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 --> 00:00:17,241 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:17,241 --> 00:00:17,866 at ocw.mit.edu. 8 00:00:22,580 --> 00:00:27,740 PROFESSOR: This is the first class since the midterm, 9 00:00:27,740 --> 00:00:37,070 but the chemical senses I want you just to read. 10 00:00:37,070 --> 00:00:40,440 And I posted questions, I hope. 11 00:00:40,440 --> 00:00:42,200 I think I remember posting some questions. 12 00:00:52,780 --> 00:00:56,310 My plan is not to give a quiz today 13 00:00:56,310 --> 00:01:00,640 and to come up with some homework. 14 00:01:00,640 --> 00:01:02,380 I think I should include something 15 00:01:02,380 --> 00:01:07,456 on chemical senses, particularly the olfactory system, 16 00:01:07,456 --> 00:01:10,980 but I hadn't settled on exactly what to do yet. 17 00:01:10,980 --> 00:01:14,645 So I'll get that done tonight or tomorrow. 18 00:01:17,890 --> 00:01:20,480 Because I'd like to spend the next three 19 00:01:20,480 --> 00:01:23,350 classes on the visual system, and then 20 00:01:23,350 --> 00:01:25,390 two classes on the auditory system. 21 00:01:33,810 --> 00:01:36,430 If you bring your books to the class, 22 00:01:36,430 --> 00:01:38,750 I guess it's a little heavy to lug around, 23 00:01:38,750 --> 00:01:43,790 but I want to give you-- unfortunately, 24 00:01:43,790 --> 00:01:51,470 I've found small errors, one just a typo, 25 00:01:51,470 --> 00:01:56,470 in the auditory system chapter. 26 00:01:56,470 --> 00:01:59,070 It's a long chapter, so that's why we need two classes. 27 00:01:59,070 --> 00:02:04,530 So I'll specify those to you. 28 00:02:04,530 --> 00:02:08,389 It's inevitable, they told me, at the MIT press, 29 00:02:08,389 --> 00:02:10,520 that when you publish a book this big, 30 00:02:10,520 --> 00:02:13,730 there's always a few things like that that you find out. 31 00:02:13,730 --> 00:02:18,745 So they will fix them in the next printing if there is one. 32 00:02:18,745 --> 00:02:19,900 I hope there will be. 33 00:02:31,890 --> 00:02:35,540 So where are we now in the outline of this class? 34 00:02:35,540 --> 00:02:43,090 We've already done seven parts, ending with the brain 35 00:02:43,090 --> 00:02:48,040 states, which is the only part with only one chapter. 36 00:02:48,040 --> 00:02:57,260 And so now with sensory systems, readings only for gustatory 37 00:02:57,260 --> 00:03:02,260 and olfactory, and now three classes on the visual systems. 38 00:03:05,000 --> 00:03:08,270 And notice I used that in the plural, 39 00:03:08,270 --> 00:03:13,540 because there's multiple systems for vision. 40 00:03:13,540 --> 00:03:18,800 Some of them operate pretty much independent of the others. 41 00:03:18,800 --> 00:03:20,000 So we'll start that today. 42 00:03:23,102 --> 00:03:25,720 We'll start with a little bit on the origins of vision, 43 00:03:25,720 --> 00:03:27,920 with light detection. 44 00:03:27,920 --> 00:03:30,525 And then finally, image formation 45 00:03:30,525 --> 00:03:34,130 and the major functions it serves-- predatory escape, 46 00:03:34,130 --> 00:03:37,020 which we've been talking about before, orienting 47 00:03:37,020 --> 00:03:39,400 towards objects, and then identifying 48 00:03:39,400 --> 00:03:42,990 patterns and objects and individuals. 49 00:03:46,702 --> 00:03:48,160 And then I want to start going over 50 00:03:48,160 --> 00:03:50,840 the retinal projections in more detail. 51 00:03:50,840 --> 00:03:55,580 And next time, we'll look at that in a different way 52 00:03:55,580 --> 00:03:57,126 in a little more detail, because I'd 53 00:03:57,126 --> 00:03:59,000 like you to be able to remember some of that. 54 00:04:02,090 --> 00:04:04,480 You guys have pretty good memories. 55 00:04:04,480 --> 00:04:07,000 Just a little aside here-- I was pleased 56 00:04:07,000 --> 00:04:10,326 with the results of the midterm. 57 00:04:10,326 --> 00:04:16,100 You figure that 85 to 100 is an A, there were a lot of As. 58 00:04:16,100 --> 00:04:19,089 And Bs go all the way down to 70, 59 00:04:19,089 --> 00:04:24,000 so that means nobody got below a B. All As and Bs. 60 00:04:24,000 --> 00:04:28,430 So I should be clapping up here for you. 61 00:04:31,330 --> 00:04:32,730 So keep it up. 62 00:04:32,730 --> 00:04:35,540 Keep working hard, and you'll all get As and Bs for sure. 63 00:04:38,180 --> 00:04:40,030 All right. 64 00:04:40,030 --> 00:04:44,627 So what in all likelihood was the first functional role 65 00:04:44,627 --> 00:04:47,620 of the visual sense? 66 00:04:47,620 --> 00:04:50,300 And I want you to be able to describe the nature of the most 67 00:04:50,300 --> 00:04:52,660 primitive projection of the eyes to the brain. 68 00:04:52,660 --> 00:04:54,660 And I point out here that it was actually 69 00:04:54,660 --> 00:04:57,470 the last of the major retinal projections to be discovered. 70 00:05:00,190 --> 00:05:02,450 Even after this one was discovered, 71 00:05:02,450 --> 00:05:06,870 there's been a few more, and I'll point some of that 72 00:05:06,870 --> 00:05:08,340 out in today's class. 73 00:05:11,520 --> 00:05:16,660 So what do I claim is the most primitive function of vision? 74 00:05:16,660 --> 00:05:20,385 It was there, even in amphioxus. 75 00:05:20,385 --> 00:05:20,884 Sorry? 76 00:05:20,884 --> 00:05:25,090 AUDIENCE: Avoidance of predators? 77 00:05:25,090 --> 00:05:27,390 PROFESSOR: Predators? 78 00:05:27,390 --> 00:05:28,860 No. 79 00:05:28,860 --> 00:05:31,650 AUDIENCE: [INAUDIBLE]. 80 00:05:31,650 --> 00:05:34,540 PROFESSOR: Well, the pineal eye is 81 00:05:34,540 --> 00:05:36,630 one of the ways this was expressed, 82 00:05:36,630 --> 00:05:39,590 that's right-- just detection of light. 83 00:05:39,590 --> 00:05:41,680 Think of the most primitive chordate 84 00:05:41,680 --> 00:05:43,520 we talked about, amphioxus. 85 00:05:43,520 --> 00:05:46,690 He doesn't have a lens. 86 00:05:46,690 --> 00:05:50,000 But he can detect light. 87 00:05:50,000 --> 00:05:52,260 I'll show you that again today. 88 00:05:52,260 --> 00:05:55,760 So we think that's got to be the most primitive sense. 89 00:05:55,760 --> 00:05:57,510 So then we look at, well, what are 90 00:05:57,510 --> 00:06:03,760 the pathways in the mammal that just do that? 91 00:06:03,760 --> 00:06:08,400 OK, so we'll look at that here, two of them. 92 00:06:08,400 --> 00:06:12,220 Why was it so important to detect light? 93 00:06:12,220 --> 00:06:16,340 It long preceded image formation and topographic projections. 94 00:06:16,340 --> 00:06:20,640 It took a long time to evolve a lens. 95 00:06:20,640 --> 00:06:23,730 And we don't know all the details of how that happened. 96 00:06:27,180 --> 00:06:31,050 So that means the only topography 97 00:06:31,050 --> 00:06:33,670 in primitive, bilaterally symmetric animals, 98 00:06:33,670 --> 00:06:36,480 the only topography was they had a light detector 99 00:06:36,480 --> 00:06:38,660 on the right and a light detector on the left. 100 00:06:38,660 --> 00:06:41,660 They could see differences in light intensity 101 00:06:41,660 --> 00:06:43,140 on the right and left sides. 102 00:06:43,140 --> 00:06:45,650 So if some animal was approaching them, 103 00:06:45,650 --> 00:06:48,260 attacking them, they might be able to detect, 104 00:06:48,260 --> 00:06:50,750 oh, there's something over there. 105 00:06:50,750 --> 00:06:54,220 So I need to go the other way. 106 00:06:54,220 --> 00:07:01,150 So we know this is just on the primitive origins 107 00:07:01,150 --> 00:07:03,135 that we've gone over before. 108 00:07:07,810 --> 00:07:11,510 It was very adaptive for organizing the night and day 109 00:07:11,510 --> 00:07:15,390 for efficiency and for safety. 110 00:07:15,390 --> 00:07:21,280 If you're a day-active animal, you 111 00:07:21,280 --> 00:07:24,380 need a place to get away from other animals at night 112 00:07:24,380 --> 00:07:25,956 in order to sleep. 113 00:07:25,956 --> 00:07:29,480 If you're a night-active animal, you 114 00:07:29,480 --> 00:07:31,420 need a place to sleep during the day. 115 00:07:31,420 --> 00:07:32,540 You're inactive. 116 00:07:32,540 --> 00:07:36,980 But then if you use vision for predation, 117 00:07:36,980 --> 00:07:40,310 you have to have vision in very low lights, 118 00:07:40,310 --> 00:07:43,460 and you're more likely to use other senses 119 00:07:43,460 --> 00:07:46,230 in addition to vision that might be even more important. 120 00:07:46,230 --> 00:07:51,080 Those would be olfactory and auditory. 121 00:07:51,080 --> 00:07:53,310 Somatosensory less so, but somatosensory 122 00:07:53,310 --> 00:07:55,580 does play an important role in predation too 123 00:07:55,580 --> 00:07:57,270 in attack behavior. 124 00:07:57,270 --> 00:08:00,380 We'll talk a little more about that later on. 125 00:08:00,380 --> 00:08:01,360 OK. 126 00:08:01,360 --> 00:08:03,020 So this is just a reminder. 127 00:08:03,020 --> 00:08:07,790 This is amphioxus, the rostralmost end of amphioxus. 128 00:08:10,450 --> 00:08:15,870 You find cells with pigment in them. 129 00:08:15,870 --> 00:08:20,330 But more importantly, right next to the pigment cells, 130 00:08:20,330 --> 00:08:27,850 there are cells that are light receptors. 131 00:08:27,850 --> 00:08:32,730 And next to them are cells that have axons that project 132 00:08:32,730 --> 00:08:36,789 to other parts of the nervous system of amphioxus. 133 00:08:36,789 --> 00:08:39,049 And you can compare the arrangement 134 00:08:39,049 --> 00:08:43,270 of cells in that light spot in amphioxus 135 00:08:43,270 --> 00:08:45,960 to the cells in the developing retina. 136 00:08:45,960 --> 00:08:48,430 Normally the retina develops as sort 137 00:08:48,430 --> 00:08:52,230 of an out-pouching of the sides of the diencephalon. 138 00:08:55,270 --> 00:08:58,746 What causes that out-pouching to occur? 139 00:08:58,746 --> 00:09:02,990 It's actually induced by things at the surface. 140 00:09:02,990 --> 00:09:05,503 Placode, in this case, the lens placode. 141 00:09:08,060 --> 00:09:13,470 And that causes the neural tube to extend out 142 00:09:13,470 --> 00:09:15,890 towards the surface. 143 00:09:15,890 --> 00:09:17,580 So here you see that. 144 00:09:17,580 --> 00:09:22,290 And you see pigmented cells and the cells 145 00:09:22,290 --> 00:09:27,060 of the central nervous system here, 146 00:09:27,060 --> 00:09:32,520 including the retinal ganglion cells, bipolar cells, 147 00:09:32,520 --> 00:09:37,630 and the visual receptor cells. 148 00:09:37,630 --> 00:09:43,450 And this moves back here, so the receptors are actually 149 00:09:43,450 --> 00:09:44,480 in the back. 150 00:09:44,480 --> 00:09:47,684 The light comes in. 151 00:09:47,684 --> 00:09:49,920 It forms a cup-like arrangement. 152 00:09:49,920 --> 00:09:52,555 The light comes in this way, goes through the receptors. 153 00:09:52,555 --> 00:09:53,900 But they're very transparent. 154 00:09:53,900 --> 00:09:56,910 They don't cause much distortion. 155 00:09:56,910 --> 00:09:58,650 Seems like a strange arrangement, 156 00:09:58,650 --> 00:09:59,900 but that's the way it evolved. 157 00:10:04,115 --> 00:10:06,005 So now this is just another representation 158 00:10:06,005 --> 00:10:09,682 of the same thing, where they compare a primitive vertebrate 159 00:10:09,682 --> 00:10:13,460 with the amphioxus. 160 00:10:13,460 --> 00:10:16,520 And I pointed out before that we know from gene expression data 161 00:10:16,520 --> 00:10:20,407 now that even amphioxus does have a hindbrain, a midbrain, 162 00:10:20,407 --> 00:10:22,480 and a forebrain, but its forebrain 163 00:10:22,480 --> 00:10:24,280 is only a diencephalon. 164 00:10:27,450 --> 00:10:27,950 OK. 165 00:10:33,480 --> 00:10:36,940 You want to behave differently in day and night. 166 00:10:36,940 --> 00:10:42,150 But what if you're spending time underground? 167 00:10:42,150 --> 00:10:46,240 Or what if the light is very dim? 168 00:10:46,240 --> 00:10:47,920 You don't get the normal signals. 169 00:10:47,920 --> 00:10:54,760 Well, it's an amazing thing that evolved that supplements that. 170 00:10:54,760 --> 00:10:58,920 You don't need just light, which can vary a lot. 171 00:10:58,920 --> 00:11:06,900 You determine your activity by an endogenous process, 172 00:11:06,900 --> 00:11:11,280 the cells that have a circadian rhythm of activity. 173 00:11:11,280 --> 00:11:14,910 But they are normally every day, they're 174 00:11:14,910 --> 00:11:17,660 affected by the light-dark cycle. 175 00:11:17,660 --> 00:11:21,440 So we say they're entrained by the light-dark cycle. 176 00:11:21,440 --> 00:11:25,650 So they oscillate at 24 hours instead of 24 hours and 20 177 00:11:25,650 --> 00:11:28,060 minutes, or 30 minutes, or whatever-- 178 00:11:28,060 --> 00:11:33,830 sometimes as long as 25 hours, including in humans, 179 00:11:33,830 --> 00:11:37,590 sometimes a little less than 24 is their natural rhythm, 180 00:11:37,590 --> 00:11:39,580 but they're all of them, no matter what 181 00:11:39,580 --> 00:11:41,190 the natural rhythm of those cells 182 00:11:41,190 --> 00:11:45,350 is, it's entrained to the light-dark cycle, normally 183 00:11:45,350 --> 00:11:47,710 the light onset. 184 00:11:47,710 --> 00:11:50,690 That's why if you have trouble-- if you're 185 00:11:50,690 --> 00:11:55,610 circadian rhythm drifting, you can mess about at MIT 186 00:11:55,610 --> 00:12:01,540 by staying up all night and not-- it can be a problem. 187 00:12:01,540 --> 00:12:07,800 And one way to help with that is to exposure yourself 188 00:12:07,800 --> 00:12:10,805 to bright light in the morning, especially sunlight, 189 00:12:10,805 --> 00:12:13,540 especially effective. 190 00:12:13,540 --> 00:12:19,240 Some people like to sleep by open windows because of that. 191 00:12:19,240 --> 00:12:20,990 And if you're an MIT student, you probably 192 00:12:20,990 --> 00:12:22,740 hate to sleep by an open window. 193 00:12:22,740 --> 00:12:24,617 You want to be able to sleep in. 194 00:12:27,750 --> 00:12:29,450 So the only thing that's been found 195 00:12:29,450 --> 00:12:33,900 that you can counter some of the problems that can cause 196 00:12:33,900 --> 00:12:39,450 is to take low doses of melatonin. 197 00:12:39,450 --> 00:12:42,375 And I'll say a little more about why 198 00:12:42,375 --> 00:12:44,354 I said low doses of melatonin. 199 00:12:49,550 --> 00:12:51,450 So light controls the daily rhythm 200 00:12:51,450 --> 00:12:53,475 of secretion of melatonin. 201 00:12:53,475 --> 00:12:55,994 It controls daily rhythm of secretion, actually, 202 00:12:55,994 --> 00:12:56,910 of a number of things. 203 00:12:59,712 --> 00:13:01,660 But one of them is melatonin. 204 00:13:01,660 --> 00:13:03,650 It's secreted by the pineal gland. 205 00:13:03,650 --> 00:13:09,630 So how does light effect that rhythm of secretion. 206 00:13:12,740 --> 00:13:16,876 You can say that, well, it's just by the endogenous rhythm. 207 00:13:16,876 --> 00:13:21,575 But actually, no, it's affected by light. 208 00:13:21,575 --> 00:13:24,330 And there's two different pathways in different animals. 209 00:13:24,330 --> 00:13:28,800 One is very ancient that you mentioned 210 00:13:28,800 --> 00:13:32,160 at the beginning of the class-- the oldest pathway 211 00:13:32,160 --> 00:13:34,940 to affect secretion of melatonin. 212 00:13:37,450 --> 00:13:38,950 What was it? 213 00:13:38,950 --> 00:13:41,510 The pineal eye. 214 00:13:41,510 --> 00:13:43,317 A number of animals have that eye. 215 00:13:43,317 --> 00:13:46,450 A number of fish have it, some amphibians have it, 216 00:13:46,450 --> 00:13:49,270 and I think even some reptiles. 217 00:13:49,270 --> 00:13:51,900 It's an eye on the top of the head, a third eye. 218 00:13:55,050 --> 00:13:56,890 It's led to all kinds of fantasies 219 00:13:56,890 --> 00:13:58,660 in science fiction, everything else, 220 00:13:58,660 --> 00:14:04,290 but all it is is a light detector that 221 00:14:04,290 --> 00:14:08,740 affects the pineal, it has close connections to the pineal. 222 00:14:08,740 --> 00:14:12,360 What about the other pathway? 223 00:14:12,360 --> 00:14:14,630 We don't have a pineal eye. 224 00:14:14,630 --> 00:14:16,860 We've got a thick skull. 225 00:14:16,860 --> 00:14:18,865 Now, if you're a mouse, the skull is thin, 226 00:14:18,865 --> 00:14:22,190 and some light can get right through that skull 227 00:14:22,190 --> 00:14:23,800 and affect the pineal. 228 00:14:23,800 --> 00:14:25,320 And yes, there are cells that are 229 00:14:25,320 --> 00:14:28,460 sensitive to that light coming right through the skull. 230 00:14:28,460 --> 00:14:32,180 But a lot of vertebrates have a thicker skull, like us. 231 00:14:32,180 --> 00:14:36,242 So even the rat's got a pretty thick skull. 232 00:14:36,242 --> 00:14:40,320 So light can't really get through-- or at least, 233 00:14:40,320 --> 00:14:42,020 very, very little. 234 00:14:42,020 --> 00:14:46,440 So let's talk about that pathway. 235 00:14:46,440 --> 00:14:50,980 But first, let me show you the mammalian suprachiasmatic 236 00:14:50,980 --> 00:14:57,860 nucleus, where the cells have this endogenous circadian 237 00:14:57,860 --> 00:14:58,360 rhythm. 238 00:14:58,360 --> 00:15:01,760 It means circa, dium-- about a day in length, 239 00:15:01,760 --> 00:15:04,390 because it varies a little bit. 240 00:15:04,390 --> 00:15:06,820 And then we'll talk about the pineal gland and melatonin 241 00:15:06,820 --> 00:15:08,390 production, the pathway. 242 00:15:08,390 --> 00:15:11,200 So this is from one of the studies 243 00:15:11,200 --> 00:15:14,810 that I did with a postdoc in my lab. 244 00:15:14,810 --> 00:15:18,860 We were using a method that's very sensitive compared 245 00:15:18,860 --> 00:15:22,200 to earlier methods for tracing pathways 246 00:15:22,200 --> 00:15:23,450 in the central nervous system. 247 00:15:23,450 --> 00:15:25,840 And here we were tracing them from the retinal ganglion 248 00:15:25,840 --> 00:15:27,190 cells. 249 00:15:27,190 --> 00:15:29,940 This is the low power picture at the bottom. 250 00:15:34,560 --> 00:15:41,450 So what it's showing here is the suprachiasmatic nucleus 251 00:15:41,450 --> 00:15:43,570 and the number of nuclei-- that's 252 00:15:43,570 --> 00:15:46,010 what SCN is, suprachiasmatic nucleus. 253 00:15:46,010 --> 00:15:49,100 But notice that it spills outside that 254 00:15:49,100 --> 00:15:51,860 and goes to these other areas around it as well. 255 00:15:51,860 --> 00:15:56,300 In fact, there's even a few axons, to our surprise, 256 00:15:56,300 --> 00:16:02,030 went all the way into the olfactory areas of cortex. 257 00:16:02,030 --> 00:16:04,365 None of that was known before these methods got 258 00:16:04,365 --> 00:16:06,610 so sensitive-- so sensitive that we could trace 259 00:16:06,610 --> 00:16:08,150 individual axons. 260 00:16:08,150 --> 00:16:12,050 They look like they were stained with the Golgi method, 261 00:16:12,050 --> 00:16:16,540 except we get them all, all the retinal ganglion cell axons. 262 00:16:16,540 --> 00:16:20,130 And then these are enlargements. 263 00:16:20,130 --> 00:16:23,240 The suprachiasmatic nucleus would be here. 264 00:16:23,240 --> 00:16:25,110 And here's a sagittal view. 265 00:16:25,110 --> 00:16:26,500 This would be suprachiasmatic. 266 00:16:26,500 --> 00:16:30,465 But you can see, they're in the anterior hypothalamic nucleus. 267 00:16:30,465 --> 00:16:33,530 They're in the nucleus right above, even 268 00:16:33,530 --> 00:16:35,950 a little bit in the ventromedial. 269 00:16:35,950 --> 00:16:38,350 If you look at this slide, it's from a rat. 270 00:16:38,350 --> 00:16:40,130 And here's the frontal section. 271 00:16:40,130 --> 00:16:42,130 This is a Nissl stain, so you see 272 00:16:42,130 --> 00:16:46,530 how clear that suprachiasmatic nucleus is. 273 00:16:46,530 --> 00:16:48,000 These are the axons down here. 274 00:16:48,000 --> 00:16:51,480 They're not stained in this, like they were here. 275 00:16:51,480 --> 00:16:54,920 These are the axons at the bottom here. 276 00:16:54,920 --> 00:16:57,010 There you'll see them in the chart 277 00:16:57,010 --> 00:17:00,020 and here in the photograph. 278 00:17:00,020 --> 00:17:02,260 So they're down here. 279 00:17:02,260 --> 00:17:05,859 So we know then, the retina projects heavily-- 280 00:17:05,859 --> 00:17:07,910 oh, one other thing I left it. 281 00:17:07,910 --> 00:17:09,720 Notice that it's going to both sides. 282 00:17:09,720 --> 00:17:13,579 I labeled the axons from only one eye. 283 00:17:13,579 --> 00:17:18,910 But they're going pretty much equally to the two sides. 284 00:17:18,910 --> 00:17:22,380 And that's true in all the animals that have been studied. 285 00:17:25,220 --> 00:17:27,420 This you don't need to pay attention to. 286 00:17:27,420 --> 00:17:34,172 It's looking at a more specific stain for a particular peptide 287 00:17:34,172 --> 00:17:35,754 that is found in some of the neurons 288 00:17:35,754 --> 00:17:37,045 of the suprachiasmatic nucleus. 289 00:17:37,045 --> 00:17:40,810 They've found that they can actually subdivide that nucleus 290 00:17:40,810 --> 00:17:43,530 into a number of different parts that 291 00:17:43,530 --> 00:17:45,440 do have slightly different projections, 292 00:17:45,440 --> 00:17:49,390 and we believe, probably different functions. 293 00:17:49,390 --> 00:17:51,774 Some of that is still not fully known. 294 00:17:55,070 --> 00:17:57,740 But look at this complicated pathway 295 00:17:57,740 --> 00:18:02,790 that influences of light on the retinal ganglion cells 296 00:18:02,790 --> 00:18:05,115 take in order to reach the pineal. 297 00:18:05,115 --> 00:18:07,450 Here they go to the suprachiasmatic, 298 00:18:07,450 --> 00:18:12,810 and short axons go from there to a more dorsally located 299 00:18:12,810 --> 00:18:16,360 hypothalamic nucleus. 300 00:18:16,360 --> 00:18:19,070 Paraventricular hypothalamic nucleus-- 301 00:18:19,070 --> 00:18:21,130 that's what PDH means. 302 00:18:21,130 --> 00:18:23,360 And there are long axon from that nucleus that 303 00:18:23,360 --> 00:18:26,850 connect to the sympathetic nervous system 304 00:18:26,850 --> 00:18:30,330 by axons that go right down to the lateral horn 305 00:18:30,330 --> 00:18:31,950 in the upper thoracic cord. 306 00:18:31,950 --> 00:18:36,770 Remember, the lateral horn cells are the preganglionic motor 307 00:18:36,770 --> 00:18:38,700 neurons of the sympathetic nervous system. 308 00:18:38,700 --> 00:18:45,110 They're found all the way from T1 down to L2 or L3. 309 00:18:45,110 --> 00:18:47,830 So they get the influence of light. 310 00:18:47,830 --> 00:18:49,710 They're activated. 311 00:18:49,710 --> 00:18:52,740 Here the axon goes out into the ganglion. 312 00:18:52,740 --> 00:18:56,885 SCG means the superior cervical ganglia. 313 00:18:56,885 --> 00:18:59,400 It's part of that chain of sympathetic ganglia 314 00:18:59,400 --> 00:19:01,390 on either side of the spinal cord. 315 00:19:01,390 --> 00:19:03,860 Superior cervical ganglia is right up here. 316 00:19:06,930 --> 00:19:10,930 It's way up in your neck. 317 00:19:10,930 --> 00:19:14,411 That's where the cervical cord is, of course, 318 00:19:14,411 --> 00:19:18,090 below the skull, uppermost spinal cord. 319 00:19:18,090 --> 00:19:21,040 And axons from the superior cervical ganglia 320 00:19:21,040 --> 00:19:26,400 provide the sympathetic innervation of the head region. 321 00:19:26,400 --> 00:19:29,200 So some of those axons-- now, remember, 322 00:19:29,200 --> 00:19:32,610 axons are going to all over from the head. 323 00:19:32,610 --> 00:19:40,370 They go to the iris of the eye, for example, 324 00:19:40,370 --> 00:19:45,820 and cause pupillary dilation with sympathetic activation. 325 00:19:45,820 --> 00:19:48,410 But this is just one pathway here 326 00:19:48,410 --> 00:19:51,790 that goes directly to the pineal gland. 327 00:19:51,790 --> 00:19:59,165 And that is how light controls the daily rhythm of secretion 328 00:19:59,165 --> 00:19:59,970 of melatonin. 329 00:20:03,481 --> 00:20:03,980 OK. 330 00:20:03,980 --> 00:20:11,370 So how about taking melatonin pills? 331 00:20:11,370 --> 00:20:15,250 It's sort of popular and all kinds of beliefs about it. 332 00:20:15,250 --> 00:20:21,835 Unfortunately, they're not produced by the drug industry. 333 00:20:21,835 --> 00:20:24,280 They're produced by various companies that 334 00:20:24,280 --> 00:20:29,000 aren't regulated by the Food and Drug Administration. 335 00:20:29,000 --> 00:20:33,315 Therefore, the government, NIH, has no say 336 00:20:33,315 --> 00:20:35,925 over what they can put in the pills. 337 00:20:35,925 --> 00:20:39,980 And people have this tendency, and I'm 338 00:20:39,980 --> 00:20:42,610 sure you've noticed it in yourself, 339 00:20:42,610 --> 00:20:46,080 that if a little bit is good, more is better. 340 00:20:46,080 --> 00:20:51,420 So people take-- they see these things on the shell, 341 00:20:51,420 --> 00:20:57,504 oh, 1 milligram of melatonin, two, three, five, 10. 342 00:20:57,504 --> 00:20:59,920 They buy the 10. 343 00:20:59,920 --> 00:21:01,100 Here's what happens. 344 00:21:01,100 --> 00:21:04,940 You take those big pills, you swamp the receptors, 345 00:21:04,940 --> 00:21:12,570 you totally saturate them, and mess up their normal secretion. 346 00:21:12,570 --> 00:21:15,430 So you can end up having more problems. 347 00:21:15,430 --> 00:21:17,070 So people aren't helping themselves, 348 00:21:17,070 --> 00:21:18,230 but they don't know it. 349 00:21:18,230 --> 00:21:21,750 They're so convinced that more is better. 350 00:21:21,750 --> 00:21:26,400 So if you want to take melatonin, 351 00:21:26,400 --> 00:21:33,528 get the 300 microgram pills, the low-dose melatonin pills. 352 00:21:36,960 --> 00:21:40,970 And I've taken them when I go on trips, 353 00:21:40,970 --> 00:21:43,650 and it helps me recover from jet lag quite rapidly. 354 00:21:43,650 --> 00:21:48,510 So if I go to China, I'm 12 hours off, 355 00:21:48,510 --> 00:21:50,930 I take the melatonin pills 20 minutes 356 00:21:50,930 --> 00:21:54,070 or 15 minutes before I go to bed. 357 00:21:54,070 --> 00:21:58,950 And within a couple days, I'm on Chinese time. 358 00:21:58,950 --> 00:22:02,050 Without that, it takes five or six days 359 00:22:02,050 --> 00:22:05,350 before I'm fully on-- and even then, 360 00:22:05,350 --> 00:22:08,640 I get sleepy at odd times. 361 00:22:08,640 --> 00:22:12,043 So that's just a bonus. 362 00:22:12,043 --> 00:22:15,880 I probably didn't put that in the book. 363 00:22:15,880 --> 00:22:16,640 I'm sure I didn't. 364 00:22:20,760 --> 00:22:22,410 I probably should. 365 00:22:22,410 --> 00:22:24,076 But not enough people will read it 366 00:22:24,076 --> 00:22:26,000 to make much of a difference. 367 00:22:26,000 --> 00:22:26,500 All right. 368 00:22:30,380 --> 00:22:33,870 Second main function of vision, of course, 369 00:22:33,870 --> 00:22:37,100 involves image formation, animals with a lens. 370 00:22:40,450 --> 00:22:43,470 And I've included the function of predator avoidance 371 00:22:43,470 --> 00:22:46,265 and escape here, even though probably before there 372 00:22:46,265 --> 00:22:49,710 were lenses, even when animals just could detect something 373 00:22:49,710 --> 00:22:52,000 different on the right and left sides of [INAUDIBLE]. 374 00:22:52,000 --> 00:22:55,160 But that's the most primitive kind of image you can get. 375 00:23:00,590 --> 00:23:04,100 It's also very useful for detecting novelty. 376 00:23:04,100 --> 00:23:06,762 If you can discriminate differences-- 377 00:23:06,762 --> 00:23:10,990 if you can use those images to see differences in patterns, 378 00:23:10,990 --> 00:23:15,100 differences in shapes, you can detect novelty. 379 00:23:15,100 --> 00:23:18,290 Novelty is critically important, because if something 380 00:23:18,290 --> 00:23:20,220 is different, it could be dangerous, 381 00:23:20,220 --> 00:23:22,240 especially if you're a preyed upon animal. 382 00:23:26,030 --> 00:23:28,310 Hence, our visual system is highly 383 00:23:28,310 --> 00:23:31,690 attuned to detecting novelty and responding to it. 384 00:23:34,980 --> 00:23:39,910 So next in importance, orienting towards novel objects 385 00:23:39,910 --> 00:23:42,990 to explore them. 386 00:23:42,990 --> 00:23:45,800 So there's a dual role of novelty there. 387 00:23:45,800 --> 00:23:47,920 We have a tendency to explore them. 388 00:23:47,920 --> 00:23:51,386 We have a tendency to be afraid of them. 389 00:23:51,386 --> 00:23:53,680 So it depends on how novel they are, 390 00:23:53,680 --> 00:23:56,252 and the situation, of course. 391 00:23:56,252 --> 00:24:00,710 But obviously we orient in order to find food, 392 00:24:00,710 --> 00:24:03,704 find potential mates or rivals, and so forth. 393 00:24:03,704 --> 00:24:09,600 And finally, identifying animals and objects, 394 00:24:09,600 --> 00:24:12,050 which when we think of vision, that's normally 395 00:24:12,050 --> 00:24:15,023 what we're thinking about, not these other functions. 396 00:24:15,023 --> 00:24:17,430 It doesn't mean humans don't have them. 397 00:24:17,430 --> 00:24:19,650 We do. 398 00:24:19,650 --> 00:24:22,000 All right. 399 00:24:22,000 --> 00:24:25,290 So now I want you to recall the hypothesis, using 400 00:24:25,290 --> 00:24:28,470 Darwinian logic, concerning the evolution of predominantly 401 00:24:28,470 --> 00:24:31,883 crossed representation of visual space. 402 00:24:31,883 --> 00:24:35,960 Can any of you remember that when we talked about it before? 403 00:24:35,960 --> 00:24:37,262 Let's just go over it. 404 00:24:42,360 --> 00:24:45,090 I claim it was an early evolution of connections 405 00:24:45,090 --> 00:24:48,990 that carry information, of things 406 00:24:48,990 --> 00:24:55,020 like a sudden appearance of shadows on one side, 407 00:24:55,020 --> 00:24:56,950 or triggering escape movements. 408 00:25:01,190 --> 00:25:03,250 The most direct, relevant connection 409 00:25:03,250 --> 00:25:09,056 from the eye to the escape mechanism for turning away 410 00:25:09,056 --> 00:25:11,870 was a cross projection. 411 00:25:11,870 --> 00:25:13,390 And this is the way I represent it. 412 00:25:13,390 --> 00:25:16,270 These are the pictures. 413 00:25:16,270 --> 00:25:19,210 Here I put the spinoreticular pathway. 414 00:25:19,210 --> 00:25:22,050 I discovered this morning that I had this reversed, 415 00:25:22,050 --> 00:25:25,400 so I did a mirror image and changed the words. 416 00:25:25,400 --> 00:25:28,639 That's why spinoreticular I think in the book 417 00:25:28,639 --> 00:25:30,530 is on the left. 418 00:25:30,530 --> 00:25:32,900 But anyway, here's the spinoreticular. 419 00:25:32,900 --> 00:25:38,940 It's an ipsilateral pathway, but to a lesser degree, 420 00:25:38,940 --> 00:25:40,345 it's bilateral. 421 00:25:40,345 --> 00:25:44,530 It goes to both sides, but mainly ipsilateral. 422 00:25:44,530 --> 00:25:48,836 Trigeminoreticular is similar-- mostly ipsilateral for input 423 00:25:48,836 --> 00:25:53,310 from the face, ipsilateral but some fibers going 424 00:25:53,310 --> 00:25:55,740 to the other side. 425 00:25:55,740 --> 00:25:57,920 Now, in this picture, on the left, 426 00:25:57,920 --> 00:26:01,875 here I show the primitive retinal projections. 427 00:26:01,875 --> 00:26:04,370 They've just reached the hypothalamus. 428 00:26:04,370 --> 00:26:06,000 They're going to that suprachiasmatic, 429 00:26:06,000 --> 00:26:08,950 and I show them just as they are now. 430 00:26:08,950 --> 00:26:11,420 I don't think there's been any change. 431 00:26:11,420 --> 00:26:15,430 A wide range of animals, they've looked at this kind of pathway. 432 00:26:15,430 --> 00:26:19,630 It's always like this, bilateral. 433 00:26:19,630 --> 00:26:23,750 And I show it the way it is in the rodents and other mammals 434 00:26:23,750 --> 00:26:25,050 they've studied. 435 00:26:25,050 --> 00:26:28,564 Pretty much equally to the two sides. 436 00:26:28,564 --> 00:26:29,980 And here's the trigeminoreticular. 437 00:26:33,930 --> 00:26:45,230 So to escape from something over here, 438 00:26:45,230 --> 00:26:47,975 you want the first movement to be turning away, 439 00:26:47,975 --> 00:26:51,100 and you want, at almost the same time, 440 00:26:51,100 --> 00:26:54,600 you want it to trigger locomotion, 441 00:26:54,600 --> 00:27:00,200 rapid locomtion, this. 442 00:27:00,200 --> 00:27:03,010 Turning away and swimming rapidly. 443 00:27:03,010 --> 00:27:05,920 And that's exactly-- there's been some detailed studies 444 00:27:05,920 --> 00:27:09,560 in the sea lamprey, a very primitive vertebrate, 445 00:27:09,560 --> 00:27:15,312 at Northeastern University and some other places as well. 446 00:27:15,312 --> 00:27:22,030 And if you look at their-- they take these rapid video images, 447 00:27:22,030 --> 00:27:26,950 you'll see this bending of the animal first, 448 00:27:26,950 --> 00:27:34,300 and the tail began to lash to propel the animal forward. 449 00:27:34,300 --> 00:27:37,560 So because it's a cross pathway that 450 00:27:37,560 --> 00:27:42,350 can reach those neurons first, that 451 00:27:42,350 --> 00:27:46,670 gave the evolutionary advantage to the cross projections. 452 00:27:46,670 --> 00:27:50,340 And we know that when they eye got bigger, generally, 453 00:27:50,340 --> 00:27:52,190 the bigger a structure is, the more 454 00:27:52,190 --> 00:27:55,945 connections it forms in development. 455 00:27:55,945 --> 00:27:59,364 So some of the axons extended further. 456 00:27:59,364 --> 00:28:00,780 Some of them reach structures that 457 00:28:00,780 --> 00:28:01,988 can trigger escape movements. 458 00:28:01,988 --> 00:28:04,375 And we'll talk in a minute about what 459 00:28:04,375 --> 00:28:06,740 those neurons were early on. 460 00:28:06,740 --> 00:28:10,670 But the main thing is that it was faster across. 461 00:28:10,670 --> 00:28:12,260 OK. 462 00:28:12,260 --> 00:28:18,680 Now, this is a simple picture on that mammalian brain diagram 463 00:28:18,680 --> 00:28:21,000 I've used before in the class, just 464 00:28:21,000 --> 00:28:27,670 to show you all of the retinal projections in vertebrates. 465 00:28:27,670 --> 00:28:30,920 When I say all, I'm not including these very sparse 466 00:28:30,920 --> 00:28:35,360 ones that we know exist here around the suprachiasmatic 467 00:28:35,360 --> 00:28:39,560 nucleus, and they do exist around other nuclei too. 468 00:28:39,560 --> 00:28:45,080 And there's a few that vary a bit from species to species, 469 00:28:45,080 --> 00:28:48,740 and they vary even among animals within a species. 470 00:28:48,740 --> 00:28:53,160 So I am not talking about those. 471 00:28:53,160 --> 00:28:57,095 These are the ones you keep seeing in animal after animal 472 00:28:57,095 --> 00:29:00,680 after animal-- all the vertebrates. 473 00:29:00,680 --> 00:29:03,430 Here's the one to the hypothalamus. 474 00:29:03,430 --> 00:29:05,740 This is the lateral geniculate body. 475 00:29:05,740 --> 00:29:08,972 And you notice that there's two nuclei there. 476 00:29:08,972 --> 00:29:14,140 The one we always hear about is the dorsal nucleus. 477 00:29:14,140 --> 00:29:16,670 But that's the one that projects it to the visual cortex 478 00:29:16,670 --> 00:29:19,500 up here, and I show that pathway. 479 00:29:19,500 --> 00:29:22,600 Then the axons continue. 480 00:29:22,600 --> 00:29:27,456 They reach the area in front of the superior colliculus, 481 00:29:27,456 --> 00:29:32,210 or optic tectum in most animals. 482 00:29:32,210 --> 00:29:35,020 And then they reach the optic tectum, labeled SC here 483 00:29:35,020 --> 00:29:39,560 for superior colliculus, because this is a mammal. 484 00:29:39,560 --> 00:29:42,980 Pretectal area has a number of different cell groups 485 00:29:42,980 --> 00:29:45,431 that have different functions. 486 00:29:45,431 --> 00:29:47,060 But we can lump them together. 487 00:29:47,060 --> 00:29:49,620 It's part-- at least, in the way I treat it in my book, 488 00:29:49,620 --> 00:29:53,750 it's part of the epithalamus because there's 489 00:29:53,750 --> 00:29:57,820 various structural data that say that both 490 00:29:57,820 --> 00:30:01,970 the nuclei and the pretectal cell groups and the posterior 491 00:30:01,970 --> 00:30:05,810 commissure region are all part of the epithalamus. 492 00:30:05,810 --> 00:30:10,990 But modern molecular studies, they vary a lot. 493 00:30:10,990 --> 00:30:13,980 But these people tend to say epithalamus is just 494 00:30:13,980 --> 00:30:19,330 [INAUDIBLE], and they call the pretectal area something else. 495 00:30:19,330 --> 00:30:23,100 But being an anatomist person first and foremost and not 496 00:30:23,100 --> 00:30:26,100 a molecular person that skips over the first 500 497 00:30:26,100 --> 00:30:30,465 years of neuroscience, I say that no, it's all epithalamus. 498 00:30:30,465 --> 00:30:30,964 Sorry. 499 00:30:33,680 --> 00:30:34,290 OK. 500 00:30:34,290 --> 00:30:36,940 So what is the structure that first 501 00:30:36,940 --> 00:30:38,680 controlled escape reactions? 502 00:30:38,680 --> 00:30:42,330 Well, here the shortest axons are 503 00:30:42,330 --> 00:30:45,050 reaching the suprachiasmatic nucleus. 504 00:30:45,050 --> 00:30:48,439 And we've talked about tectum being important for escape 505 00:30:48,439 --> 00:30:50,480 movements, but look at all these other structures 506 00:30:50,480 --> 00:30:52,400 they go through first. 507 00:30:52,400 --> 00:30:55,430 So was the tectum really the first? 508 00:30:55,430 --> 00:31:01,410 So I began to look at this nucleus, the first one 509 00:31:01,410 --> 00:31:04,690 beyond the suprachiasmatic nucleus 510 00:31:04,690 --> 00:31:06,780 if I don't include this little offshoot here. 511 00:31:06,780 --> 00:31:09,390 We know quite a bit about the functions of that. 512 00:31:09,390 --> 00:31:12,750 It's the accessory optic tract, and we'll 513 00:31:12,750 --> 00:31:15,350 hear more about that next time. 514 00:31:15,350 --> 00:31:17,570 Those are axons that leave the main optic tract, 515 00:31:17,570 --> 00:31:20,212 so let's just stick with the main optic tract 516 00:31:20,212 --> 00:31:23,340 and look at that. 517 00:31:23,340 --> 00:31:26,153 What structure first controlled escape reactions? 518 00:31:26,153 --> 00:31:30,250 So we know the midbrain tectum with the superior colliculus, 519 00:31:30,250 --> 00:31:33,110 is the dominant structure now. 520 00:31:36,310 --> 00:31:38,230 I believe that's true even in humans. 521 00:31:38,230 --> 00:31:42,015 If you have the instinctive escape reaction to a novel 522 00:31:42,015 --> 00:31:44,210 object. 523 00:31:44,210 --> 00:31:49,960 Most of us don't have any memory of experiencing that, 524 00:31:49,960 --> 00:31:52,130 but I was a pretty observant little kid, 525 00:31:52,130 --> 00:31:59,060 and I remember suddenly-- I used to also think a lot. 526 00:31:59,060 --> 00:32:02,000 I thought too much, so sometimes I wasn't paying attention. 527 00:32:02,000 --> 00:32:04,120 And I got right in front of a car once, 528 00:32:04,120 --> 00:32:07,150 and he was coming pretty fast right at me. 529 00:32:07,150 --> 00:32:11,510 I had a sudden, instinctive reaction. 530 00:32:11,510 --> 00:32:16,230 I froze, and I could not move the handlebars at all, 531 00:32:16,230 --> 00:32:17,660 even though I wanted to. 532 00:32:17,660 --> 00:32:21,650 My cognitive system said turn away, get out in front of this. 533 00:32:21,650 --> 00:32:24,240 But I was frozen. 534 00:32:24,240 --> 00:32:29,170 Freezing is a typical anti-predator response 535 00:32:29,170 --> 00:32:33,280 of young animals, even big ones, like us. 536 00:32:33,280 --> 00:32:34,440 I was pretty young. 537 00:32:34,440 --> 00:32:35,835 I froze. 538 00:32:35,835 --> 00:32:37,010 I could not move. 539 00:32:37,010 --> 00:32:40,550 Thank God the guy at the wheel didn't just freeze. 540 00:32:40,550 --> 00:32:42,265 He put his brakes on and he stopped. 541 00:32:42,265 --> 00:32:44,181 And he didn't hit me. 542 00:32:44,181 --> 00:32:44,680 All right. 543 00:32:44,680 --> 00:32:48,190 So that's a tectal response, and that's what animals do. 544 00:32:48,190 --> 00:32:50,470 I've studied it in animals. 545 00:32:50,470 --> 00:32:52,510 But then they reach the LGV here, 546 00:32:52,510 --> 00:32:56,250 the ventral nucleus of the lateral geniculate. 547 00:32:56,250 --> 00:33:01,350 And I discovered that it's part of the subthalamus-- 548 00:33:01,350 --> 00:33:03,760 well, the more medial part of the subthalamus. 549 00:33:03,760 --> 00:33:08,130 And there are connections there, from the visual part, 550 00:33:08,130 --> 00:33:12,675 that if you stimulate, you can get very rapid running 551 00:33:12,675 --> 00:33:13,770 movements. 552 00:33:13,770 --> 00:33:15,440 Everybody's ignored it. 553 00:33:15,440 --> 00:33:19,476 Visual people just focus on the popular things-- 554 00:33:19,476 --> 00:33:24,820 superior colliculus, lateral geniculate body, visual cortex. 555 00:33:24,820 --> 00:33:29,490 But I love these things that people ignore. 556 00:33:29,490 --> 00:33:31,620 In evolution, these things are very important. 557 00:33:31,620 --> 00:33:34,990 It turns out, that area of the subthalamus 558 00:33:34,990 --> 00:33:38,130 has direct projections to the midbrain locomotor area. 559 00:33:40,900 --> 00:33:46,435 That's how the locomotion, the very short latency pathway, 560 00:33:46,435 --> 00:33:49,690 is produced-- from this area. 561 00:33:49,690 --> 00:33:53,810 But now we know that it's the pathways from the tectum that 562 00:33:53,810 --> 00:33:57,570 also have a rapidly conducting ipsilateral pathway 563 00:33:57,570 --> 00:34:00,840 to the midbrain locomotor area that 564 00:34:00,840 --> 00:34:06,300 has become dominant, because the tectum is so much bigger. 565 00:34:06,300 --> 00:34:09,909 So often something becomes dominant because of its size. 566 00:34:09,909 --> 00:34:13,206 It doesn't mean that the ventral lateral geniculate 567 00:34:13,206 --> 00:34:15,750 body is important, but it's become 568 00:34:15,750 --> 00:34:17,929 overshadowed by the larger structure. 569 00:34:17,929 --> 00:34:21,400 They both have connections to that area. 570 00:34:21,400 --> 00:34:25,190 So next, orienting towards novel objects, for exploring, 571 00:34:25,190 --> 00:34:27,650 for finding food, for finding a mate, 572 00:34:27,650 --> 00:34:33,414 finding a rival, for finding the doorknob 573 00:34:33,414 --> 00:34:36,480 so you can get out the door. 574 00:34:36,480 --> 00:34:37,140 All right. 575 00:34:41,530 --> 00:34:44,010 This is the question I wrote-- contrast 576 00:34:44,010 --> 00:34:46,560 the type of visual orienting for which the midbrain 577 00:34:46,560 --> 00:34:51,199 tectum or colliculus has become dominant in most species 578 00:34:51,199 --> 00:34:55,009 and the visual orienting for which the pretectal area is 579 00:34:55,009 --> 00:34:56,622 important. 580 00:34:56,622 --> 00:34:59,560 Now, the problem here is that it's only 581 00:34:59,560 --> 00:35:03,150 been discovered in a few species-- mainly two. 582 00:35:03,150 --> 00:35:08,000 Discovered first in frogs, verified for a mammal. 583 00:35:08,000 --> 00:35:11,940 But let's go through these. 584 00:35:11,940 --> 00:35:14,910 First, the main type of orienting. 585 00:35:14,910 --> 00:35:18,265 You see something here, you turn towards it. 586 00:35:18,265 --> 00:35:19,390 You do that with a hamster. 587 00:35:19,390 --> 00:35:23,010 Remember, this is, I think, chapter 13, I 588 00:35:23,010 --> 00:35:25,530 talked about the regeneration of the optic tract, 589 00:35:25,530 --> 00:35:28,630 and I showed you these videos of hamsters turning. 590 00:35:28,630 --> 00:35:31,135 All those turning movements are controlled by the tectum. 591 00:35:31,135 --> 00:35:35,535 The hamster can't turn at all without the projection 592 00:35:35,535 --> 00:35:37,680 from retina to tectum. 593 00:35:37,680 --> 00:35:39,735 There is input coming from visual cortex, 594 00:35:39,735 --> 00:35:43,920 but it comes in through this same route, 595 00:35:43,920 --> 00:35:48,230 from the front of the tectum into those superficial layers. 596 00:35:48,230 --> 00:35:53,790 So the left eye we want to control something's out here, 597 00:35:53,790 --> 00:35:57,710 say a sunflower seed. 598 00:35:57,710 --> 00:36:02,075 It's mainly a crossed pathway because of that evolution 599 00:36:02,075 --> 00:36:03,820 we talked about earlier. 600 00:36:03,820 --> 00:36:06,880 So it's going to the right superior colliculus. 601 00:36:06,880 --> 00:36:09,125 So to control, turning to the left, 602 00:36:09,125 --> 00:36:14,395 he has to contract the muscles, activate motor 603 00:36:14,395 --> 00:36:16,475 neurons on the left side of the spinal cord. 604 00:36:16,475 --> 00:36:20,445 He does that by the crossed pathway, tectospinal pathway. 605 00:36:20,445 --> 00:36:25,299 So to turn left, it crosses once here, crosses again here. 606 00:36:28,610 --> 00:36:35,610 And was the tectum always dominant? 607 00:36:35,610 --> 00:36:38,890 You can ask that same question we asked before. 608 00:36:38,890 --> 00:36:43,970 I think the LGV was probably important early on, 609 00:36:43,970 --> 00:36:49,856 but it clearly is not so dominant now. 610 00:36:49,856 --> 00:36:55,790 So it's this tectum that's the major structure for that. 611 00:36:55,790 --> 00:36:58,630 Now, whatever it was in very early evolution. 612 00:37:03,430 --> 00:37:06,190 It reaches subthalamus first. 613 00:37:06,190 --> 00:37:07,790 Then it goes through the thalamus. 614 00:37:07,790 --> 00:37:13,130 But that, the dorsal thalamus, the lateral geniculate body, 615 00:37:13,130 --> 00:37:15,035 doesn't have these same projections. 616 00:37:15,035 --> 00:37:20,100 It only projects to the endbrain, 617 00:37:20,100 --> 00:37:22,000 mainly to the visual cortex. 618 00:37:25,330 --> 00:37:30,000 So let's talk about the pretectal area. 619 00:37:30,000 --> 00:37:32,700 And this is an interesting structure, because remember, 620 00:37:32,700 --> 00:37:34,500 I said it had multiple cell groups. 621 00:37:34,500 --> 00:37:36,730 And they had different functions. 622 00:37:36,730 --> 00:37:39,060 We know, for example, tat there's 623 00:37:39,060 --> 00:37:44,750 a superficial part of it that projects 624 00:37:44,750 --> 00:37:49,490 into the nucleus of the parasympathetic system that 625 00:37:49,490 --> 00:37:57,880 then projects to the ciliary ganglion behind the eye, 626 00:37:57,880 --> 00:38:03,060 that when that's activated it causes pupillary constriction. 627 00:38:03,060 --> 00:38:05,500 That's the pupillary light reflex. 628 00:38:05,500 --> 00:38:08,050 You shine a light in the eye, the pupil constricts. 629 00:38:11,040 --> 00:38:16,650 You're in the dark, that is not active, the pupils expand. 630 00:38:16,650 --> 00:38:19,920 Or if you get angry, the pupils expand. 631 00:38:19,920 --> 00:38:24,370 You bring in more light at the expense of acuity. 632 00:38:24,370 --> 00:38:26,540 It's important to get the maximum light. 633 00:38:32,860 --> 00:38:37,350 And if you're talking to a girl or you're talking to a man, 634 00:38:37,350 --> 00:38:40,530 you want to know how interested they are in you, 635 00:38:40,530 --> 00:38:42,870 watch their pupils. 636 00:38:42,870 --> 00:38:45,670 The pupils will get larger if the sympathetic nervous 637 00:38:45,670 --> 00:38:47,560 system-- if they really start to get excited, 638 00:38:47,560 --> 00:38:51,590 the pupils will expand. 639 00:38:51,590 --> 00:38:55,570 If you're a salesperson, there are salespeople 640 00:38:55,570 --> 00:38:57,460 that become sensitive to that, and they 641 00:38:57,460 --> 00:39:01,544 can tell how interested someone is. 642 00:39:01,544 --> 00:39:03,710 And that's important, because they can make a better 643 00:39:03,710 --> 00:39:06,240 deal if they can detect pupils. 644 00:39:09,400 --> 00:39:13,250 But anyway, another function discovered here 645 00:39:13,250 --> 00:39:15,990 in frog and treeshrew-- very interesting, 646 00:39:15,990 --> 00:39:18,020 because it's also a kind of orienting. 647 00:39:18,020 --> 00:39:22,545 If these animals are running along, and there are barriers, 648 00:39:22,545 --> 00:39:26,150 there are poles or sticks or trees in front of them, 649 00:39:26,150 --> 00:39:29,550 they sidestep them. 650 00:39:29,550 --> 00:39:32,680 That's a kind of orienting. 651 00:39:32,680 --> 00:39:34,300 They're sidestepping the barrier. 652 00:39:34,300 --> 00:39:37,400 They're running this way, they go around. 653 00:39:37,400 --> 00:39:40,180 That's not controlled by the tectum. 654 00:39:40,180 --> 00:39:42,150 It's controlled by the pretectal area, 655 00:39:42,150 --> 00:39:44,295 according to some pretty good studies 656 00:39:44,295 --> 00:39:47,720 of the frog and the treeshrew. 657 00:39:47,720 --> 00:39:49,650 So similarly, when the animal has 658 00:39:49,650 --> 00:39:53,360 to run rapidly into an opening, he 659 00:39:53,360 --> 00:39:57,430 uses that system to control his limbs 660 00:39:57,430 --> 00:40:02,470 to get his body aligned during locomotion. 661 00:40:02,470 --> 00:40:04,300 It's not been studied very much. 662 00:40:04,300 --> 00:40:07,370 Certainly deserving a lot more study. 663 00:40:07,370 --> 00:40:12,570 And then the one other function that we know about 664 00:40:12,570 --> 00:40:17,310 is a vestibular light function that when you start to fall 665 00:40:17,310 --> 00:40:22,130 or when you're locomoting and moving your head, 666 00:40:22,130 --> 00:40:24,550 there's stimulation of the entire retina 667 00:40:24,550 --> 00:40:29,310 by the flow of visual images over the retina. 668 00:40:29,310 --> 00:40:34,570 That flow, things that affect the whole retina, 669 00:40:34,570 --> 00:40:37,740 are detected by cells in the accessory optic system 670 00:40:37,740 --> 00:40:41,470 and in a nucleus of pretectal area, 671 00:40:41,470 --> 00:40:43,650 the nucleus of the optic tract. 672 00:40:43,650 --> 00:40:45,480 And that has an important function 673 00:40:45,480 --> 00:40:48,670 that we'll be talking about after we finish audition. 674 00:40:54,340 --> 00:40:57,400 So I say here, distinguish between two very different 675 00:40:57,400 --> 00:40:58,880 functions in the midbrain tectum, 676 00:40:58,880 --> 00:41:01,305 each involving a different output pathway. 677 00:41:01,305 --> 00:41:04,701 But which of these functions is precise acuity more important? 678 00:41:04,701 --> 00:41:06,075 Well, what are the two functions? 679 00:41:06,075 --> 00:41:07,845 We've been talking about them. 680 00:41:14,640 --> 00:41:18,986 Orienting towards something and escaping from something. 681 00:41:18,986 --> 00:41:20,780 Those are the two functions. 682 00:41:20,780 --> 00:41:23,440 We know they have different pathways. 683 00:41:23,440 --> 00:41:27,040 The outputs-- and I talk here about the nature 684 00:41:27,040 --> 00:41:29,230 of the pathways. 685 00:41:29,230 --> 00:41:33,130 Escape from predators involves an ipsilateral pathway 686 00:41:33,130 --> 00:41:34,661 from that tectum. 687 00:41:34,661 --> 00:41:36,410 Remember, the fibers have already crossed. 688 00:41:36,410 --> 00:41:39,290 The retinal fibers have crossed to get to the tectum. 689 00:41:39,290 --> 00:41:41,460 But then there's a short ipsilateral pathway 690 00:41:41,460 --> 00:41:46,430 to the local motor regions that control the escape reaction. 691 00:41:46,430 --> 00:41:49,150 It's that cross pathway that I showed 692 00:41:49,150 --> 00:41:52,040 in this diagram, this one. 693 00:41:52,040 --> 00:41:54,810 This controls turning towards things. 694 00:41:59,380 --> 00:42:00,860 So those are the two functions. 695 00:42:03,460 --> 00:42:08,550 Now, I ask which of those things requires more acuity? 696 00:42:08,550 --> 00:42:15,900 And here, I mean the precision of location, how precisely 697 00:42:15,900 --> 00:42:20,140 does the animal know in the sense that his brain is 698 00:42:20,140 --> 00:42:23,180 detecting the difference, between a thing 699 00:42:23,180 --> 00:42:26,305 in the temporal retina here in front of him, 700 00:42:26,305 --> 00:42:29,740 or in the temporal field or nasal retina 701 00:42:29,740 --> 00:42:32,850 here or two regions close to each other here? 702 00:42:32,850 --> 00:42:37,080 Well, it depends on how precise that topography is, right? 703 00:42:41,390 --> 00:42:45,800 We talk about acuity in the visual cortex likewise. 704 00:42:45,800 --> 00:42:49,130 And it's basically visual acuity. 705 00:42:49,130 --> 00:42:51,950 How fine a difference you can detect 706 00:42:51,950 --> 00:42:56,297 in details of the visual field depends on how much brain there 707 00:42:56,297 --> 00:42:58,900 is representing that part of the visual field. 708 00:42:58,900 --> 00:43:01,950 So we have a lot more brain representing a lot more area 709 00:43:01,950 --> 00:43:05,910 in the cortex devoted to the phobia than areas 710 00:43:05,910 --> 00:43:07,480 off the phobia. 711 00:43:07,480 --> 00:43:10,455 Periphery gets much smaller representation. 712 00:43:10,455 --> 00:43:13,720 But the same thing is true here for the orienting movements, 713 00:43:13,720 --> 00:43:15,240 even though the functions are quite 714 00:43:15,240 --> 00:43:17,590 different in the midbrain. 715 00:43:17,590 --> 00:43:20,955 You still have a kind of acuity. 716 00:43:20,955 --> 00:43:24,405 And here I'm asking, what are the two main methods that 717 00:43:24,405 --> 00:43:28,490 have been used by neuroscientists to map 718 00:43:28,490 --> 00:43:30,480 the topography of the representations 719 00:43:30,480 --> 00:43:35,030 of the visual field and retina in the superior colliculus? 720 00:43:35,030 --> 00:43:36,720 How did I get that map? 721 00:43:36,720 --> 00:43:39,070 This comes from my work. 722 00:43:39,070 --> 00:43:44,800 And this is actually a summary of a lot of work, 723 00:43:44,800 --> 00:43:47,550 with two very different methods. 724 00:43:47,550 --> 00:43:48,570 What are they? 725 00:43:48,570 --> 00:43:53,210 One's anatomical, the other uses electrophysiology. 726 00:43:53,210 --> 00:43:58,195 The most common method is to use electrophysiology, 727 00:43:58,195 --> 00:44:01,610 to put the electrode in, record from the neuron 728 00:44:01,610 --> 00:44:05,700 there in the superficial tectum, and find out 729 00:44:05,700 --> 00:44:08,950 where in the visual field the stimulus has 730 00:44:08,950 --> 00:44:11,470 to be in order to activate those cells. 731 00:44:11,470 --> 00:44:16,050 That's mapping the receptive field of the cells. 732 00:44:16,050 --> 00:44:18,910 And if we're interested in just location, 733 00:44:18,910 --> 00:44:21,410 we don't need to worry about the properties of the stimulus. 734 00:44:21,410 --> 00:44:24,115 We just have to find usually a little dark spot 735 00:44:24,115 --> 00:44:25,700 on the light background. 736 00:44:25,700 --> 00:44:28,660 Or it can be a bright spot on the dark background. 737 00:44:28,660 --> 00:44:32,240 The dark spots tend to work the best. 738 00:44:32,240 --> 00:44:35,090 You can easily map the visual field. 739 00:44:35,090 --> 00:44:37,930 But you can also make-- if you want 740 00:44:37,930 --> 00:44:45,040 to see at once the projection throughout the entire optic 741 00:44:45,040 --> 00:44:48,890 tract, you can make a lesion in the eye 742 00:44:48,890 --> 00:44:51,070 or an injection of a tracer. 743 00:44:51,070 --> 00:44:55,140 You've got to label axons from one part of the retina. 744 00:44:55,140 --> 00:44:59,140 So here's the retina, here's the optic disc. 745 00:44:59,140 --> 00:45:03,962 Let's say you make a lesion here in the retina. 746 00:45:03,962 --> 00:45:10,610 The fibers from out here, though, are all damaged too. 747 00:45:10,610 --> 00:45:13,315 So the effective lesion is like that 748 00:45:13,315 --> 00:45:17,470 when you make a hole in the retina like that. 749 00:45:17,470 --> 00:45:22,880 You can then trace the axons from the retina 750 00:45:22,880 --> 00:45:26,380 to a corresponding area. 751 00:45:26,380 --> 00:45:30,510 You'll find the axons in the superior colliculus 752 00:45:30,510 --> 00:45:33,660 to be in an area like that. 753 00:45:33,660 --> 00:45:36,910 So it's only by putting together a number of different cases 754 00:45:36,910 --> 00:45:39,590 like that you can come up with the same map. 755 00:45:39,590 --> 00:45:42,982 But you will then come up with the map simultaneously 756 00:45:42,982 --> 00:45:46,110 for the geniculate body, for the tectum, 757 00:45:46,110 --> 00:45:49,950 for all the structures of the optic tract. 758 00:45:49,950 --> 00:45:52,305 That's the advantage of the anatomical method. 759 00:46:09,740 --> 00:46:12,180 So finally the function of identifying 760 00:46:12,180 --> 00:46:14,384 animals and objects. 761 00:46:14,384 --> 00:46:16,050 And I point out here that the colliculus 762 00:46:16,050 --> 00:46:19,600 of the midbrain and the visual cortex areas 763 00:46:19,600 --> 00:46:21,496 are each important for identification 764 00:46:21,496 --> 00:46:23,490 of the [? stimulus ?]. 765 00:46:23,490 --> 00:46:26,340 I know we say it's always cortex, 766 00:46:26,340 --> 00:46:29,220 and I want to explain why that is. 767 00:46:29,220 --> 00:46:32,820 Because identification in the tectum and the pretectum 768 00:46:32,820 --> 00:46:37,240 too involves what we call innate releasing [INAUDIBLE]. 769 00:46:37,240 --> 00:46:42,590 It's innate behavior, instinctive identification. 770 00:46:42,590 --> 00:46:47,566 For example, the best example is the bug detectors in the frog. 771 00:46:47,566 --> 00:46:51,925 A small little area in the visual field 772 00:46:51,925 --> 00:46:55,390 that's dark and moving around. 773 00:46:55,390 --> 00:46:57,950 There are neurons in the frog tectum that respond. 774 00:46:57,950 --> 00:47:01,970 And the frog sits there still and [INAUDIBLE], 775 00:47:01,970 --> 00:47:06,160 because his neurons are responding to that fly. 776 00:47:06,160 --> 00:47:11,930 But he won't snap with his tongue until it stops. 777 00:47:11,930 --> 00:47:16,090 The neurons keep firing for a little while. 778 00:47:16,090 --> 00:47:24,890 Then his mouth opens, and the tongue zaps the fly. 779 00:47:24,890 --> 00:47:28,050 It's an innate mechanism. 780 00:47:28,050 --> 00:47:35,140 Whereas learned identification abilities with greater acuity 781 00:47:35,140 --> 00:47:38,200 follow the invasion of the endbrain 782 00:47:38,200 --> 00:47:41,180 by the visual pathways to the striatum and the cortex, 783 00:47:41,180 --> 00:47:42,470 especially the cortex. 784 00:47:42,470 --> 00:47:44,345 And these are just examples. 785 00:47:44,345 --> 00:47:47,590 The hamster learns to use visual landmarks 786 00:47:47,590 --> 00:47:52,200 to locomote towards its home or to find food and water. 787 00:47:52,200 --> 00:47:54,160 He can't just inherit all that. 788 00:47:54,160 --> 00:47:56,100 He might have innate preferences. 789 00:47:56,100 --> 00:48:00,035 He has innate preferences to go out at a certain time of day 790 00:48:00,035 --> 00:48:03,110 and maybe to go to certain places. 791 00:48:03,110 --> 00:48:07,110 But he also has to learn about where the dangerous places are, 792 00:48:07,110 --> 00:48:09,850 where the safe places are, where's the water, 793 00:48:09,850 --> 00:48:13,490 or where are the fruits that he can get liquid from, 794 00:48:13,490 --> 00:48:15,340 and things like that. 795 00:48:15,340 --> 00:48:17,070 Where are the grains? 796 00:48:17,070 --> 00:48:19,365 Where's the farmer's grain storage 797 00:48:19,365 --> 00:48:24,220 that he can go rob and fill his cheek pouches. 798 00:48:24,220 --> 00:48:26,062 And we know that some animals learn 799 00:48:26,062 --> 00:48:29,140 to recognize members of their own species 800 00:48:29,140 --> 00:48:31,630 as individuals, just by visual differences. 801 00:48:36,860 --> 00:48:38,820 So I'm asking here, why? 802 00:48:38,820 --> 00:48:41,340 Relatively recently in evolutionary time 803 00:48:41,340 --> 00:48:46,340 have these visual identification abilities evolved so much. 804 00:48:46,340 --> 00:48:50,820 And I point out that with these larger topographic maps, when 805 00:48:50,820 --> 00:48:53,680 you have precise topography, you then 806 00:48:53,680 --> 00:48:55,700 in the projections from that structure, 807 00:48:55,700 --> 00:49:00,070 you just have to combine inputs in specific ways 808 00:49:00,070 --> 00:49:03,260 to get some kind of shape and pattern recognition. 809 00:49:03,260 --> 00:49:06,655 And that has been studied most extensively for visual cortex 810 00:49:06,655 --> 00:49:10,610 in work-- initially it was done in the frog by Jerry Lettvin 811 00:49:10,610 --> 00:49:13,590 here at MIT, and then it was done at Harvard 812 00:49:13,590 --> 00:49:17,470 in the visual cortex of cats and later in monkeys 813 00:49:17,470 --> 00:49:19,430 by [INAUDIBLE]. 814 00:49:19,430 --> 00:49:21,380 And in your vision classes, you always 815 00:49:21,380 --> 00:49:22,463 learn about those studies. 816 00:49:25,680 --> 00:49:26,180 OK. 817 00:49:33,300 --> 00:49:36,970 Visual pathways to the endbrain follow multiple roots. 818 00:49:36,970 --> 00:49:39,720 I want you to be able to describe more than just 819 00:49:39,720 --> 00:49:43,610 the two traditional roots, because everybody 820 00:49:43,610 --> 00:49:45,470 knows about two of them. 821 00:49:45,470 --> 00:49:49,240 There's actually, like, six, and I describe them 822 00:49:49,240 --> 00:49:50,070 all in the book. 823 00:49:52,910 --> 00:49:56,430 And I just summarize them here. 824 00:49:56,430 --> 00:49:57,980 Tectum and pretectum each project 825 00:49:57,980 --> 00:50:00,550 to the older parts of the thalamus, which 826 00:50:00,550 --> 00:50:04,510 project to both cortex and striatum. 827 00:50:04,510 --> 00:50:06,435 And they also project to the newer parts 828 00:50:06,435 --> 00:50:12,140 of the thalamus of mammals. 829 00:50:12,140 --> 00:50:16,300 And then the retina projects directly to the thalamus also, 830 00:50:16,300 --> 00:50:20,010 mainly geniculate body. 831 00:50:20,010 --> 00:50:28,690 So that gives multiple projections for visual stimuli 832 00:50:28,690 --> 00:50:30,880 to get to the endbrain. 833 00:50:34,640 --> 00:50:36,990 So that's just summarized here. 834 00:50:36,990 --> 00:50:39,910 And this just shows a picture of the projection 835 00:50:39,910 --> 00:50:42,510 from a cell in one of those intralaminar nuclei. 836 00:50:42,510 --> 00:50:45,570 And I picked this one because it gets input from the colliculus 837 00:50:45,570 --> 00:50:48,450 that I've seen in my studies of hamsters. 838 00:50:48,450 --> 00:50:52,240 And here it shows the axon going to corpus striatum 839 00:50:52,240 --> 00:50:55,360 and to the neocortex. 840 00:50:55,360 --> 00:50:57,340 Most of them don't go to both places. 841 00:50:57,340 --> 00:50:59,300 They go to one of those two. 842 00:50:59,300 --> 00:51:03,090 But some of them actually go to both. 843 00:51:03,090 --> 00:51:05,620 And then I just go through the adaptive advantages 844 00:51:05,620 --> 00:51:09,126 of this for reaching the striatum, 845 00:51:09,126 --> 00:51:12,865 reaching the neocortex, and the cognitive functions 846 00:51:12,865 --> 00:51:14,700 in the projections of those areas. 847 00:51:17,395 --> 00:51:19,340 And then [INAUDIBLE] to your vision also, 848 00:51:19,340 --> 00:51:20,750 which developed cortical projections better 849 00:51:20,750 --> 00:51:21,375 than any place. 850 00:51:24,490 --> 00:51:26,120 So you can read the rest of this. 851 00:51:26,120 --> 00:51:28,760 I think it's very clear in the book. 852 00:51:28,760 --> 00:51:30,620 And we'll do the retinal projections. 853 00:51:30,620 --> 00:51:34,858 We'll look at pictures other than this next time 854 00:51:34,858 --> 00:51:36,762 to go through that. 855 00:51:36,762 --> 00:51:38,550 I'll post all these slides. 856 00:51:38,550 --> 00:51:41,090 I've already posted them. 857 00:51:41,090 --> 00:51:44,320 I may add a few notes to them after the class. 858 00:51:44,320 --> 00:51:49,016 So now for next time, read that next chapter. 859 00:51:49,016 --> 00:51:55,080 You were supposed to read chapter 20, was it, for today? 860 00:51:55,080 --> 00:51:56,845 The first vision chapter. 861 00:51:59,490 --> 00:52:05,340 And then, yeah, 19 was the olfactory chapter. 862 00:52:05,340 --> 00:52:09,110 So read chapter 21 also for next time. 863 00:52:09,110 --> 00:52:10,997 And I'll come up with some homework. 864 00:52:13,977 --> 00:52:14,893 AUDIENCE: [INAUDIBLE]. 865 00:52:32,294 --> 00:52:36,610 PROFESSOR: No, I don't plan on giving a quiz, 866 00:52:36,610 --> 00:52:38,530 but I plan on giving you some homework. 867 00:52:41,799 --> 00:52:42,340 I don't know. 868 00:52:42,340 --> 00:52:45,530 My impression is that you're happy with the homework 869 00:52:45,530 --> 00:52:47,990 and you probably learn more. 870 00:52:47,990 --> 00:52:51,520 I can give you an assortment of things.