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 --> 00:00:17,230 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:17,230 --> 00:00:17,855 at ocw.mit.edu. 8 00:00:23,090 --> 00:00:25,640 PROFESSOR: This is class four. 9 00:00:25,640 --> 00:00:30,780 I want to start with that simple neural tube we saw already 10 00:00:30,780 --> 00:00:35,010 in this little creature, amphioxis. 11 00:00:35,010 --> 00:00:38,842 The lancelets is another common name 12 00:00:38,842 --> 00:00:42,500 you can call that group of animals. 13 00:00:42,500 --> 00:00:49,775 And ask this question-- we don't have fossils of the brains. 14 00:00:52,310 --> 00:00:54,556 Brain is soft tissue, doesn't leave fossils. 15 00:00:59,580 --> 00:01:03,775 So when most of our ancestors are extinct, 16 00:01:03,775 --> 00:01:07,650 how do we know anything about brain evolution? 17 00:01:10,460 --> 00:01:11,910 Somebody want to tell me? 18 00:01:21,930 --> 00:01:25,312 How much can we tell about the brain from the skull? 19 00:01:25,312 --> 00:01:26,228 AUDIENCE: [INAUDIBLE]. 20 00:01:32,870 --> 00:01:33,870 PROFESSOR: That's right. 21 00:01:33,870 --> 00:01:35,340 Exactly. 22 00:01:35,340 --> 00:01:36,115 Another comment? 23 00:01:48,120 --> 00:01:50,385 OK, I can hardly hear you because of the background 24 00:01:50,385 --> 00:01:52,399 noise. 25 00:01:52,399 --> 00:01:53,315 AUDIENCE: [INAUDIBLE]. 26 00:02:07,790 --> 00:02:09,620 PROFESSOR: And you can see evidence 27 00:02:09,620 --> 00:02:11,722 of that in skulls, that's right. 28 00:02:11,722 --> 00:02:14,450 So we know. 29 00:02:14,450 --> 00:02:18,260 But there's another factor that nobody's mentioned. 30 00:02:18,260 --> 00:02:19,226 Yes? 31 00:02:19,226 --> 00:02:20,142 AUDIENCE: [INAUDIBLE]. 32 00:02:33,220 --> 00:02:36,330 PROFESSOR: Let's talk about development next time. 33 00:02:36,330 --> 00:02:38,750 We might get to it at the end of this class, 34 00:02:38,750 --> 00:02:40,070 but that's important. 35 00:02:40,070 --> 00:02:42,764 It's very important, and we will talk more about it. 36 00:02:42,764 --> 00:02:43,930 Did you have something else? 37 00:02:48,120 --> 00:02:50,982 No, you go ahead, since she's already-- 38 00:02:50,982 --> 00:02:51,898 AUDIENCE: [INAUDIBLE]. 39 00:03:01,649 --> 00:03:02,440 PROFESSOR: Exactly. 40 00:03:02,440 --> 00:03:07,230 And do you know how we judge how primitive they are? 41 00:03:07,230 --> 00:03:10,540 You can do a lot from skulls if you have the skulls, 42 00:03:10,540 --> 00:03:15,630 because they look the same as skulls. 43 00:03:15,630 --> 00:03:17,620 We can pretty much identify the species 44 00:03:17,620 --> 00:03:21,140 by skull details and skeletal details. 45 00:03:21,140 --> 00:03:25,140 And if they're relatively unchanged over millions 46 00:03:25,140 --> 00:03:29,460 of years, we can get an idea of how ancient they are. 47 00:03:29,460 --> 00:03:32,540 And then, if we can get any DNA, we 48 00:03:32,540 --> 00:03:35,425 can actually just-- this is, of course, fairly recent. 49 00:03:35,425 --> 00:03:42,730 You can learn a lot about their age 50 00:03:42,730 --> 00:03:48,870 because the rate of mutations is fairly steady. 51 00:03:48,870 --> 00:03:51,780 And if we can get an idea of what their proteins were 52 00:03:51,780 --> 00:03:54,710 like from the DNA, we can learn a lot 53 00:03:54,710 --> 00:03:57,370 about evolution [INAUDIBLE]. 54 00:03:57,370 --> 00:04:02,510 But anyway, I have another question here. 55 00:04:02,510 --> 00:04:05,830 In the early evolution of the chordate neural tube, 56 00:04:05,830 --> 00:04:09,230 what was it that led to the changes at the rostral end? 57 00:04:09,230 --> 00:04:13,940 We saw amphioxis, there's no real enlargement here. 58 00:04:13,940 --> 00:04:16,420 Turns out there are genetic differences, 59 00:04:16,420 --> 00:04:19,469 there are differences in details of neural structure. 60 00:04:22,170 --> 00:04:27,711 But what was it that led to a real brain? 61 00:04:27,711 --> 00:04:34,151 What was the basic thing about these bilaterally symmetric 62 00:04:34,151 --> 00:04:34,650 animals? 63 00:04:37,874 --> 00:04:38,790 AUDIENCE: [INAUDIBLE]. 64 00:04:42,999 --> 00:04:43,790 PROFESSOR: Exactly. 65 00:04:43,790 --> 00:04:47,795 So yes, and that led to the evolution 66 00:04:47,795 --> 00:04:52,370 of specialized receptor systems, which then records 67 00:04:52,370 --> 00:04:57,150 special motor control at the rostral end. 68 00:04:57,150 --> 00:04:59,295 So both the sensory analyzing mechanisms, 69 00:04:59,295 --> 00:05:03,302 the inputs came in through cranial nerves now, 70 00:05:03,302 --> 00:05:05,250 which turned out to be a little different 71 00:05:05,250 --> 00:05:06,430 from the spinal nerves. 72 00:05:06,430 --> 00:05:08,040 We'll be talking about both kinds 73 00:05:08,040 --> 00:05:11,180 of nerves quite a bit in the class. 74 00:05:11,180 --> 00:05:13,790 And then, of course, the motor apparatus they needed. 75 00:05:13,790 --> 00:05:16,900 But also, of course, they needed to maintain 76 00:05:16,900 --> 00:05:18,980 the stability of the internal [INAUDIBLE]. 77 00:05:18,980 --> 00:05:26,046 And that also got very evolved, even starting with amphioxis. 78 00:05:26,046 --> 00:05:29,440 There were secretory systems in that rostral end 79 00:05:29,440 --> 00:05:34,380 of the tube-- the predecessor to the pituitary and hypothalamus. 80 00:05:38,460 --> 00:05:41,250 And the sensory inputs, the ones we think of the most, 81 00:05:41,250 --> 00:05:43,794 are the ones that come in directly 82 00:05:43,794 --> 00:05:49,555 to the forebrain, the olfactory and visual inputs. 83 00:05:53,224 --> 00:05:55,390 And then I've already mentioned the visceral control 84 00:05:55,390 --> 00:05:58,410 that also involved that area. 85 00:05:58,410 --> 00:06:00,110 So here's my little sketch. 86 00:06:03,110 --> 00:06:05,320 It's a very simple neural tube. 87 00:06:05,320 --> 00:06:08,103 And then expansions at the rostral end. 88 00:06:08,103 --> 00:06:10,800 I just sketched here olfactory and visual inputs. 89 00:06:10,800 --> 00:06:13,562 I think the figures in the book were a little bit better 90 00:06:13,562 --> 00:06:17,400 than this, but they were all based on these sketches. 91 00:06:17,400 --> 00:06:21,160 And then I have a couple of the hindbrain inputs. 92 00:06:21,160 --> 00:06:25,790 Most of the cranial nerves come in through the hindbrain. 93 00:06:25,790 --> 00:06:28,630 There are cranial nerves for the midbrain too, 94 00:06:28,630 --> 00:06:30,780 but they're motor output. 95 00:06:30,780 --> 00:06:34,970 The third and fourth nerves come out of the midbrain. 96 00:06:34,970 --> 00:06:37,680 But the midbrain became important in other ways. 97 00:06:37,680 --> 00:06:41,420 First of all, it got visual input, as we will see. 98 00:06:41,420 --> 00:06:44,440 Probably not the original visual inputs came there, 99 00:06:44,440 --> 00:06:51,570 but it also was a link between those forebrain structures, 100 00:06:51,570 --> 00:06:55,110 like olfaction, and the motor system, 101 00:06:55,110 --> 00:06:57,300 which was controlled by the lower brain 102 00:06:57,300 --> 00:07:00,080 stem and the spinal cord. 103 00:07:00,080 --> 00:07:02,270 All right. 104 00:07:02,270 --> 00:07:05,370 So let's talk about now the expansions that 105 00:07:05,370 --> 00:07:07,900 occurred with these specializations 106 00:07:07,900 --> 00:07:09,190 at the rostral end. 107 00:07:09,190 --> 00:07:11,200 So brain starts to evolve. 108 00:07:13,882 --> 00:07:16,980 The hindbrain expansions in the chordates 109 00:07:16,980 --> 00:07:20,380 resulted from the evolution of adaptive sensory and motor 110 00:07:20,380 --> 00:07:22,970 functions. 111 00:07:22,970 --> 00:07:28,670 What's an example of a hindbrain sense? 112 00:07:28,670 --> 00:07:31,150 Input that comes in through a cranial nerve 113 00:07:31,150 --> 00:07:35,690 into the hindbrain, important sensory modalities. 114 00:07:40,039 --> 00:07:40,955 What did we just show? 115 00:07:44,600 --> 00:07:45,995 What do those mean? 116 00:07:50,290 --> 00:07:52,860 So now the sensory will be talking 117 00:07:52,860 --> 00:07:57,850 about the trigeminal nerve [INAUDIBLE], the head region, 118 00:07:57,850 --> 00:07:59,360 especially the face. 119 00:07:59,360 --> 00:08:01,095 And then I have vestibular. 120 00:08:01,095 --> 00:08:04,710 I put vestibular in not auditory because vestibular 121 00:08:04,710 --> 00:08:05,690 is even more ancient. 122 00:08:12,590 --> 00:08:16,477 At least we think it is-- a lot of these things, 123 00:08:16,477 --> 00:08:18,060 there's a little bit of debate, and it 124 00:08:18,060 --> 00:08:21,210 depends on the details they find in the skulls. 125 00:08:21,210 --> 00:08:24,006 And it's been very difficult to get 126 00:08:24,006 --> 00:08:28,280 the very early period pinned down. 127 00:08:28,280 --> 00:08:30,160 And I've asked you-- there's a homework 128 00:08:30,160 --> 00:08:33,510 thing relevant to that, and you'll 129 00:08:33,510 --> 00:08:39,822 be looking on the internet for some of that data. 130 00:08:39,822 --> 00:08:43,440 So here now, I've taken that brain with the three brain 131 00:08:43,440 --> 00:08:46,500 vesicles, and I've showed and expanded hindbrain. 132 00:08:50,750 --> 00:08:53,540 And we should keep in mind that, of course, 133 00:08:53,540 --> 00:09:01,030 along with these specialized inputs coming in, 134 00:09:01,030 --> 00:09:06,150 the brain evolved action patterns, movement control, 135 00:09:06,150 --> 00:09:09,530 that was new too. 136 00:09:09,530 --> 00:09:12,780 When it's a genetically controlled, 137 00:09:12,780 --> 00:09:16,410 a genetic controlled development of a circuit controlling 138 00:09:16,410 --> 00:09:19,690 movement, we call it a fixed action pattern, 139 00:09:19,690 --> 00:09:23,730 or an instinctive movement pattern. 140 00:09:23,730 --> 00:09:26,740 That's a term from the ethologists, 141 00:09:26,740 --> 00:09:30,700 but we can apply it to our discussion of the brain. 142 00:09:34,420 --> 00:09:37,290 So let's now compare the specializations 143 00:09:37,290 --> 00:09:40,280 for case senses of a couple of fish, 144 00:09:40,280 --> 00:09:44,410 where this-- I like the illustrations from Herrick 145 00:09:44,410 --> 00:09:47,085 we're going to show. 146 00:09:47,085 --> 00:09:52,500 These are the Herrick brothers. 147 00:09:52,500 --> 00:09:56,270 Clarence Herrick and C. Judson Herrick were brothers, 148 00:09:56,270 --> 00:09:58,470 and they certainly helped establish 149 00:09:58,470 --> 00:10:02,580 the field of comparative neurology in America. 150 00:10:05,470 --> 00:10:08,610 That doesn't mean there wasn't similar kind of work being done 151 00:10:08,610 --> 00:10:12,830 in Europe and possibly elsewhere in the world, 152 00:10:12,830 --> 00:10:21,100 but they had these beautiful illustrations of fish. 153 00:10:21,100 --> 00:10:22,569 What is the sense? 154 00:10:22,569 --> 00:10:23,235 Do you remember? 155 00:10:23,235 --> 00:10:24,840 Did you read it? 156 00:10:24,840 --> 00:10:27,960 What's the sense that led to some 157 00:10:27,960 --> 00:10:31,750 of the marked expansions of the hindbrain? 158 00:10:31,750 --> 00:10:37,330 Not trigeminal, not vestibular, but something else. 159 00:10:40,855 --> 00:10:41,355 Taste. 160 00:10:43,860 --> 00:10:47,190 So these are to summarize the animals we're going to look at. 161 00:10:50,120 --> 00:10:53,610 I got the pictures from C. Judson Herrick's book, 162 00:10:53,610 --> 00:10:57,910 but they're actually all drawn originally by his brother. 163 00:10:57,910 --> 00:11:01,140 This one I take for comparison of the others. 164 00:11:01,140 --> 00:11:04,190 If you just look at this brain, the brain 165 00:11:04,190 --> 00:11:06,695 goes from this lower arrow all the way there 166 00:11:06,695 --> 00:11:13,900 to the olfactory bulbs, which are peduncle connecting 167 00:11:13,900 --> 00:11:16,875 the olfactory-- it looks like eyes, but they're not. 168 00:11:16,875 --> 00:11:20,400 This is all central nervous system. 169 00:11:20,400 --> 00:11:27,140 And the midbrain is actually the widest part. 170 00:11:27,140 --> 00:11:30,527 And behind it, between the arrows, is the hindbrain. 171 00:11:30,527 --> 00:11:35,000 Now, keep that in mind and look at these other fishes. 172 00:11:35,000 --> 00:11:35,990 This is the moon eye. 173 00:11:35,990 --> 00:11:39,140 Look at the buffalo fish. 174 00:11:39,140 --> 00:11:40,920 You look at this, and you're used 175 00:11:40,920 --> 00:11:42,810 to seeing pictures of human brain, 176 00:11:42,810 --> 00:11:45,380 and you see something like this, and what on earth 177 00:11:45,380 --> 00:11:46,400 are we looking at? 178 00:11:46,400 --> 00:11:53,310 Well, we're looking at changes in the neural tube, expansions 179 00:11:53,310 --> 00:11:57,560 for specialized sensory motor control. 180 00:11:57,560 --> 00:12:00,540 We call this in the buffalo fish, 181 00:12:00,540 --> 00:12:04,150 the vagal lobe because the input to it 182 00:12:04,150 --> 00:12:09,040 comes through the vagus nerve, the 10th cranial nerve. 183 00:12:09,040 --> 00:12:12,060 Now, the 10th cranial nerve in vertebrates 184 00:12:12,060 --> 00:12:20,830 generally carries sensory input from the viscera, 185 00:12:20,830 --> 00:12:24,905 but the visceral sensory neurons get that input. 186 00:12:24,905 --> 00:12:27,890 The rostral part gets taste input, 187 00:12:27,890 --> 00:12:31,280 coming from the throat, the palate 188 00:12:31,280 --> 00:12:33,110 and the sides of the throat. 189 00:12:37,950 --> 00:12:42,000 In humans, there's a little bit of taste input still coming. 190 00:12:42,000 --> 00:12:47,190 This animal has a specialized palatal organ. 191 00:12:47,190 --> 00:12:54,320 They filter-- they draw in little particles of the debris, 192 00:12:54,320 --> 00:12:58,210 the mud, at the bottom of lakes and rivers where they live, 193 00:12:58,210 --> 00:13:00,330 and they filter it. 194 00:13:00,330 --> 00:13:02,430 And they're basically tasting it. 195 00:13:02,430 --> 00:13:06,600 And there are specialized motor functions of that filtering 196 00:13:06,600 --> 00:13:10,150 apparatus as well, so they can select out 197 00:13:10,150 --> 00:13:11,840 the edible things in the water. 198 00:13:14,900 --> 00:13:19,142 And they don't need a whole lot of vision for that. 199 00:13:19,142 --> 00:13:23,990 They just lie near the bottom and do their feeding. 200 00:13:23,990 --> 00:13:26,820 OK, now here's another animal that you're probably 201 00:13:26,820 --> 00:13:28,130 more familiar with-- catfish. 202 00:13:31,190 --> 00:13:33,800 This would be like the bull-heads many children catch 203 00:13:33,800 --> 00:13:36,087 when they go fishing when they're kids, 204 00:13:36,087 --> 00:13:37,545 but there are many other catfishes. 205 00:13:40,120 --> 00:13:42,135 Again, strange-looking brain. 206 00:13:42,135 --> 00:13:44,780 But now the endbrains are a little bit bigger. 207 00:13:44,780 --> 00:13:47,120 They don't show the olfactory bulbs here, 208 00:13:47,120 --> 00:13:50,990 just the stalks that connect to them. 209 00:13:50,990 --> 00:13:54,180 And then you see the midbrain is still pretty wide. 210 00:13:54,180 --> 00:13:57,210 You didn't even see them. 211 00:13:57,210 --> 00:14:00,000 The midbrain here is not as distinct 212 00:14:00,000 --> 00:14:03,280 as it is in the mooneye. 213 00:14:03,280 --> 00:14:07,185 There's the big endbrain with the two tectal regions. 214 00:14:07,185 --> 00:14:08,870 There's the mooneye. 215 00:14:08,870 --> 00:14:10,135 Here's the catfish. 216 00:14:10,135 --> 00:14:13,900 The midbrain is bulging out quite a bit. 217 00:14:13,900 --> 00:14:18,320 But now all of this is cerebellum. 218 00:14:18,320 --> 00:14:20,840 So it's more specialized in the cerebellum. 219 00:14:20,840 --> 00:14:23,900 But I want you to look at these bulges behind, 220 00:14:23,900 --> 00:14:26,600 because they all get taste input. 221 00:14:26,600 --> 00:14:30,560 There's the vagal low, much smaller 222 00:14:30,560 --> 00:14:32,680 than in the buffalo fish. 223 00:14:32,680 --> 00:14:34,130 Here it is in the buffalo fish. 224 00:14:34,130 --> 00:14:36,260 Here it is in the catfish. 225 00:14:36,260 --> 00:14:40,146 But this bulge is called the facial lobe 226 00:14:40,146 --> 00:14:43,190 because that comes in through the seventh cranial nerve, 227 00:14:43,190 --> 00:14:47,690 and in this animal, much of it is carrying taste input. 228 00:14:51,360 --> 00:14:55,810 So let's look at their specialized taste system. 229 00:14:55,810 --> 00:14:57,860 There's a catfish. 230 00:14:57,860 --> 00:15:04,290 And this picture is illustrating just the seventh cranial nerve. 231 00:15:04,290 --> 00:15:08,250 It's a cranial nerve, and it is getting input from the head 232 00:15:08,250 --> 00:15:13,870 region, including input from these little marbles 233 00:15:13,870 --> 00:15:18,090 here that drags along the bottom as he's swimming. 234 00:15:18,090 --> 00:15:19,170 It's a taste organ. 235 00:15:23,450 --> 00:15:26,590 But what is all this? 236 00:15:26,590 --> 00:15:28,535 It's the seventh cranial nerve distributing 237 00:15:28,535 --> 00:15:31,700 over the body surface of most of this animal. 238 00:15:31,700 --> 00:15:37,282 He tastes with his body surface, everywhere on his body. 239 00:15:37,282 --> 00:15:39,690 And it's all innervated by a cranial nerve. 240 00:15:39,690 --> 00:15:42,830 So that seventh nerve is no longer 241 00:15:42,830 --> 00:15:47,540 just-- it's coming into the head region, into the hindbrain. 242 00:15:47,540 --> 00:15:50,020 But it's carrying taste input from all over the body. 243 00:15:52,760 --> 00:15:55,360 So again, this animal is not depending mainly 244 00:15:55,360 --> 00:16:00,670 on its eyes but feeding, but on its taste organs. 245 00:16:00,670 --> 00:16:03,116 And it's led to these enlargements. 246 00:16:03,116 --> 00:16:08,010 Now, that point, the specialized sensory functions, 247 00:16:08,010 --> 00:16:11,430 require neural processing power. 248 00:16:11,430 --> 00:16:16,880 And that entails enlargement of the neural apparatus 249 00:16:16,880 --> 00:16:18,365 that accomplishes it. 250 00:16:18,365 --> 00:16:19,980 So structures get bigger. 251 00:16:24,390 --> 00:16:26,310 So now let's go up to the forebrain 252 00:16:26,310 --> 00:16:29,920 and talk about what I call the first expansion 253 00:16:29,920 --> 00:16:31,710 of the forebrain in evolution. 254 00:16:31,710 --> 00:16:36,615 What caused the forebrain to start to enlarge? 255 00:16:39,780 --> 00:16:43,260 The olfactory system, we think, has certainly 256 00:16:43,260 --> 00:16:45,860 led to its expansion. 257 00:16:45,860 --> 00:16:48,800 There's other things happening in the forebrain, 258 00:16:48,800 --> 00:16:52,370 mentioning our secretory cells, the caudal end 259 00:16:52,370 --> 00:16:56,600 is also getting the visual inputs. 260 00:16:56,600 --> 00:17:00,800 But the first real expansion of the parts of the forebrain we 261 00:17:00,800 --> 00:17:05,228 call the endbrain, the forward part of the forebrain, 262 00:17:05,228 --> 00:17:07,690 is because of olfaction. 263 00:17:07,690 --> 00:17:10,839 And I just note here that when you see drawings, 264 00:17:10,839 --> 00:17:14,940 I'm often going to-- like, here I show pathways 265 00:17:14,940 --> 00:17:19,020 on one side here and another side here. 266 00:17:19,020 --> 00:17:21,990 Keep in mind that almost always, these pathways 267 00:17:21,990 --> 00:17:24,530 are on both sides. 268 00:17:24,530 --> 00:17:26,099 But if I draw them on both sides, 269 00:17:26,099 --> 00:17:28,590 the diagrams can get very complicated. 270 00:17:28,590 --> 00:17:31,289 So I often show them only on one side. 271 00:17:31,289 --> 00:17:33,580 But you have to keep that in mind throughout the class. 272 00:17:33,580 --> 00:17:36,735 We'll often show them only on one side. 273 00:17:36,735 --> 00:17:39,330 It makes it a lot clearer. 274 00:17:39,330 --> 00:17:43,390 So here you'll see olfactory bulbs and some 275 00:17:43,390 --> 00:17:45,375 of the connections of the olfactory bulb. 276 00:17:45,375 --> 00:17:51,560 They're coming in to more caudal parts of the forebrain. 277 00:17:51,560 --> 00:17:55,015 In this case, it's parts of the endbrain. 278 00:17:57,800 --> 00:18:00,205 They're not going clear back into that predecessor 279 00:18:00,205 --> 00:18:02,110 of hypothalamus. 280 00:18:02,110 --> 00:18:07,630 They're coming to a part that became the corpus striatum. 281 00:18:07,630 --> 00:18:10,980 In fact, it's the most primitive part of the corpus striatum. 282 00:18:10,980 --> 00:18:13,760 That area, the striatal areas, have 283 00:18:13,760 --> 00:18:18,400 outputs that control locomotion. 284 00:18:18,400 --> 00:18:21,040 How did it do that? 285 00:18:21,040 --> 00:18:24,085 Well, olfactory sense isn't doing the animal any good 286 00:18:24,085 --> 00:18:26,460 if it can't control his movements, 287 00:18:26,460 --> 00:18:29,980 and it controlled movements mainly 288 00:18:29,980 --> 00:18:33,800 by connections from the striatum that 289 00:18:33,800 --> 00:18:37,310 went from there into the midbrain. 290 00:18:37,310 --> 00:18:39,440 There were no connections to the spinal cord, 291 00:18:39,440 --> 00:18:41,050 no connections to the hindbrain. 292 00:18:41,050 --> 00:18:43,020 They were shorter connections, which 293 00:18:43,020 --> 00:18:46,280 is generally true in these primitive brains-- shorter 294 00:18:46,280 --> 00:18:47,360 connections. 295 00:18:47,360 --> 00:18:51,265 And here's an example of a striatal cell connecting 296 00:18:51,265 --> 00:18:53,855 to the midbrain, the caudal part of the midbrain. 297 00:18:53,855 --> 00:18:57,730 And there are neurons there that we know drive locomotive 298 00:18:57,730 --> 00:18:59,212 behavior. 299 00:18:59,212 --> 00:19:03,110 It's important even in humans. 300 00:19:03,110 --> 00:19:09,650 And then that area has outputs down to the hindbrain and even, 301 00:19:09,650 --> 00:19:11,920 in many animals, directly to the spinal cord. 302 00:19:16,016 --> 00:19:19,100 There was something special about that connection 303 00:19:19,100 --> 00:19:25,730 in the striatum that led to a property of the forebrain that 304 00:19:25,730 --> 00:19:28,670 is absolutely critical to its evolution. 305 00:19:28,670 --> 00:19:34,500 And that is this-- that the striatal connections 306 00:19:34,500 --> 00:19:36,690 were plastic. 307 00:19:36,690 --> 00:19:38,540 They could be strengthened or weakened, 308 00:19:38,540 --> 00:19:41,810 depending on the experience of the animal. 309 00:19:41,810 --> 00:19:43,760 So here's that animal foraging. 310 00:19:43,760 --> 00:19:49,690 He's smelling things, tasting things. 311 00:19:49,690 --> 00:19:55,760 He's getting feedback about the area he's swimming through. 312 00:19:55,760 --> 00:19:58,652 So he learns whether they're good or bad. 313 00:19:58,652 --> 00:20:01,560 He learns whether that's something worth approaching, 314 00:20:01,560 --> 00:20:03,340 or if it's dangerous. 315 00:20:08,720 --> 00:20:09,568 Sorry? 316 00:20:09,568 --> 00:20:10,484 AUDIENCE: [INAUDIBLE]. 317 00:20:15,360 --> 00:20:18,422 PROFESSOR: That's another issue about neurogenesis 318 00:20:18,422 --> 00:20:20,670 and its role in learning. 319 00:20:20,670 --> 00:20:25,940 We have areas important in learning. 320 00:20:25,940 --> 00:20:29,410 It's true that two major structures, the learning 321 00:20:29,410 --> 00:20:31,650 centers on them both have neurogenesis-- 322 00:20:31,650 --> 00:20:37,140 hippocampal formation and the olfactory bulbs. 323 00:20:37,140 --> 00:20:42,750 But in fact, the changes I'm talking about here 324 00:20:42,750 --> 00:20:45,130 are not an area of a lot of neurogenesis 325 00:20:45,130 --> 00:20:48,260 in the adult, the striatal areas. 326 00:20:48,260 --> 00:20:50,350 What you're talking about is happening 327 00:20:50,350 --> 00:20:54,420 in the tiny neurons right in the bulb. 328 00:20:54,420 --> 00:20:59,580 So don't connect learning necessarily with neurogenesis. 329 00:20:59,580 --> 00:21:03,630 But when I say they're plastic, there probably 330 00:21:03,630 --> 00:21:06,460 does entail actual morphological changes. 331 00:21:06,460 --> 00:21:07,930 Most forms of learning do. 332 00:21:13,670 --> 00:21:18,270 This was the predecessor to habit formation in the higher 333 00:21:18,270 --> 00:21:20,470 vertebrates, including us. 334 00:21:20,470 --> 00:21:23,070 The corpus striatum, which Ann Graybiel's 335 00:21:23,070 --> 00:21:24,950 been studying for many years, it's 336 00:21:24,950 --> 00:21:29,255 a very important site for habit formation. 337 00:21:31,890 --> 00:21:35,760 It's the reason that area has, like cortical areas, 338 00:21:35,760 --> 00:21:39,318 expanded in evolution. 339 00:21:39,318 --> 00:21:41,892 OK, let's go back to the midbrain now. 340 00:21:41,892 --> 00:21:43,836 I said, what structure in the midbrain 341 00:21:43,836 --> 00:21:50,154 has become greatly enlarged in most predatory TAS fish? 342 00:21:50,154 --> 00:21:53,070 And then I want to talk about the two 343 00:21:53,070 --> 00:21:56,362 major outputs of that structure. 344 00:21:56,362 --> 00:21:59,740 One descends and crosses the midline. 345 00:21:59,740 --> 00:22:02,287 The other has an uncrossed projection. 346 00:22:02,287 --> 00:22:04,036 So we've got another problem to deal with. 347 00:22:04,036 --> 00:22:06,481 Why do things cross at all? 348 00:22:06,481 --> 00:22:06,980 OK. 349 00:22:10,102 --> 00:22:13,140 What is the structure I'm thinking of? 350 00:22:13,140 --> 00:22:17,066 What's the big structure in predatory fish? 351 00:22:17,066 --> 00:22:21,430 When you look at the brain, it's really obvious. 352 00:22:21,430 --> 00:22:24,358 There it is. 353 00:22:24,358 --> 00:22:25,660 It's a visual sense. 354 00:22:25,660 --> 00:22:28,030 It's the surface gets visual input. 355 00:22:28,030 --> 00:22:29,310 It's the optic tectum. 356 00:22:29,310 --> 00:22:30,960 And there you see it. 357 00:22:30,960 --> 00:22:32,573 And this is a barracuda, an animal 358 00:22:32,573 --> 00:22:34,822 you've probably heard of because sports fishermen like 359 00:22:34,822 --> 00:22:36,735 to fish for the barracuda. 360 00:22:36,735 --> 00:22:40,540 But just look-- here's the olfactory bulbs-- not 361 00:22:40,540 --> 00:22:41,746 very visible. 362 00:22:41,746 --> 00:22:46,230 And when they remove the skull, they 363 00:22:46,230 --> 00:22:48,850 left some tissue around the olfactory bulb there. 364 00:22:48,850 --> 00:22:52,060 But there's the endbrain, which includes 365 00:22:52,060 --> 00:22:55,550 the corpus striatum and pallial structures. 366 00:22:55,550 --> 00:22:58,400 Because remember, it's still part of the neural tube. 367 00:22:58,400 --> 00:23:01,550 So it's a tube where the walls thicken, and there's 368 00:23:01,550 --> 00:23:03,196 fluid in the middle. 369 00:23:03,196 --> 00:23:05,750 And the part above that ventricle 370 00:23:05,750 --> 00:23:08,915 we call the pallium, or the cortex. 371 00:23:08,915 --> 00:23:15,932 And the part below, which often develops quite differently, 372 00:23:15,932 --> 00:23:19,496 is where the striatum develops in the endbrain. 373 00:23:19,496 --> 00:23:20,980 But there's the tectum. 374 00:23:23,540 --> 00:23:28,000 Here's a diagram that shows that its connection-- a connection 375 00:23:28,000 --> 00:23:31,040 that dominated in these predatory fish 376 00:23:31,040 --> 00:23:33,306 we're talking about-- a connection from the eye. 377 00:23:33,306 --> 00:23:36,540 And all of it comes from the opposite eye 378 00:23:36,540 --> 00:23:42,390 in lateral eyed animals, animals with eyes that sit out here. 379 00:23:42,390 --> 00:23:50,155 Even in the hamster, whose eyes look about 60 degrees out-- 380 00:23:50,155 --> 00:23:54,030 so there's some overlap in the visual field of the two eyes. 381 00:23:54,030 --> 00:23:57,982 They still have mostly a cross-projection like this. 382 00:23:57,982 --> 00:23:59,440 And it goes to the midbrain tectum. 383 00:24:02,070 --> 00:24:05,645 It allows an animal-- vision was so important, 384 00:24:05,645 --> 00:24:09,179 it led to marked changes in the brain. 385 00:24:09,179 --> 00:24:11,220 It was one of the two forebrain senses, olfaction 386 00:24:11,220 --> 00:24:15,670 and then vision-- because it gave something even better 387 00:24:15,670 --> 00:24:16,970 than olfaction did. 388 00:24:16,970 --> 00:24:19,110 Olfaction couldn't respond to things at a distance, 389 00:24:19,110 --> 00:24:21,830 but look at vision. 390 00:24:21,830 --> 00:24:23,480 It could get advanced warning. 391 00:24:23,480 --> 00:24:26,320 It could escape from things. 392 00:24:26,320 --> 00:24:31,650 It wasn't just predators that this was important for. 393 00:24:31,650 --> 00:24:35,870 And just another picture of it here. 394 00:24:35,870 --> 00:24:40,940 I point out that two major outputs 395 00:24:40,940 --> 00:24:43,570 that are so important in evolution, 396 00:24:43,570 --> 00:24:48,480 of that tectum of the midbrain. 397 00:24:48,480 --> 00:24:53,610 One of them controlled anti-predator behavior, 398 00:24:53,610 --> 00:24:55,242 turning away. 399 00:24:55,242 --> 00:24:59,370 And the same pathway not only controlled turning away, 400 00:24:59,370 --> 00:25:00,990 but it went to the locomotor system 401 00:25:00,990 --> 00:25:03,930 that I mentioned before-- that same region that 402 00:25:03,930 --> 00:25:07,115 was getting input indirectly through the striatum 403 00:25:07,115 --> 00:25:11,170 from the olfactory sense and triggered rapid locomotion. 404 00:25:11,170 --> 00:25:14,260 So now you have the means for the animal 405 00:25:14,260 --> 00:25:19,800 to respond by turning away and running, not just running, 406 00:25:19,800 --> 00:25:23,036 which could lead indirectly into the mouth of the predator. 407 00:25:23,036 --> 00:25:25,570 So he turns away and runs. 408 00:25:25,570 --> 00:25:26,990 But there was another pathway that 409 00:25:26,990 --> 00:25:30,200 developed as this projection gained 410 00:25:30,200 --> 00:25:34,500 a topographic organization, they developed the ability 411 00:25:34,500 --> 00:25:38,810 to turn towards things-- very important for finding food. 412 00:25:38,810 --> 00:25:44,310 And of course, for prey animals, for predators 413 00:25:44,310 --> 00:25:46,256 rather, it became particularly important. 414 00:25:46,256 --> 00:25:47,922 It's the only way they could catch prey, 415 00:25:47,922 --> 00:25:52,940 is if they had a highly evolved system through rapid orienting 416 00:25:52,940 --> 00:25:55,970 towards the prey. 417 00:25:55,970 --> 00:25:58,890 And this is the main structure for that early in evolution. 418 00:26:03,290 --> 00:26:05,170 So then here, this question-- why 419 00:26:05,170 --> 00:26:09,240 do the pathways from each eye to the midbrain cross 420 00:26:09,240 --> 00:26:10,920 to the opposite side like this? 421 00:26:10,920 --> 00:26:12,487 Why does that happen? 422 00:26:16,780 --> 00:26:18,986 I've never read a neuroanatomy book 423 00:26:18,986 --> 00:26:22,520 that actually has an explanation. 424 00:26:22,520 --> 00:26:25,350 But I have an explanation because I 425 00:26:25,350 --> 00:26:28,710 think it came from my study of sociobiology and animal 426 00:26:28,710 --> 00:26:29,330 behavior. 427 00:26:29,330 --> 00:26:32,820 I paid a lot of attention to evolution. 428 00:26:32,820 --> 00:26:36,590 The reason there's no explanation, even suggestions 429 00:26:36,590 --> 00:26:39,045 about why crossed pathways developed, 430 00:26:39,045 --> 00:26:43,225 it's because people weren't thinking in a Darwinian sense. 431 00:26:43,225 --> 00:26:46,670 They weren't thinking of Darwinian evolution. 432 00:26:46,670 --> 00:26:50,550 Anatomy developed within the field of medicine, 433 00:26:50,550 --> 00:26:54,825 and they were concerned with humans and comparisons 434 00:26:54,825 --> 00:26:56,580 with humans. 435 00:26:56,580 --> 00:26:58,210 So they weren't primarily thinking 436 00:26:58,210 --> 00:27:00,940 of Darwinian evolution. 437 00:27:00,940 --> 00:27:09,100 OK, I will just give you a very simple answer to this. 438 00:27:09,100 --> 00:27:11,100 We're going to go through it in more detail when 439 00:27:11,100 --> 00:27:13,495 we talk about the hindbrain, because it involves 440 00:27:13,495 --> 00:27:16,880 the somatosensory system as well. 441 00:27:16,880 --> 00:27:20,362 And this is just a little summary of the hypothesis, 442 00:27:20,362 --> 00:27:26,850 but to cut things short, they must have developed across 443 00:27:26,850 --> 00:27:30,820 pathway because it was more adaptive. 444 00:27:30,820 --> 00:27:35,590 It had to survive and reproduce in some way. 445 00:27:35,590 --> 00:27:41,740 So my proposal is, it allowed more rapid escape behavior. 446 00:27:44,610 --> 00:27:49,840 So without a synapse, they crossed-- 447 00:27:49,840 --> 00:27:54,300 contacted descending pathway that controls escape behavior. 448 00:27:54,300 --> 00:27:55,840 And that's the proposal that I would 449 00:27:55,840 --> 00:27:59,010 develop when we get to the hindbrain, 450 00:27:59,010 --> 00:28:02,090 when we will study how-- because it's not 451 00:28:02,090 --> 00:28:05,120 just the visual pathways that cross. 452 00:28:05,120 --> 00:28:08,700 It's the somatosensory pathways from our entire body 453 00:28:08,700 --> 00:28:10,650 are crossed. 454 00:28:10,650 --> 00:28:13,985 That's why everything controlling my right hand here 455 00:28:13,985 --> 00:28:19,320 is on the left side of my endbrain. 456 00:28:19,320 --> 00:28:21,225 I didn't say all of the brain. 457 00:28:21,225 --> 00:28:25,270 I said the endbrain, but also the midbrain. 458 00:28:25,270 --> 00:28:31,240 The midbrain and forebrain we have cross projections. 459 00:28:31,240 --> 00:28:33,810 Hindbrain and spinal cord, we don't. 460 00:28:38,200 --> 00:28:41,110 So now let's talk a little more about that expansion 461 00:28:41,110 --> 00:28:42,910 of the forebrain-- less likelihood 462 00:28:42,910 --> 00:28:46,140 have led to a second major expansion. 463 00:28:46,140 --> 00:28:48,540 It's already started to expand because 464 00:28:48,540 --> 00:28:52,630 of the importance of olfaction. 465 00:28:52,630 --> 00:28:57,325 Olfaction was so important in feeding and mating behavior, 466 00:28:57,325 --> 00:29:02,550 in knowing whether an animal was a male or a female, 467 00:29:02,550 --> 00:29:07,614 whether the female is receptive for mating. 468 00:29:07,614 --> 00:29:11,420 And so important in finding good food 469 00:29:11,420 --> 00:29:15,700 and discriminating it from bad food and doing so efficiently, 470 00:29:15,700 --> 00:29:18,988 not having to wait until you taste it. 471 00:29:18,988 --> 00:29:19,488 Yes? 472 00:29:23,930 --> 00:29:25,428 Speak up. 473 00:29:25,428 --> 00:29:26,344 AUDIENCE: [INAUDIBLE]. 474 00:29:51,700 --> 00:29:53,350 PROFESSOR: Sometimes they are. 475 00:29:53,350 --> 00:29:58,210 But in most cases, it's when certain genes 476 00:29:58,210 --> 00:30:03,660 will disappear from the population of genes. 477 00:30:03,660 --> 00:30:05,680 Those genes will disappear, and others 478 00:30:05,680 --> 00:30:10,190 will be preserved if there's any slight advantage. 479 00:30:10,190 --> 00:30:12,100 And for something like escape behavior, 480 00:30:12,100 --> 00:30:16,090 it only has to be small fractions of a second 481 00:30:16,090 --> 00:30:21,767 to make the difference between being caught and getting away. 482 00:30:21,767 --> 00:30:23,350 And it's because of that-- if you just 483 00:30:23,350 --> 00:30:26,740 watch the films on WGBH on escape 484 00:30:26,740 --> 00:30:30,290 behavior and predatory action and look at the high speed 485 00:30:30,290 --> 00:30:35,800 films they need, and you realize how split-second timing makes 486 00:30:35,800 --> 00:30:38,660 all the difference in survival. 487 00:30:38,660 --> 00:30:41,950 And that's what I'm basing this kind of thinking on. 488 00:30:41,950 --> 00:30:44,270 But we will bring this up again, and we'll 489 00:30:44,270 --> 00:30:46,380 talk a little more about it. 490 00:30:46,380 --> 00:30:48,790 I just want to give you an overview now of these brain 491 00:30:48,790 --> 00:30:51,420 expansions. 492 00:30:51,420 --> 00:30:55,460 The second major expansion-- another equally important. 493 00:30:55,460 --> 00:30:57,705 We had to have a forebrain already, 494 00:30:57,705 --> 00:30:59,930 and we know it must have been olfaction 495 00:30:59,930 --> 00:31:03,570 that led to its expansion. 496 00:31:03,570 --> 00:31:06,330 But we know now the forebrain is [INAUDIBLE] 497 00:31:06,330 --> 00:31:07,990 more than the olfactory system. 498 00:31:13,210 --> 00:31:17,090 Other senses came into the forebrain. 499 00:31:17,090 --> 00:31:19,800 I already mentioned the big advantage now 500 00:31:19,800 --> 00:31:22,350 to the olfactory connections to the striatum, 501 00:31:22,350 --> 00:31:25,070 they were plastic. 502 00:31:25,070 --> 00:31:28,370 The connections of the visual system to the midbrain, 503 00:31:28,370 --> 00:31:31,710 as big as it was, were they plastic? 504 00:31:31,710 --> 00:31:32,960 Not in the same sense. 505 00:31:32,960 --> 00:31:37,250 Their short-term plasticity, habituation, sensitization, 506 00:31:37,250 --> 00:31:39,260 it doesn't last very long. 507 00:31:39,260 --> 00:31:41,745 But the kind of learning allowed habits 508 00:31:41,745 --> 00:31:45,180 to form, long-lasting habits. 509 00:31:45,180 --> 00:31:52,200 The other senses, I think, in evolution started coming into, 510 00:31:52,200 --> 00:31:56,000 invading the endbrain for that to take 511 00:31:56,000 --> 00:31:57,225 advantage of that system. 512 00:31:57,225 --> 00:31:59,430 They come directly to the striatum. 513 00:32:02,960 --> 00:32:06,310 There are visual path-- and most of them come this way. 514 00:32:06,310 --> 00:32:08,900 Here's a link in the midbrain. 515 00:32:08,900 --> 00:32:16,600 It's growing to neurons in what we call the tweenbrain. 516 00:32:16,600 --> 00:32:19,320 Most of them don't go directly from midbrain. 517 00:32:19,320 --> 00:32:23,750 Almost always, they'll go through the link there. 518 00:32:23,750 --> 00:32:27,770 And these then go into the endbrain-- 519 00:32:27,770 --> 00:32:31,080 the striatum but also the pallium. 520 00:32:34,080 --> 00:32:36,340 Let's just talk about the striatal ones, 521 00:32:36,340 --> 00:32:38,670 because that's the ones we've talked about already. 522 00:32:42,680 --> 00:32:46,470 There's great advantages to be able to learn and remember 523 00:32:46,470 --> 00:32:50,600 habits based on visual input and auditory 524 00:32:50,600 --> 00:32:54,840 and taste input-- so input coming 525 00:32:54,840 --> 00:32:58,780 from more caudal structures. 526 00:32:58,780 --> 00:33:01,110 Now, the visual input, some of that 527 00:33:01,110 --> 00:33:04,690 came directly into the tweenbrain. 528 00:33:04,690 --> 00:33:07,910 The eyes actually involved from the tweenbrain. 529 00:33:07,910 --> 00:33:10,700 So this pathway I'm showing from the midbrain certainly 530 00:33:10,700 --> 00:33:13,931 wasn't the only one carrying visual information 531 00:33:13,931 --> 00:33:17,080 into the striatum. 532 00:33:17,080 --> 00:33:19,277 Some visual input went right through a part 533 00:33:19,277 --> 00:33:20,110 of the diencephelon. 534 00:33:20,110 --> 00:33:23,990 We called it the subthalamus, which projects directly 535 00:33:23,990 --> 00:33:30,770 to the striatum, as does the older parts of the thalamus. 536 00:33:30,770 --> 00:33:31,460 All right. 537 00:33:31,460 --> 00:33:33,620 So I think that's what led to the second expansion. 538 00:33:37,330 --> 00:33:40,740 Then I say a third major expansion of the forebrain 539 00:33:40,740 --> 00:33:43,359 has occurred in mammals, apparently 540 00:33:43,359 --> 00:33:45,275 because of the evolution of another structure. 541 00:33:47,860 --> 00:33:50,680 You should all know what that is. 542 00:33:50,680 --> 00:33:56,050 What is the huge part of the human brain? 543 00:33:56,050 --> 00:33:57,910 The neocortex. 544 00:33:57,910 --> 00:34:06,020 And what in a thumbnail here does it do? 545 00:34:06,020 --> 00:34:08,009 I'm mentioning here the various functions 546 00:34:08,009 --> 00:34:12,286 that led to these changes in the neural tube. 547 00:34:12,286 --> 00:34:15,295 But the one that involves neocortex 548 00:34:15,295 --> 00:34:19,380 is this last one, systems for anticipating events 549 00:34:19,380 --> 00:34:26,239 and planning actions, the things we call the cognitive systems. 550 00:34:26,239 --> 00:34:28,449 I'm not going to mention communication, language, 551 00:34:28,449 --> 00:34:29,150 and all of that. 552 00:34:29,150 --> 00:34:33,920 That was a very specialized things that happened in humans. 553 00:34:33,920 --> 00:34:35,890 This is mammals in general. 554 00:34:39,940 --> 00:34:45,489 And I'm describing here those systems 555 00:34:45,489 --> 00:34:47,650 for anticipating things. 556 00:34:47,650 --> 00:34:50,649 We call on the sensory side, sensory images. 557 00:34:50,649 --> 00:34:52,184 And I use that very broadly. 558 00:34:52,184 --> 00:34:55,883 We have auditory images, visual images, 559 00:34:55,883 --> 00:34:59,295 some of the sensory images, and for planning and preparing 560 00:34:59,295 --> 00:35:03,581 for actions-- all non-reflex types of functions involving 561 00:35:03,581 --> 00:35:05,081 some kind of internal representation 562 00:35:05,081 --> 00:35:07,787 of the external role. 563 00:35:07,787 --> 00:35:14,000 That's what the neocortex is specialized for. 564 00:35:14,000 --> 00:35:16,880 And I hear mention, something you'll hear a number of times 565 00:35:16,880 --> 00:35:20,590 in the class, that yes, some animals don't have 566 00:35:20,590 --> 00:35:24,615 very much like a neocortex, like the birds. 567 00:35:24,615 --> 00:35:26,430 But there are non-neocortex structures 568 00:35:26,430 --> 00:35:30,370 that accomplish similar functions, because they 569 00:35:30,370 --> 00:35:33,285 have connections like the neocortex. 570 00:35:33,285 --> 00:35:36,003 So we'll be encountering that and discussing 571 00:35:36,003 --> 00:35:40,186 that a little bit as the class goes on. 572 00:35:40,186 --> 00:35:42,510 So this was a third major expansion. 573 00:35:42,510 --> 00:35:45,750 And it was the neocortex that expanded, 574 00:35:45,750 --> 00:35:48,180 especially-- I just mentioned here-- 575 00:35:48,180 --> 00:35:52,260 the part in the higher animals, especially 576 00:35:52,260 --> 00:35:54,170 the primates but other animals too 577 00:35:54,170 --> 00:35:57,630 that expanded the most, certainly in primates, 578 00:35:57,630 --> 00:36:00,615 was what we call the association cortex. 579 00:36:00,615 --> 00:36:02,610 And I develop the idea in the book 580 00:36:02,610 --> 00:36:06,110 that that association cortex that's 581 00:36:06,110 --> 00:36:08,930 expanded the most in more recent evolution 582 00:36:08,930 --> 00:36:14,310 is actually-- it has properties like the earliest 583 00:36:14,310 --> 00:36:19,770 cortex, the earliest pallium, not the most specialized cortex 584 00:36:19,770 --> 00:36:21,290 that evolved in between. 585 00:36:24,720 --> 00:36:25,270 OK. 586 00:36:25,270 --> 00:36:30,130 But you'll see my reason for that as we go on. 587 00:36:30,130 --> 00:36:31,945 And of course, as the cortex expanded, 588 00:36:31,945 --> 00:36:35,270 the cortex projects to everything-- projects 589 00:36:35,270 --> 00:36:37,150 heavily to the corpus striatum that 590 00:36:37,150 --> 00:36:41,340 led to the expansion of the striatum that projects 591 00:36:41,340 --> 00:36:45,730 to the cerebellum, and led to expansions of the cerebellum. 592 00:36:45,730 --> 00:36:47,005 So here I just depict that. 593 00:36:47,005 --> 00:36:50,530 I take this primitive animal with a somewhat expanded 594 00:36:50,530 --> 00:36:55,300 forebrain, a pretty big midbrain. 595 00:36:55,300 --> 00:36:59,765 And I show how that endbrain grew. 596 00:36:59,765 --> 00:37:01,620 It grew a lot. 597 00:37:01,620 --> 00:37:05,980 And this would be like a rodent that we study in the lab. 598 00:37:05,980 --> 00:37:09,420 And along with that, the cerebellum expanded. 599 00:37:09,420 --> 00:37:11,610 And it's a correlation that's pretty strong. 600 00:37:14,280 --> 00:37:19,652 The bigger that forebrain gets, the bigger the neocortex gets, 601 00:37:19,652 --> 00:37:21,313 the bigger the cerebellum gets. 602 00:37:26,880 --> 00:37:28,830 And I had mentioned other functions here 603 00:37:28,830 --> 00:37:31,570 that I've not talked much about, controlling fine 604 00:37:31,570 --> 00:37:36,420 movements, especially with the evolution of distal appendages, 605 00:37:36,420 --> 00:37:41,660 the hands, the feet-- especially the hands can manipulate. 606 00:37:41,660 --> 00:37:45,420 That led to an evolution of one of these somatosensory areas 607 00:37:45,420 --> 00:37:49,380 that we started calling motor cortex as well 608 00:37:49,380 --> 00:37:51,105 as the cerebellar hemispheres. 609 00:37:51,105 --> 00:37:54,190 But the cerebellum gets input from all different areas 610 00:37:54,190 --> 00:37:58,490 of cortex, including the association areas. 611 00:37:58,490 --> 00:38:01,280 So let's just talk-- we talked about expansions. 612 00:38:01,280 --> 00:38:03,630 Let's just talk a little bit about methods 613 00:38:03,630 --> 00:38:07,986 for comparing brain size in the various major groupings 614 00:38:07,986 --> 00:38:12,800 of chordates and talk about a major result 615 00:38:12,800 --> 00:38:14,070 of such comparisons. 616 00:38:14,070 --> 00:38:17,080 What is the method I'm thinking of? 617 00:38:17,080 --> 00:38:18,066 Yes. 618 00:38:18,066 --> 00:38:18,982 AUDIENCE: [INAUDIBLE]. 619 00:38:22,780 --> 00:38:24,550 PROFESSOR: Yes. 620 00:38:24,550 --> 00:38:27,000 We almost always will take the ratio. 621 00:38:27,000 --> 00:38:29,100 We talk about relative brain size, 622 00:38:29,100 --> 00:38:33,500 because we're comparing it to body weight. 623 00:38:33,500 --> 00:38:35,860 That's because the size of the body 624 00:38:35,860 --> 00:38:39,140 is such a major determinant of the size of the brain. 625 00:38:42,220 --> 00:38:45,742 Now, there are exceptions for individual structures, 626 00:38:45,742 --> 00:38:51,758 but in general, as body size expands, so does the brain. 627 00:38:51,758 --> 00:38:58,580 And you plot brainwave versus body weight, 628 00:38:58,580 --> 00:39:05,780 and it usually is done on log-log scales, like here. 629 00:39:05,780 --> 00:39:07,130 Not showing individual points. 630 00:39:07,130 --> 00:39:08,450 Here's a point for mammals. 631 00:39:08,450 --> 00:39:14,750 You can see they plotted here on the ordinate, the size 632 00:39:14,750 --> 00:39:17,275 of the brain, and they plot the body size here. 633 00:39:17,275 --> 00:39:18,820 Here's the previous one. 634 00:39:18,820 --> 00:39:22,350 Here's the body weight in grams in logarithmic scale. 635 00:39:22,350 --> 00:39:24,430 Here's the brain weight in grams. 636 00:39:24,430 --> 00:39:29,470 And of course you can take volume just as well. 637 00:39:29,470 --> 00:39:35,505 And here, the different colors show the envelope 638 00:39:35,505 --> 00:39:39,810 of points for many different species of mammal. 639 00:39:39,810 --> 00:39:41,510 They're all in that green area. 640 00:39:44,140 --> 00:39:48,690 And here, the purple area down below, it's lower in general. 641 00:39:48,690 --> 00:39:52,630 But it still is along this diagonal line. 642 00:39:52,630 --> 00:39:55,405 That's the cartilaginous fishes, the sharks and the whales. 643 00:39:58,490 --> 00:40:05,140 And here, the upper part that's getting close to mammals, 644 00:40:05,140 --> 00:40:06,330 but a little bit below. 645 00:40:06,330 --> 00:40:07,076 It's the birds. 646 00:40:10,980 --> 00:40:16,340 And then this is a very large group, the ray-finned fishes 647 00:40:16,340 --> 00:40:26,040 that some of those are-- it's almost reached the birds here. 648 00:40:26,040 --> 00:40:30,560 And even just a little bit of overlap with some mammals. 649 00:40:30,560 --> 00:40:32,700 And then reptiles. 650 00:40:32,700 --> 00:40:36,040 And the lowest here are the jaw-less vertebrates. 651 00:40:39,370 --> 00:40:41,600 But again, a lot of overlap with that huge group 652 00:40:41,600 --> 00:40:44,210 of ray-finned fishes. 653 00:40:44,210 --> 00:40:48,400 And this is just for mammals-- and this one-- 654 00:40:48,400 --> 00:40:51,460 just a few points done to emphasize in blue, 655 00:40:51,460 --> 00:40:53,450 they're showing individual primates. 656 00:40:56,480 --> 00:40:58,740 And they've selected a few other animals, 657 00:40:58,740 --> 00:41:04,010 like porpoise because it has, in relative terms, a very 658 00:41:04,010 --> 00:41:07,410 large brain with respect to its body weight. 659 00:41:07,410 --> 00:41:12,890 But if I tell you that humans have relatively the largest 660 00:41:12,890 --> 00:41:21,292 brain, it's because the point is the farthest from that line. 661 00:41:21,292 --> 00:41:24,490 So relative size diminishes as we 662 00:41:24,490 --> 00:41:27,950 go in this direction and increases 663 00:41:27,950 --> 00:41:31,700 when we go in that direction. 664 00:41:31,700 --> 00:41:34,740 That's how you read those graphs. 665 00:41:34,740 --> 00:41:37,390 So you can see here, the animal with the largest 666 00:41:37,390 --> 00:41:42,740 brain of all living creatures, the blue whale. 667 00:41:42,740 --> 00:41:44,141 There he is. 668 00:41:44,141 --> 00:41:48,640 There's the elephant, also larger by far than human. 669 00:41:48,640 --> 00:41:51,490 But in relative terms, not as large. 670 00:41:54,570 --> 00:41:55,490 So that's the method. 671 00:42:06,530 --> 00:42:10,740 I would like to-- in a few minutes, 672 00:42:10,740 --> 00:42:13,190 because I've got a lot of slides for the next class-- I 673 00:42:13,190 --> 00:42:15,390 want to start discussing it now. 674 00:42:15,390 --> 00:42:19,610 We've already mentioned maybe a few things. 675 00:42:19,610 --> 00:42:21,930 You talked about development a minute ago 676 00:42:21,930 --> 00:42:24,800 and wanted to related it to giving us 677 00:42:24,800 --> 00:42:28,760 some evidence about brain expansion, brain 678 00:42:28,760 --> 00:42:30,200 change in evolution. 679 00:42:30,200 --> 00:42:32,620 There's been a lot made of that issue. 680 00:42:32,620 --> 00:42:35,430 You'll hear the phrase that ontogeny 681 00:42:35,430 --> 00:42:37,450 recapitulates biologically. 682 00:42:37,450 --> 00:42:39,460 What does that mean? 683 00:42:39,460 --> 00:42:40,740 What do the terms mean? 684 00:42:43,700 --> 00:42:46,640 And what do we mean by a phylotypic stage 685 00:42:46,640 --> 00:42:49,570 of development? 686 00:42:49,570 --> 00:42:54,470 This has been very popular in the earlier 687 00:42:54,470 --> 00:42:55,550 history of neuroscience. 688 00:43:00,890 --> 00:43:04,390 It's based on this kind of picture. 689 00:43:04,390 --> 00:43:09,040 This was drawn not by the original discoverer 690 00:43:09,040 --> 00:43:12,890 of the relationship which is by von Baer, 691 00:43:12,890 --> 00:43:15,426 a contemporary of Darwin. 692 00:43:15,426 --> 00:43:19,840 In fact, Darwin cites the idea in his book 693 00:43:19,840 --> 00:43:21,140 The Origin of Species. 694 00:43:21,140 --> 00:43:26,415 But I looked for it and found out he doesn't cite von Baer. 695 00:43:26,415 --> 00:43:30,380 He cites Louis Agassiz improperly. 696 00:43:33,720 --> 00:43:38,910 But Ernst Haeckel took up that idea a little later 697 00:43:38,910 --> 00:43:44,550 and did studies and came up with these pictures. 698 00:43:44,550 --> 00:43:46,360 He's taking these species you see 699 00:43:46,360 --> 00:43:49,470 at the bottom-- human, rabbit, cat, hog, chick, tortoise, 700 00:43:49,470 --> 00:43:56,720 salamander, and fish-- all looking very different 701 00:43:56,720 --> 00:43:59,390 in many details, anyway, when they're born. 702 00:43:59,390 --> 00:44:02,725 But look at them very early in development. 703 00:44:05,430 --> 00:44:07,720 This is after gastrulation. 704 00:44:07,720 --> 00:44:10,840 This is well after neurolation. 705 00:44:10,840 --> 00:44:14,906 And they're looking pretty similar. 706 00:44:14,906 --> 00:44:18,222 The only trouble was that Haeckel 707 00:44:18,222 --> 00:44:21,140 didn't look at every species. 708 00:44:21,140 --> 00:44:26,575 And sometimes he wasn't very accurate in the way 709 00:44:26,575 --> 00:44:28,030 he drew things. 710 00:44:28,030 --> 00:44:32,300 So it's still a relationship. 711 00:44:32,300 --> 00:44:34,160 Haeckel took it to extremes. 712 00:44:34,160 --> 00:44:35,970 This is the way he shows it-- very 713 00:44:35,970 --> 00:44:38,220 different in the early gastrula stages. 714 00:44:38,220 --> 00:44:41,090 Then he said if they were a member of the same phylum, 715 00:44:41,090 --> 00:44:43,720 like the chordates, they all went through a stage 716 00:44:43,720 --> 00:44:45,656 where they look like this. 717 00:44:45,656 --> 00:44:47,030 And then they develop differently 718 00:44:47,030 --> 00:44:50,495 into different species after that. 719 00:44:50,495 --> 00:44:52,660 And these were the pictures he drew just 720 00:44:52,660 --> 00:44:56,016 to illustrate the data for that. 721 00:44:56,016 --> 00:45:01,610 So even though there are really marked exceptions to it, 722 00:45:01,610 --> 00:45:03,430 the general relationship certainly 723 00:45:03,430 --> 00:45:06,950 leads you to believe that if you look 724 00:45:06,950 --> 00:45:09,030 at the nervous system in these early stages, 725 00:45:09,030 --> 00:45:14,360 they do look pretty similar in widely different chordates, 726 00:45:14,360 --> 00:45:16,220 even though they end up involving quite 727 00:45:16,220 --> 00:45:19,450 differently in different species. 728 00:45:19,450 --> 00:45:21,590 All right. 729 00:45:21,590 --> 00:45:24,610 So it leads us to at least expect many similarities 730 00:45:24,610 --> 00:45:26,850 in the CNS of all the vertebrates anyway. 731 00:45:26,850 --> 00:45:28,550 And these have been found. 732 00:45:31,990 --> 00:45:34,090 I've mentioned cynodonts already. 733 00:45:34,090 --> 00:45:35,892 What is a cynodont? 734 00:45:35,892 --> 00:45:40,490 Why is it important in the story of brain evolution? 735 00:45:40,490 --> 00:45:42,780 Why do I bring it up? 736 00:45:42,780 --> 00:45:44,620 Cynodonts have been extinct for some time. 737 00:45:50,740 --> 00:45:52,890 What is a cynodont? 738 00:45:52,890 --> 00:45:55,680 They existed for a very long period. 739 00:46:00,030 --> 00:46:02,264 They precede most-- sorry? 740 00:46:02,264 --> 00:46:03,180 AUDIENCE: [INAUDIBLE]. 741 00:46:06,930 --> 00:46:08,780 PROFESSOR: No, they're not dinosaurs. 742 00:46:08,780 --> 00:46:12,720 But they overlap with the dinosaurs. 743 00:46:12,720 --> 00:46:15,960 They did exist throughout the entire Jurassic period, 744 00:46:15,960 --> 00:46:19,200 but earlier. 745 00:46:19,200 --> 00:46:23,470 They existed through for geologic eras. 746 00:46:23,470 --> 00:46:24,375 Yes? 747 00:46:24,375 --> 00:46:26,800 AUDIENCE: [INAUDIBLE]. 748 00:46:26,800 --> 00:46:29,340 PROFESSOR: Exactly. 749 00:46:29,340 --> 00:46:32,990 The mammal-like reptiles is the more general way 750 00:46:32,990 --> 00:46:34,280 we refer to them. 751 00:46:34,280 --> 00:46:37,623 These are the mammal-like reptiles. 752 00:46:37,623 --> 00:46:41,840 But yes, mammals appeared and evolved 753 00:46:41,840 --> 00:46:47,740 during the period of the dinosaurs as little creatures, 754 00:46:47,740 --> 00:46:50,570 running around the forest floor. 755 00:46:50,570 --> 00:46:54,280 It was to their great advantage to be nocturnal, 756 00:46:54,280 --> 00:46:57,800 because so many dinosaurs were diurnal and had 757 00:46:57,800 --> 00:46:59,110 very good vision. 758 00:46:59,110 --> 00:47:03,360 So to avoid predation by those big reptiles, 759 00:47:03,360 --> 00:47:08,380 they had to occupy a different environmental niche. 760 00:47:08,380 --> 00:47:12,300 And it was among the cynodonts that we 761 00:47:12,300 --> 00:47:14,490 could say that the sketches I'm going to use 762 00:47:14,490 --> 00:47:18,570 were like an early cynodont, because the later cynodonts 763 00:47:18,570 --> 00:47:21,275 were really very similar in many ways to reptiles. 764 00:47:21,275 --> 00:47:26,780 But skull features show them still not to be mammals. 765 00:47:26,780 --> 00:47:29,160 And they go by a number of different features 766 00:47:29,160 --> 00:47:34,750 to specify how mammal-like they are. 767 00:47:40,010 --> 00:47:43,050 OK, well, we'll come back to this next time. 768 00:47:43,050 --> 00:47:46,660 And we'll be talking about what I 769 00:47:46,660 --> 00:47:49,840 think is like a cynodont brain, but you could also call it, 770 00:47:49,840 --> 00:47:52,596 like, an amphibian brain. 771 00:47:52,596 --> 00:47:55,500 The sketch would fit either one.