the accents. 278 00:17:16,589 --> 00:17:20,280 I straighten out the tract. 279 00:17:20,280 --> 00:17:22,260 I show what happens to them. 280 00:17:22,260 --> 00:17:28,010 The longest ones make it to the superior colliculus 281 00:17:28,010 --> 00:17:31,450 where they no longer travel mainly at the surface. 282 00:17:31,450 --> 00:17:34,810 The rest of the tract is mainly at the surface. 283 00:17:34,810 --> 00:17:38,580 There are some that travel internally. 284 00:17:38,580 --> 00:17:40,216 We call that the internal optic tract. 285 00:17:40,216 --> 00:17:43,270 But there are smaller numbers of axons that do that. 286 00:17:43,270 --> 00:17:44,920 The main ones travel on the surface 287 00:17:44,920 --> 00:17:48,220 except when they get in the sphere of the colliculus. 288 00:17:48,220 --> 00:17:52,410 Actually, they do travel at the surface of the colliculus early 289 00:17:52,410 --> 00:17:56,200 in development when they first get there, so then 290 00:17:56,200 --> 00:18:02,690 how do they end up down below those superficial layers? 291 00:18:02,690 --> 00:18:04,210 What has to happen? 292 00:18:04,210 --> 00:18:09,090 They're on the surface and then they're not, 293 00:18:09,090 --> 00:18:10,630 further development. 294 00:18:10,630 --> 00:18:15,930 Either the axons that were on the surface have to die off, 295 00:18:15,930 --> 00:18:22,430 or cells in colliculus migrate up through them. 296 00:18:22,430 --> 00:18:26,170 They're still migrating when this tract is forming. 297 00:18:26,170 --> 00:18:28,550 The latter interpretation appears 298 00:18:28,550 --> 00:18:34,330 to be true because you do see cell migrations going up 299 00:18:34,330 --> 00:18:37,840 to superficial gray occurring after the first axons have 300 00:18:37,840 --> 00:18:40,580 reached there, and when you look with stains 301 00:18:40,580 --> 00:18:43,110 that are capable see degeneration occurring, 302 00:18:43,110 --> 00:18:45,390 you don't see a lot of degeneration. 303 00:18:47,857 --> 00:18:49,690 We think it's actually doing cell migration. 304 00:18:52,690 --> 00:18:55,750 Here you see that it looks like they're branching off. 305 00:18:55,750 --> 00:18:57,630 Let's do it this way. 306 00:18:57,630 --> 00:18:59,665 Here's that first picture again. 307 00:18:59,665 --> 00:19:01,250 I'm going to blow it up. 308 00:19:01,250 --> 00:19:03,310 But it's the same thing, and I'd point out 309 00:19:03,310 --> 00:19:06,830 here ventral thalamus is not the ventral nucleus 310 00:19:06,830 --> 00:19:08,870 of the dorsal thalamus. 311 00:19:08,870 --> 00:19:12,800 It's really subthalamus. 312 00:19:12,800 --> 00:19:16,620 The ventral nucleus is this nucleus up in here, 313 00:19:16,620 --> 00:19:19,400 part of the dorsal thalamus. 314 00:19:19,400 --> 00:19:22,470 Here I just show the places the optic tract terminates, 315 00:19:22,470 --> 00:19:27,000 you see the dorsal part of the lateral geniculate body. 316 00:19:27,000 --> 00:19:29,270 Remember, this is a rodent. 317 00:19:29,270 --> 00:19:38,171 The LP is not huge, but it's the rest of the lateral thalamus. 318 00:19:38,171 --> 00:19:39,587 Besides the geniculate bodies, you 319 00:19:39,587 --> 00:19:44,230 have lateral thalamic nuclei. 320 00:19:44,230 --> 00:19:47,750 The medial geniculate is another lateral thalamic nucleus. 321 00:19:51,550 --> 00:19:56,510 Here is a human 12 weeks post-conception. 322 00:20:00,630 --> 00:20:03,280 Three-month human fetus. 323 00:20:03,280 --> 00:20:06,630 There's the rodent, adult. 324 00:20:06,630 --> 00:20:10,110 Here's the human fetus. 325 00:20:10,110 --> 00:20:15,830 The adult human thalamus doesn't look like this at all. 326 00:20:18,880 --> 00:20:22,280 I just want to point out that it's really 327 00:20:22,280 --> 00:20:24,680 the same as the rodent. 328 00:20:24,680 --> 00:20:28,160 In fact, the embryo looks very similar. 329 00:20:28,160 --> 00:20:30,020 But then it changes. 330 00:20:30,020 --> 00:20:31,650 Why? 331 00:20:31,650 --> 00:20:35,440 Anybody figure that out? 332 00:20:35,440 --> 00:20:39,110 What happens to the human thalamus development 333 00:20:39,110 --> 00:20:42,502 after that first three months of life? 334 00:20:42,502 --> 00:20:44,210 The brain of that three-month human fetus 335 00:20:44,210 --> 00:20:51,670 is pretty similar to a hamster just after birth. 336 00:20:56,880 --> 00:20:59,750 But then something continues developing 337 00:20:59,750 --> 00:21:02,930 in the hamster in both the hamster and human, 338 00:21:02,930 --> 00:21:06,800 but mostly the human after that first three months. 339 00:21:10,540 --> 00:21:14,680 That means, by the way, the human at three months 340 00:21:14,680 --> 00:21:18,635 post-conception is like an early postnatal hamster. 341 00:21:18,635 --> 00:21:23,510 The hamster is born in the 16th day of gestation, 342 00:21:23,510 --> 00:21:25,450 just to give you prompts. 343 00:21:25,450 --> 00:21:28,540 But anyway, what happens? 344 00:21:28,540 --> 00:21:33,920 This nucleus labeled NL, the lateral nucleus, 345 00:21:33,920 --> 00:21:36,550 nucleus lateralus-- this is the posterior 346 00:21:36,550 --> 00:21:40,000 part of nucleus lateralus. 347 00:21:40,000 --> 00:21:44,260 That grows and grows and grows, and in primates, 348 00:21:44,260 --> 00:21:48,030 it really gets huge and we changed its name. 349 00:21:48,030 --> 00:21:50,380 We call only part of it the lateral posterior 350 00:21:50,380 --> 00:21:53,740 nucleus, like we call the whole thing in rodents-- 351 00:21:53,740 --> 00:21:59,040 the rest of it, we call the pulvinar, which means pillow. 352 00:21:59,040 --> 00:22:03,530 The pillow because it's bulging out so much-- 353 00:22:03,530 --> 00:22:09,710 because the cortex it projects to, even though it's there 354 00:22:09,710 --> 00:22:12,900 real early, it expands so much. 355 00:22:17,290 --> 00:22:19,030 A lot of people that talk about cortex 356 00:22:19,030 --> 00:22:21,950 just think the sensory input comes to it 357 00:22:21,950 --> 00:22:24,560 and then you go from one region and the other in the cortex 358 00:22:24,560 --> 00:22:26,690 and then you go out through the motor cortex. 359 00:22:26,690 --> 00:22:29,920 Not a very good, accurate picture, 360 00:22:29,920 --> 00:22:32,340 even though the majority of people in this building 361 00:22:32,340 --> 00:22:33,800 think like that. 362 00:22:33,800 --> 00:22:38,190 That's not really a good picture connections of the cortex. 363 00:22:38,190 --> 00:22:42,600 We'll be dealing with that, including some next class, 364 00:22:42,600 --> 00:22:45,200 but we'll continue dealing with that with the other systems. 365 00:22:48,030 --> 00:22:49,870 That's what happens. 366 00:22:49,870 --> 00:22:55,150 Otherwise, at this stage, these pictures are pretty similar. 367 00:22:55,150 --> 00:23:03,750 Remember, those divisions here happened because even 368 00:23:03,750 --> 00:23:10,440 a very early embryo, they show a side view with the segments. 369 00:23:10,440 --> 00:23:15,165 Remember the seven rhombomeres here and then a little segment 370 00:23:15,165 --> 00:23:16,915 we call the isthmus and then the midbrain, 371 00:23:16,915 --> 00:23:19,100 which is a pretty big segment, and then 372 00:23:19,100 --> 00:23:21,690 the epithalamus with the pretectal 373 00:23:21,690 --> 00:23:26,370 forming area forming here-- the venular forming here. 374 00:23:26,370 --> 00:23:29,690 And then dorsal thalamus, ventral thalamus 375 00:23:29,690 --> 00:23:35,500 or subthalamus, hypothalamus, which actually turns out 376 00:23:35,500 --> 00:23:36,625 to be several subdivisions. 377 00:23:43,040 --> 00:23:45,720 These are the questions we want to answer now. 378 00:23:45,720 --> 00:23:49,390 I want you to be able to name the five main optic tract 379 00:23:49,390 --> 00:23:51,546 termination areas in the order they're 380 00:23:51,546 --> 00:23:52,670 reached by the optic tract. 381 00:23:55,900 --> 00:24:00,560 So here they are, they already passed the suprachiasmatic, 382 00:24:00,560 --> 00:24:03,330 then you have the two geniculate bodies, 383 00:24:03,330 --> 00:24:06,440 then they get to the pretectal area here-- I show them 384 00:24:06,440 --> 00:24:10,154 on this picture-- and then finally, they turn caudally 385 00:24:10,154 --> 00:24:11,820 and they get to the superior colliculus. 386 00:24:11,820 --> 00:24:13,380 Those are the areas. 387 00:24:13,380 --> 00:24:20,091 One, suprachiasmatic, two, three, four, and five 388 00:24:20,091 --> 00:24:21,049 is for your colliculus. 389 00:24:26,620 --> 00:24:28,760 Then I ask what additional areas receive 390 00:24:28,760 --> 00:24:31,230 sparse retinal projections. 391 00:24:31,230 --> 00:24:33,510 Well, I already talked about some 392 00:24:33,510 --> 00:24:35,310 near the suprachiasmatic nucleus, 393 00:24:35,310 --> 00:24:37,070 but there's some other sparse projections 394 00:24:37,070 --> 00:24:41,240 in the hypothalamus that are someone variable from animal 395 00:24:41,240 --> 00:24:43,890 to animal, at least among the hamsters that I've studied. 396 00:24:43,890 --> 00:24:47,190 I expect it's true of other species, too. 397 00:24:47,190 --> 00:24:52,120 That would be projections to the LP nucleus here. 398 00:24:57,220 --> 00:24:58,980 There are other little projections 399 00:24:58,980 --> 00:25:04,460 near the main projections that are also a little bit variable. 400 00:25:04,460 --> 00:25:07,410 Then I say inputs from the right and left eyes 401 00:25:07,410 --> 00:25:11,128 terminate in different areas-- a separation 402 00:25:11,128 --> 00:25:15,400 that is especially important for creating binocular disparity 403 00:25:15,400 --> 00:25:20,800 cues for perceiving depth, visual objects. 404 00:25:20,800 --> 00:25:23,420 Describe the appearance of the distinct areas 405 00:25:23,420 --> 00:25:27,730 in the diencephalon of a small rodent and of a monkey. 406 00:25:27,730 --> 00:25:31,390 Here, we're talking about the layers in the geniculate body. 407 00:25:31,390 --> 00:25:35,960 In this picture, that stretched-out optic tract, 408 00:25:35,960 --> 00:25:38,650 I show that. 409 00:25:38,650 --> 00:25:40,300 There's the suprachiasmatic. 410 00:25:40,300 --> 00:25:42,860 Then they reach the subthalamus. 411 00:25:42,860 --> 00:25:49,070 This is the lateral geniculate body ventral portion-- often 412 00:25:49,070 --> 00:25:50,790 abbreviated just LGV. 413 00:25:53,480 --> 00:25:58,390 It's also abbreviated LGNV-- lateral geniculate nucleus 414 00:25:58,390 --> 00:26:00,880 ventral part. 415 00:26:00,880 --> 00:26:05,043 But notice here, these are axons from the contralateral eye 416 00:26:05,043 --> 00:26:07,280 that I'm drawing. 417 00:26:07,280 --> 00:26:10,965 I show a little area separated here by the dashed lines, 418 00:26:10,965 --> 00:26:14,400 and there at the ventral and dorsal geniculate bodies, where 419 00:26:14,400 --> 00:26:17,121 those accents don't go. 420 00:26:17,121 --> 00:26:19,090 They don't go there because they're 421 00:26:19,090 --> 00:26:22,050 getting input from the other eye. 422 00:26:22,050 --> 00:26:24,080 It's a laminated structure. 423 00:26:24,080 --> 00:26:25,940 Not so obvious in the rodent, but when 424 00:26:25,940 --> 00:26:30,020 you go to other animals-- here's a four-layer geniculate body, 425 00:26:30,020 --> 00:26:32,580 which you find in some species. 426 00:26:32,580 --> 00:26:36,350 Then you find that the contralateral eye is projecting 427 00:26:36,350 --> 00:26:40,240 to the outermost, the layer nearest the optic tract, 428 00:26:40,240 --> 00:26:44,230 then it skips a layer, then it projects to the next layer, 429 00:26:44,230 --> 00:26:46,840 and then to the last layer. 430 00:26:46,840 --> 00:26:52,200 It projects to one and three, not two and four. 431 00:26:52,200 --> 00:26:56,960 In primates, like monkeys-- not all primates, but at least 432 00:26:56,960 --> 00:27:02,540 monkeys and apes and humans-- you have six layers. 433 00:27:02,540 --> 00:27:06,430 Sometimes you see seven in some parts of the geniculate body, 434 00:27:06,430 --> 00:27:12,370 but usually, we number six, so we'll see that. 435 00:27:12,370 --> 00:27:17,210 Then the axons go through and over the LP, 436 00:27:17,210 --> 00:27:19,920 the lateral posterior nucleus. 437 00:27:19,920 --> 00:27:21,960 It's the rest of the lateral thalamus, 438 00:27:21,960 --> 00:27:24,990 the part that grows so big in humans. 439 00:27:24,990 --> 00:27:27,430 I show a few terminations there. 440 00:27:27,430 --> 00:27:31,729 It's somewhat variable, but they are there. 441 00:27:31,729 --> 00:27:32,895 They're sparse terminations. 442 00:27:35,670 --> 00:27:41,090 Again, we don't know what those do. 443 00:27:41,090 --> 00:27:45,920 Maybe we don't need to know because those stained neurons 444 00:27:45,920 --> 00:27:48,680 where those sparse projections occur 445 00:27:48,680 --> 00:27:55,700 get very heavy visual input, but coming from the colliculus, 446 00:27:55,700 --> 00:27:58,930 not directly from the retina. 447 00:27:58,930 --> 00:28:03,230 One of the ideas about how the geniculate body appeared 448 00:28:03,230 --> 00:28:09,540 was just that-- these sparse, scattered projections 449 00:28:09,540 --> 00:28:13,120 that if some reduction of the colliculus occurred, 450 00:28:13,120 --> 00:28:16,760 they just sprouted more there and that was adapted. 451 00:28:16,760 --> 00:28:19,555 They have a shorter route to the cortex, 452 00:28:19,555 --> 00:28:22,540 so the geniculate body evolved. 453 00:28:22,540 --> 00:28:26,070 Be that as it may be, the next structure, then, 454 00:28:26,070 --> 00:28:31,235 is the pretectal area, and then finally, superior colliculus. 455 00:28:31,235 --> 00:28:34,770 Or optic tectum, but for mammals, we usually 456 00:28:34,770 --> 00:28:36,450 use the term superior colliculus. 457 00:28:39,450 --> 00:28:42,510 Let's look at the geniculate body now. 458 00:28:42,510 --> 00:28:47,730 We look at animals with this kind of layer, but even more. 459 00:28:47,730 --> 00:28:50,610 Here's the geniculate body of a monkey. 460 00:28:50,610 --> 00:29:00,400 It's similar to a color picture I took from David Hubel 461 00:29:00,400 --> 00:29:05,170 from a book that he has online that anybody can download. 462 00:29:05,170 --> 00:29:06,770 Very nice book. 463 00:29:06,770 --> 00:29:10,850 Unfortunately, David died just recently, 464 00:29:10,850 --> 00:29:15,790 but he was very productive visual neuroscientist 465 00:29:15,790 --> 00:29:22,190 who did many studies of both cat and monkey geniculate striate 466 00:29:22,190 --> 00:29:27,520 system, looking mostly in the visual cortex. 467 00:29:27,520 --> 00:29:29,020 He did the work with Torsten Wiesel, 468 00:29:29,020 --> 00:29:34,480 who retired now but has had a position at Rockefeller 469 00:29:34,480 --> 00:29:39,020 University for the last quite a few years 470 00:29:39,020 --> 00:29:42,900 after he left Harvard from his work with Hubel. 471 00:29:42,900 --> 00:29:46,320 Here, it shows you how the number-- oh 472 00:29:46,320 --> 00:29:49,135 yeah, where did this horseshoe shape come from? 473 00:29:49,135 --> 00:29:50,510 That's not what I'm showing here. 474 00:29:57,864 --> 00:30:00,740 Can you figure that out? 475 00:30:00,740 --> 00:30:02,015 Let's go back to the embryo. 476 00:30:02,015 --> 00:30:05,030 It looked like this. 477 00:30:05,030 --> 00:30:07,620 Monkey is the same. 478 00:30:07,620 --> 00:30:11,260 This structure here grew and grew and grew, 479 00:30:11,260 --> 00:30:16,340 so this structure got pushed this way. 480 00:30:23,460 --> 00:30:29,460 The pulvinar, in growing so big, the thalamus 481 00:30:29,460 --> 00:30:33,050 in front of it also grew and so this thing 482 00:30:33,050 --> 00:30:35,910 that's on the side of the thalamus here, 483 00:30:35,910 --> 00:30:41,040 side of the thalamus got pushed over like that and also got 484 00:30:41,040 --> 00:30:43,510 rotated so the geniculate body ends up 485 00:30:43,510 --> 00:30:46,640 on the back of the thalamus. 486 00:30:46,640 --> 00:30:52,590 It goes that way and this becomes like that. 487 00:30:52,590 --> 00:30:56,760 And the optic tract, which was out here, is now under here. 488 00:31:00,110 --> 00:31:05,420 That means this is the optic tract surface. 489 00:31:09,130 --> 00:31:09,970 Those are the axons. 490 00:31:09,970 --> 00:31:13,330 The tissue is thrown off here. 491 00:31:13,330 --> 00:31:14,830 But that's where the optic tract is. 492 00:31:17,880 --> 00:31:22,170 Topologically, it's the same as this picture here. 493 00:31:29,970 --> 00:31:32,190 You see the way they number them-- they always 494 00:31:32,190 --> 00:31:36,690 start numbering them nearest the optic tract. 495 00:31:36,690 --> 00:31:39,920 One, two, notice the first two layers 496 00:31:39,920 --> 00:31:43,920 are larger cells and then the smaller cell 497 00:31:43,920 --> 00:31:47,100 layers, or parval cellular layers, 498 00:31:47,100 --> 00:31:48,540 are three, four, five, and six. 499 00:31:52,570 --> 00:31:54,690 Again, you have half of them that 500 00:31:54,690 --> 00:31:59,153 are contralateral input and the other half 501 00:31:59,153 --> 00:32:00,310 are getting ipsilateral. 502 00:32:00,310 --> 00:32:04,850 Almost always, the contralateral is projecting to surface layer 503 00:32:04,850 --> 00:32:11,640 and to the last layer here and to one of these middle layers. 504 00:32:11,640 --> 00:32:14,190 It varies a little bit among species. 505 00:32:14,190 --> 00:32:16,600 Here's a human. 506 00:32:16,600 --> 00:32:21,950 This is a human, a picture that was donated 507 00:32:21,950 --> 00:32:25,170 to me by a former student who developed a silver stain 508 00:32:25,170 --> 00:32:27,270 that stains cell bodies. 509 00:32:27,270 --> 00:32:29,890 It gives you a very high contrast picture. 510 00:32:29,890 --> 00:32:34,240 This happens to be from a human case who had a pathology of one 511 00:32:34,240 --> 00:32:42,010 eye, so the cells of the of the eye that 512 00:32:42,010 --> 00:32:47,230 gets ipsilateral projections, the cells have shriveled a bit. 513 00:32:47,230 --> 00:32:50,870 This is one of the magnocellular layers here, 514 00:32:50,870 --> 00:32:53,110 and here's the other contralateral layer 515 00:32:53,110 --> 00:32:55,630 and the last contralateral layers. 516 00:32:55,630 --> 00:32:59,810 These are the layers getting ipsilateral projections. 517 00:32:59,810 --> 00:33:04,380 Most of the other magnocellular layer, we don't see here. 518 00:33:04,380 --> 00:33:08,190 All of these cells here are all parts 519 00:33:08,190 --> 00:33:13,190 of that lateral thalamus, the pulvinar nucleus. 520 00:33:13,190 --> 00:33:14,690 There's a small part of it that they 521 00:33:14,690 --> 00:33:19,280 call-- the part that's inferior pulvinar-- 522 00:33:19,280 --> 00:33:23,410 it's similar to LP of the rodent. 523 00:33:23,410 --> 00:33:26,060 Often they do name an LP, too, but the homology 524 00:33:26,060 --> 00:33:30,440 is not always that clear. 525 00:33:30,440 --> 00:33:35,620 This is a picture from a very famous neuroanatomist 526 00:33:35,620 --> 00:33:40,430 in the early part of the 20th century, Le Gros Clark, 527 00:33:40,430 --> 00:33:47,640 who didn't have access to beautiful optics for taking 528 00:33:47,640 --> 00:33:50,610 low-power pictures and all that, so he drew them. 529 00:33:50,610 --> 00:33:52,870 He drew these beautiful pictures, 530 00:33:52,870 --> 00:33:57,910 in this case of many different primates. 531 00:33:57,910 --> 00:34:01,290 At that time, they thought the treeshrew 532 00:34:01,290 --> 00:34:03,740 might be the most primitive primate. 533 00:34:03,740 --> 00:34:07,660 It turns out to be similar to very primitive primates, 534 00:34:07,660 --> 00:34:11,239 but it's actually an insectovore. 535 00:34:11,239 --> 00:34:14,830 You see the different patterns of lamination 536 00:34:14,830 --> 00:34:18,219 that occur in these different animals. 537 00:34:18,219 --> 00:34:21,200 They don't all have identical structures. 538 00:34:23,969 --> 00:34:29,440 Binocular separation-- the anatomy underlying 539 00:34:29,440 --> 00:34:31,920 that binocular separation of the brain 540 00:34:31,920 --> 00:34:34,511 has evolved differently in different animals. 541 00:34:38,360 --> 00:34:43,420 In these pictures, the old world monkey, the guenon, 542 00:34:43,420 --> 00:34:44,850 is most similar to the human. 543 00:34:52,580 --> 00:34:56,050 This picture here is fairly close and level 544 00:34:56,050 --> 00:35:00,160 to that picture of the photograph. 545 00:35:00,160 --> 00:35:03,240 Now I want to go to the rodent, which are usually 546 00:35:03,240 --> 00:35:09,265 used in laboratory work-- a lot of the studies of many systems. 547 00:35:15,880 --> 00:35:18,720 I use side views and I show-- here's 548 00:35:18,720 --> 00:35:21,220 a very simplified picture of it. 549 00:35:21,220 --> 00:35:26,470 The outline here is a fairly accurate view, a side view, 550 00:35:26,470 --> 00:35:30,050 of the upper brainstem of a hamster. 551 00:35:30,050 --> 00:35:32,510 You see the inferior colliculus and super colliculus 552 00:35:32,510 --> 00:35:35,300 of the midbrain here. 553 00:35:35,300 --> 00:35:36,445 This is our thalamus. 554 00:35:41,300 --> 00:35:43,970 The dorsal thalamus would be all through here, 555 00:35:43,970 --> 00:35:48,650 but the geniculate body here, way out at the edge, 556 00:35:48,650 --> 00:35:54,280 here's the two parts-- dorsal and dentral nuclei. 557 00:35:54,280 --> 00:35:57,760 Remember, I said that the ventral nucleus 558 00:35:57,760 --> 00:36:01,820 and lateral geniculate is really subthalamus. 559 00:36:01,820 --> 00:36:03,400 Remember, it's a curved structure, 560 00:36:03,400 --> 00:36:07,650 so this is at the lateral edge so it's much higher up. 561 00:36:07,650 --> 00:36:09,347 As we went deeper into the thalamus, 562 00:36:09,347 --> 00:36:10,430 it would be way down here. 563 00:36:14,060 --> 00:36:17,170 What I show here is a little schematic 564 00:36:17,170 --> 00:36:21,370 of one little bundle of optic tract axons coming 565 00:36:21,370 --> 00:36:23,040 from the chiasm up the side. 566 00:36:23,040 --> 00:36:27,440 I don't show the terminations in the suprachiasmatic nucleus 567 00:36:27,440 --> 00:36:30,140 because those are different axons, 568 00:36:30,140 --> 00:36:34,000 but I show that axons that go to the geniculate body 569 00:36:34,000 --> 00:36:38,131 are usually branches of optic tract axons that go further. 570 00:36:38,131 --> 00:36:41,410 They go to the tectum, and often the pretectum, as well. 571 00:36:43,960 --> 00:36:47,460 I also show where the major input 572 00:36:47,460 --> 00:36:51,280 to the LP that provides the LP with visual information 573 00:36:51,280 --> 00:36:53,820 doesn't come from the retina even though there 574 00:36:53,820 --> 00:36:55,620 are a few projections there. 575 00:36:55,620 --> 00:36:59,600 They come from the superficial or visual layers 576 00:36:59,600 --> 00:37:01,360 of the superior colliculus. 577 00:37:01,360 --> 00:37:05,310 It projects to both the LP and to the outer layer 578 00:37:05,310 --> 00:37:09,300 of the ventral nucleus of the lateral geniculate body. 579 00:37:15,840 --> 00:37:19,850 Here's the question that I want to answer next-- 580 00:37:19,850 --> 00:37:22,695 there are axons that leave the main optic tract 581 00:37:22,695 --> 00:37:25,490 and terminate in the small groups. 582 00:37:25,490 --> 00:37:28,910 There's up to three of them. 583 00:37:28,910 --> 00:37:32,960 They're described as what kind of optic tract? 584 00:37:32,960 --> 00:37:37,370 The word is accessory optic tract. 585 00:37:37,370 --> 00:37:43,860 This is an anatomical reconstruction of the hamster 586 00:37:43,860 --> 00:37:51,582 where I have labeled the axons, all of the axons that I could, 587 00:37:51,582 --> 00:37:54,720 which is most of them. 588 00:37:54,720 --> 00:37:58,700 I get the entire optic tract. 589 00:37:58,700 --> 00:38:00,900 This is done from serial sections, 590 00:38:00,900 --> 00:38:03,495 so the sections were actually like this 591 00:38:03,495 --> 00:38:06,980 but pretty close together. 592 00:38:06,980 --> 00:38:14,852 I then reconstructed the entire optic tract from chiasm 593 00:38:14,852 --> 00:38:17,780 to colliculus. 594 00:38:17,780 --> 00:38:24,380 In this particular brain, I was using stains for degeneration. 595 00:38:24,380 --> 00:38:27,460 I didn't get a good picture of the suprachiasmatic nucleus, 596 00:38:27,460 --> 00:38:30,570 so like most scientists, I never lie 597 00:38:30,570 --> 00:38:34,270 with the data I present-- I don't show it. 598 00:38:34,270 --> 00:38:37,167 But in fact, with other techniques, I could see it, 599 00:38:37,167 --> 00:38:38,000 and it's right here. 600 00:38:41,910 --> 00:38:45,800 What I'm showing here is the accessory optic tract axons, 601 00:38:45,800 --> 00:38:48,930 and you can see why they're called accessory optic tract. 602 00:38:48,930 --> 00:38:52,730 They need that main track that goes all the way from chiasm 603 00:38:52,730 --> 00:38:54,640 to colliculus here. 604 00:38:54,640 --> 00:38:58,580 Here are some that leave just below the cerebral peduncle 605 00:38:58,580 --> 00:39:00,500 and they travel caudally and they 606 00:39:00,500 --> 00:39:05,330 terminate medial to the peduncle, right there where 607 00:39:05,330 --> 00:39:10,500 the nucleus sort of hugs the medial side of the substantia 608 00:39:10,500 --> 00:39:12,680 nigra in the cerebral peduncle. 609 00:39:12,680 --> 00:39:18,860 Others just travel caudally below the thalamus here. 610 00:39:18,860 --> 00:39:22,260 They just sort of peel off at the level 611 00:39:22,260 --> 00:39:25,110 of the ventral lateral geniculate body. 612 00:39:25,110 --> 00:39:28,350 They terminate in a little nucleus here. 613 00:39:28,350 --> 00:39:33,450 Some axons go down this way and get to this other one. 614 00:39:33,450 --> 00:39:36,500 There's even some axons growing in another direction. 615 00:39:36,500 --> 00:39:39,590 That's called the transpeduncular tract. 616 00:39:39,590 --> 00:39:43,170 Finally, here's a little tract that 617 00:39:43,170 --> 00:39:45,750 goes from the pretectal area. 618 00:39:45,750 --> 00:39:49,844 It leaves the main tract, seems to go down 619 00:39:49,844 --> 00:39:51,260 to the lateral [? termonucleus, ?] 620 00:39:51,260 --> 00:39:53,350 but it has another little nucleus 621 00:39:53,350 --> 00:39:59,140 there way out at the lateral edge of the pretectal area. 622 00:39:59,140 --> 00:40:02,005 That's the accessory optic tract-- a very interesting 623 00:40:02,005 --> 00:40:05,680 system because all the cells in that tract 624 00:40:05,680 --> 00:40:11,470 respond to movement of the whole scene across the retina. 625 00:40:11,470 --> 00:40:13,770 No matter where you are in the retina, 626 00:40:13,770 --> 00:40:17,940 the cells will detect movement in the same direction. 627 00:40:17,940 --> 00:40:19,960 When does that happen? 628 00:40:19,960 --> 00:40:23,620 When the whole animal starts to fall? 629 00:40:23,620 --> 00:40:26,070 It happens when the animal is locomoting 630 00:40:26,070 --> 00:40:29,410 and so there's straining of the virtual world past his eyes. 631 00:40:38,040 --> 00:40:39,660 It does the same kind of functions 632 00:40:39,660 --> 00:40:43,010 that the vestibular system does. 633 00:40:43,010 --> 00:40:48,180 It gives visual signals to indicate changes 634 00:40:48,180 --> 00:40:50,320 in head direction and eye direction. 635 00:40:52,850 --> 00:40:59,920 Very important for locomotion and very important 636 00:40:59,920 --> 00:41:02,603 if you need to keep track of head position. 637 00:41:05,810 --> 00:41:11,480 Then I just want to show you what that reconstruction is 638 00:41:11,480 --> 00:41:15,630 doing by taking photographs of a similar brain. 639 00:41:15,630 --> 00:41:17,000 Here, I didn't label it. 640 00:41:17,000 --> 00:41:19,770 Here, I did. 641 00:41:19,770 --> 00:41:24,770 Here, because of the way I've shaped the light, 642 00:41:24,770 --> 00:41:28,190 you can see major tracts because they're wider. 643 00:41:28,190 --> 00:41:30,040 That's the lateral olfactory tract. 644 00:41:30,040 --> 00:41:32,950 There's the optic tract. 645 00:41:32,950 --> 00:41:36,765 There is a pathway carrying auditory input from hindbrain 646 00:41:36,765 --> 00:41:38,015 up to the inferior colliculus. 647 00:41:41,610 --> 00:41:45,330 There's the bundle-- you see these two bundles here? 648 00:41:45,330 --> 00:41:48,110 We cut those when we remove the cerebellum. 649 00:41:48,110 --> 00:41:49,640 Those are the cerebellar peduncles. 650 00:41:53,340 --> 00:41:55,570 There's hypothalamus down below. 651 00:41:58,940 --> 00:42:03,600 When I removed the brain, I tore the pituitary off right there. 652 00:42:03,600 --> 00:42:05,140 That would be the mammillary bodies 653 00:42:05,140 --> 00:42:07,980 at the caudal end of a hypothalamus. 654 00:42:07,980 --> 00:42:14,170 Here, I've labeled them and I've labeled a few other structures. 655 00:42:14,170 --> 00:42:19,130 This structure here is not thalamus, 656 00:42:19,130 --> 00:42:23,750 it's part of the endbrain-- it's the corpus striatum. 657 00:42:23,750 --> 00:42:28,247 I show you exactly where the geniculate body is. 658 00:42:28,247 --> 00:42:30,080 Now you say, well, what do you mean exactly? 659 00:42:30,080 --> 00:42:32,035 Because I can see the shadows there. 660 00:42:32,035 --> 00:42:34,320 I can see them there. 661 00:42:34,320 --> 00:42:37,955 I know that that's exactly the edge of the dorsal nucleus, 662 00:42:37,955 --> 00:42:42,320 and this is the ventral nucleus right below it. 663 00:42:42,320 --> 00:42:44,735 There's the optic tract, hypothalamus. 664 00:42:48,330 --> 00:42:51,450 This big bundle here that emerges 665 00:42:51,450 --> 00:42:54,620 from behind the optic tract-- those 666 00:42:54,620 --> 00:42:59,580 axons coursing through the corpus striatum here, 667 00:42:59,580 --> 00:43:03,610 but in the rodent, they're all separated. 668 00:43:03,610 --> 00:43:05,560 There's a bunch of little separate bundles 669 00:43:05,560 --> 00:43:07,300 that collect and form the peduncle. 670 00:43:07,300 --> 00:43:10,440 It comes along the side of the diencephalon 671 00:43:10,440 --> 00:43:16,200 and passes right on into the Pontine region here. 672 00:43:16,200 --> 00:43:17,620 When we study the auditory system, 673 00:43:17,620 --> 00:43:21,120 we'll learn that this is called the lateral lemniscus. 674 00:43:21,120 --> 00:43:25,590 That bump right there behind the cerebellar peduncles, 675 00:43:25,590 --> 00:43:27,560 that's the cochlear nucleus. 676 00:43:27,560 --> 00:43:30,227 There's the stump of the eighth node right there. 677 00:43:33,630 --> 00:43:39,680 One way to learn this stuff is to study reconstructions 678 00:43:39,680 --> 00:43:42,430 like this, look at these photographs 679 00:43:42,430 --> 00:43:45,650 and try to learn to pick out the structures. 680 00:43:45,650 --> 00:43:48,750 Right now, this is midbrain-- you 681 00:43:48,750 --> 00:43:51,482 should know what the colliculi are. 682 00:43:51,482 --> 00:43:53,690 You should know the optic tract and the hypothalamus. 683 00:43:57,190 --> 00:43:59,165 Here, if I've already told you, I've 684 00:43:59,165 --> 00:44:01,050 removed the hemispheres and the cerebellum. 685 00:44:03,830 --> 00:44:05,720 This has got to be [INAUDIBLE] hemispheres, 686 00:44:05,720 --> 00:44:07,140 and there's only one big structure 687 00:44:07,140 --> 00:44:08,514 like that-- it's corpus striatum. 688 00:44:11,760 --> 00:44:20,760 One way is to cover those up and in the book, 689 00:44:20,760 --> 00:44:24,820 it's done so you can just put a piece of paper 690 00:44:24,820 --> 00:44:28,670 and still see the lines for the labels. 691 00:44:28,670 --> 00:44:31,090 I want you to do that in your book. 692 00:44:31,090 --> 00:44:35,310 Cover up the labels and see if you can learn them. 693 00:44:35,310 --> 00:44:38,304 Learn what these structures are on this kind of picture. 694 00:44:41,150 --> 00:44:43,680 This kind of picture and this kind of reconstruction 695 00:44:43,680 --> 00:44:45,810 were very important to me for a lot 696 00:44:45,810 --> 00:44:50,700 of experiments I did because I needed to do neurosurgery 697 00:44:50,700 --> 00:44:52,180 where I would open up the brain. 698 00:44:52,180 --> 00:44:55,620 Of course, I would only see a small part, 699 00:44:55,620 --> 00:44:59,040 but I learned the landmarks so well that I could open it up 700 00:44:59,040 --> 00:45:02,910 and also using blood vessels, I could see these structures 701 00:45:02,910 --> 00:45:06,940 and see the boundaries, that way I could make injections or even 702 00:45:06,940 --> 00:45:09,300 lesions in small regions. 703 00:45:12,670 --> 00:45:15,380 This is another, somewhat easier view 704 00:45:15,380 --> 00:45:17,830 where I have the adult brain on the left 705 00:45:17,830 --> 00:45:20,630 and the brain of a newborn on the right. 706 00:45:20,630 --> 00:45:25,754 Here, I just labelled major parts of the brain-- 707 00:45:25,754 --> 00:45:31,790 the olfactory bulb, neocortex the superior colliculi, 708 00:45:31,790 --> 00:45:35,732 inferior colliculi, the cerebellum, 709 00:45:35,732 --> 00:45:40,165 and the medulla oblongata, the caudal part of the hindbrain. 710 00:45:40,165 --> 00:45:41,790 The [? lateral ?] part of the hindbrain 711 00:45:41,790 --> 00:45:43,789 is underneath the cerebellum, and the cerebellum 712 00:45:43,789 --> 00:45:45,090 is part of it. 713 00:45:45,090 --> 00:45:48,760 What I want you to know here-- look at the cerebellum 714 00:45:48,760 --> 00:45:50,590 here in the baby. 715 00:45:50,590 --> 00:45:52,410 There's just this tiny little collar 716 00:45:52,410 --> 00:45:54,870 behind the inferior colliculus. 717 00:45:54,870 --> 00:46:00,830 It's mainly developing with huge numbers of cell migrations 718 00:46:00,830 --> 00:46:02,990 from rhombic lip of the hindbrain-- 719 00:46:02,990 --> 00:46:06,980 just developing in the newborn hamster. 720 00:46:06,980 --> 00:46:11,265 It's born, remember, at a stage where it's like 721 00:46:11,265 --> 00:46:14,700 a two-and-a-half- to three-month human fetus, 722 00:46:14,700 --> 00:46:17,780 which means that a two-and-a-half month human 723 00:46:17,780 --> 00:46:22,155 fetus looks just like this, too. 724 00:46:22,155 --> 00:46:27,500 The cerebellum grows mostly after that time. 725 00:46:27,500 --> 00:46:34,550 One way to study that-- use the book and make yourself a card 726 00:46:34,550 --> 00:46:36,440 and cover those up and make sure you 727 00:46:36,440 --> 00:46:40,090 know what all those pointers are pointing towards. 728 00:46:40,090 --> 00:46:42,120 This one should be the easiest, this one 729 00:46:42,120 --> 00:46:43,120 will be a little harder. 730 00:46:52,550 --> 00:46:53,945 Can somebody tell me what E is? 731 00:46:57,270 --> 00:46:58,860 Optic tract. 732 00:46:58,860 --> 00:47:02,249 What about D? 733 00:47:02,249 --> 00:47:02,790 Hypothalamus. 734 00:47:05,730 --> 00:47:07,156 Did anybody do C? 735 00:47:07,156 --> 00:47:08,072 AUDIENCE: [INAUDIBLE]. 736 00:47:11,690 --> 00:47:13,890 PROFESSOR: Head, right. 737 00:47:13,890 --> 00:47:14,680 Cerebral peduncle. 738 00:47:20,430 --> 00:47:24,210 The abbreviation for cerebral peduncle is PED. 739 00:47:24,210 --> 00:47:26,950 I didn't label the pons, but this 740 00:47:26,950 --> 00:47:29,750 would be the pons right there. 741 00:47:29,750 --> 00:47:33,320 This is the trapezoid body, which I don't name, 742 00:47:33,320 --> 00:47:36,940 cochlear nucleus, cerebellar peduncles. 743 00:47:40,530 --> 00:47:41,900 Lateral lemniscus. 744 00:47:41,900 --> 00:47:45,920 I just labelled the ones here that-- 745 00:47:45,920 --> 00:47:47,980 we might put a diagram like this. 746 00:47:47,980 --> 00:47:49,710 We wouldn't put all those things, 747 00:47:49,710 --> 00:47:53,890 but we might ask you to do a-- give you a bunch of terms 748 00:47:53,890 --> 00:47:58,015 and say, well, which one goes with each of these letters? 749 00:47:58,015 --> 00:47:59,640 So if you're at least familiar with it, 750 00:47:59,640 --> 00:48:00,848 you would be able to do that. 751 00:48:04,790 --> 00:48:06,120 Here, the same thing. 752 00:48:06,120 --> 00:48:07,070 Here, I've covered up. 753 00:48:09,737 --> 00:48:10,820 Just name them out for me. 754 00:48:10,820 --> 00:48:11,510 What's that? 755 00:48:11,510 --> 00:48:14,000 AUDIENCE: [INAUDIBLE]. 756 00:48:14,000 --> 00:48:15,896 PROFESSOR: What's this? 757 00:48:15,896 --> 00:48:17,877 AUDIENCE: [INAUDIBLE]. 758 00:48:17,877 --> 00:48:19,460 PROFESSOR: OK, or cerebral hemisphere. 759 00:48:19,460 --> 00:48:21,300 Either one would be proper. 760 00:48:21,300 --> 00:48:22,426 What's that? 761 00:48:22,426 --> 00:48:24,010 AUDIENCE: [INAUDIBLE]. 762 00:48:24,010 --> 00:48:24,640 PROFESSOR: OK. 763 00:48:24,640 --> 00:48:27,470 Notice most of it is exposed here. 764 00:48:27,470 --> 00:48:30,140 Here only part of it is exposed. 765 00:48:30,140 --> 00:48:34,250 In most animals with even bigger hemispheres, 766 00:48:34,250 --> 00:48:38,130 you don't even see the membrane from a dorsal view like that. 767 00:48:38,130 --> 00:48:39,580 OK, and this one? 768 00:48:39,580 --> 00:48:40,840 AUDIENCE: Cerebellum. 769 00:48:40,840 --> 00:48:42,420 PROFESSOR: Cerebellum. 770 00:48:42,420 --> 00:48:42,920 This? 771 00:48:45,137 --> 00:48:46,720 Caudal hindbrain or medulla oblongata. 772 00:49:01,140 --> 00:49:03,770 I'm asking you another question here 773 00:49:03,770 --> 00:49:06,020 about naming these structures. 774 00:49:06,020 --> 00:49:07,650 I said, what would make this more 775 00:49:07,650 --> 00:49:09,494 difficult during a neurosurgical procedure? 776 00:49:12,460 --> 00:49:15,160 Think about it. 777 00:49:15,160 --> 00:49:16,940 In a neurosurgical procedure, you 778 00:49:16,940 --> 00:49:22,500 don't expose such huge amount of brain. 779 00:49:22,500 --> 00:49:26,300 You want to make as small window as possible 780 00:49:26,300 --> 00:49:31,270 so you don't damage so much tissue. 781 00:49:31,270 --> 00:49:32,630 That's the first problem. 782 00:49:35,190 --> 00:49:39,330 The second thing is there's a lot of blood vessels. 783 00:49:39,330 --> 00:49:40,890 In fact, you have to be very careful 784 00:49:40,890 --> 00:49:43,890 not to go through any really big ones 785 00:49:43,890 --> 00:49:47,000 because you'll get so much bleeding that you'll 786 00:49:47,000 --> 00:49:49,660 be spending all your time stopping the bleeding, 787 00:49:49,660 --> 00:49:54,630 and you do spend a lot of time doing that in neurosurgery, 788 00:49:54,630 --> 00:49:56,400 although now we have a method to apply 789 00:49:56,400 --> 00:50:01,010 that does stop the bleeding of all those smaller vessels, just 790 00:50:01,010 --> 00:50:01,760 not the huge ones. 791 00:50:07,450 --> 00:50:11,110 Look at these other pictures for next time 792 00:50:11,110 --> 00:50:16,570 and just see if you can figure out what's exposed. 793 00:50:16,570 --> 00:50:20,480 I use different lighting. 794 00:50:20,480 --> 00:50:25,880 This is the same kind of brain stem that you see here 795 00:50:25,880 --> 00:50:29,860 with the hemispheres removed. 796 00:50:29,860 --> 00:50:31,630 You can see various structures. 797 00:50:31,630 --> 00:50:35,310 Here I've done a little more removal up front here. 798 00:50:35,310 --> 00:50:37,472 See if you can figure out what those things are. 799 00:50:37,472 --> 00:50:39,340 I do name lot of them in the book. 800 00:50:39,340 --> 00:50:43,050 I don't think I show all these pictures in the book. 801 00:50:43,050 --> 00:50:47,370 I wanted you to see how if you adjust the light a little bit, 802 00:50:47,370 --> 00:50:49,390 you can actually see boundaries. 803 00:50:49,390 --> 00:50:51,330 Look at this one. 804 00:50:51,330 --> 00:50:54,120 There's the superior colliculus. 805 00:50:54,120 --> 00:50:55,590 There's the pretectem. 806 00:50:55,590 --> 00:50:58,620 Look at this one, even clearer. 807 00:50:58,620 --> 00:51:01,440 There's the boundary between the superior colliculus 808 00:51:01,440 --> 00:51:02,190 and pretectum. 809 00:51:02,190 --> 00:51:05,180 Look at how clear this boundary is. 810 00:51:05,180 --> 00:51:05,780 And this one. 811 00:51:08,951 --> 00:51:13,810 Pretectal area, LLP, geniculate body. 812 00:51:17,590 --> 00:51:21,370 That is the bundle carrying information 813 00:51:21,370 --> 00:51:23,645 from the amygdala, which we will study soon. 814 00:51:26,560 --> 00:51:30,100 This just shows what it looks like in the embryo when 815 00:51:30,100 --> 00:51:33,190 the axons have first grown back to the tectum-- 816 00:51:33,190 --> 00:51:36,522 a very straight pathway back to the tectum. 817 00:51:44,420 --> 00:51:47,190 Next time, we will start in this area 818 00:51:47,190 --> 00:51:49,600 and talk about the midbrain a little more, 819 00:51:49,600 --> 00:51:51,310 just look at these pictures. 820 00:51:51,310 --> 00:51:53,580 They're in the book. 821 00:51:53,580 --> 00:51:56,490 I'll give you a chance to ask about them, 822 00:51:56,490 --> 00:51:59,300 and we'll go through some of these 823 00:51:59,300 --> 00:52:02,060 before we go on to the endbrain.