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 00:00:23,007 --> 00:00:24,590 PROFESSOR: And we didn't quite finish, 9 00:00:24,590 --> 00:00:30,030 last time, the last part of the visual system. 10 00:00:30,030 --> 00:00:32,850 So let me say a little bit about the transcortical connections. 11 00:00:36,390 --> 00:00:39,340 So what does it mean, this first statement? 12 00:00:39,340 --> 00:00:43,570 As neocortical area and neuron number increase in evolution, 13 00:00:43,570 --> 00:00:47,570 the amount of white matter increases also 14 00:00:47,570 --> 00:00:51,790 at a slightly greater rate. 15 00:00:51,790 --> 00:00:55,430 So what does that indicate? 16 00:00:55,430 --> 00:00:57,966 That would be one at issue to talk about. 17 00:01:02,660 --> 00:01:06,790 In the visual system, there are specific long transcortical 18 00:01:06,790 --> 00:01:11,240 connections that have been emphasized 19 00:01:11,240 --> 00:01:15,140 in recent neuropsychology, because they 20 00:01:15,140 --> 00:01:17,670 seem to be very important in understanding some 21 00:01:17,670 --> 00:01:21,040 of the functions of the neocortex. 22 00:01:21,040 --> 00:01:32,380 So I talk about three transcortical pathways 23 00:01:32,380 --> 00:01:35,410 in the chapter. 24 00:01:35,410 --> 00:01:37,830 Two of them are frequently talked 25 00:01:37,830 --> 00:01:39,920 about by cognitive neuroscientists. 26 00:01:45,880 --> 00:01:48,690 One of them is not so commonly talked about. 27 00:01:48,690 --> 00:01:54,840 But I have come to believe it's just as important. 28 00:01:54,840 --> 00:01:56,895 So I want to just quickly go through all three. 29 00:02:00,100 --> 00:02:02,270 Can any of you summarize for me what 30 00:02:02,270 --> 00:02:04,940 the main functions of these three pathways is? 31 00:02:04,940 --> 00:02:05,772 Yes? 32 00:02:05,772 --> 00:02:06,688 AUDIENCE: [INAUDIBLE]. 33 00:02:13,400 --> 00:02:15,322 PROFESSOR: Object location, that's right. 34 00:02:15,322 --> 00:02:16,238 AUDIENCE: [INAUDIBLE]. 35 00:02:23,830 --> 00:02:25,570 PROFESSOR: Yeah, effective associations 36 00:02:25,570 --> 00:02:26,710 is a good way to say it. 37 00:02:26,710 --> 00:02:32,020 But I think in terms of cognitive psychology, 38 00:02:32,020 --> 00:02:35,270 they would say identification of objects. 39 00:02:35,270 --> 00:02:37,950 Because to make an association, you have to know what it is. 40 00:02:37,950 --> 00:02:39,740 So if you encounter it again and you 41 00:02:39,740 --> 00:02:43,000 form that kind of affective association, 42 00:02:43,000 --> 00:02:44,800 you retain that knowledge. 43 00:02:44,800 --> 00:02:46,540 So that's right. 44 00:02:46,540 --> 00:02:47,726 What about the third one? 45 00:02:47,726 --> 00:02:48,642 AUDIENCE: [INAUDIBLE]. 46 00:02:51,408 --> 00:02:53,070 PROFESSOR: Yeah, I summarize it as, 47 00:02:53,070 --> 00:02:54,830 where am I. Now let me just-- 48 00:02:54,830 --> 00:02:55,800 AUDIENCE: [INAUDIBLE]. 49 00:02:55,800 --> 00:02:58,690 PROFESSOR: --let me explain. 50 00:02:58,690 --> 00:03:00,410 Without even looking at these slides, 51 00:03:00,410 --> 00:03:06,080 if I just-- when we talk about spatial location, 52 00:03:06,080 --> 00:03:09,440 we can mean where something is around our head. 53 00:03:12,095 --> 00:03:14,760 If I'm looking here, the clock is over there, 54 00:03:14,760 --> 00:03:16,430 in my left visual field. 55 00:03:16,430 --> 00:03:18,635 The windows are in my right visual field. 56 00:03:18,635 --> 00:03:20,480 The computer's in my central field, 57 00:03:20,480 --> 00:03:24,040 right now slightly in the lower field. 58 00:03:24,040 --> 00:03:26,910 This is all object location. 59 00:03:26,910 --> 00:03:31,870 We call it egocentric localization. 60 00:03:31,870 --> 00:03:35,010 That is, not with respect to the ego, 61 00:03:35,010 --> 00:03:39,810 with respect to our head-- head and eyes. 62 00:03:39,810 --> 00:03:42,680 OK, that's egocentric location. 63 00:03:42,680 --> 00:03:44,280 So what is allocentric? 64 00:03:44,280 --> 00:03:46,740 "Allo" means other. 65 00:03:46,740 --> 00:03:50,890 So my allocentric orientation is where 66 00:03:50,890 --> 00:03:53,910 I am in this room, where I am in the building, where 67 00:03:53,910 --> 00:03:55,552 I am at MIT. 68 00:03:55,552 --> 00:03:56,510 That's all allocentric. 69 00:03:59,750 --> 00:04:02,410 We'll talk about that when we look at the pathway 70 00:04:02,410 --> 00:04:03,730 to see what's involved in that. 71 00:04:03,730 --> 00:04:08,420 And it will come up a number of times again. 72 00:04:08,420 --> 00:04:12,440 It's becomes so important for understanding 73 00:04:12,440 --> 00:04:14,675 the medial pallium, the hippocampal formation 74 00:04:14,675 --> 00:04:19,760 and associated structures, in the last 15, 20 years. 75 00:04:22,520 --> 00:04:27,750 All right, this is often called the dorsal stream, 76 00:04:27,750 --> 00:04:31,480 leading from striate cortex, the first visual area. 77 00:04:35,430 --> 00:04:37,190 I put in a couple of arrows here. 78 00:04:37,190 --> 00:04:38,830 But I could have put in one big one. 79 00:04:38,830 --> 00:04:46,340 But they basically-- from all over area 17, visual area one, 80 00:04:46,340 --> 00:04:55,690 you get fibers projecting to juxtastriate areas, V2 81 00:04:55,690 --> 00:04:57,200 primarily. 82 00:04:57,200 --> 00:04:59,700 And from there, there are pathways 83 00:04:59,700 --> 00:05:01,840 that go to a number of places. 84 00:05:01,840 --> 00:05:05,580 And one of the places they go to is the posterior parietal area. 85 00:05:05,580 --> 00:05:11,350 And I've drawn here origins of several major bundles of axons 86 00:05:11,350 --> 00:05:15,360 that lead from the posterior parietal area 87 00:05:15,360 --> 00:05:17,240 into the prefrontal cortex. 88 00:05:17,240 --> 00:05:19,770 Now that posterior parietal area is 89 00:05:19,770 --> 00:05:23,980 concerned with spatial localization of things 90 00:05:23,980 --> 00:05:28,270 that we see around us. 91 00:05:28,270 --> 00:05:32,900 All right, so this is often called the ventral stream 92 00:05:32,900 --> 00:05:36,050 pathway, also originating in area 17, 93 00:05:36,050 --> 00:05:40,945 also projecting to the prestriate, the V2 areas. 94 00:05:44,210 --> 00:05:49,300 And from those areas in V2 and from 95 00:05:49,300 --> 00:05:53,460 the posterior parietal areas that are getting input 96 00:05:53,460 --> 00:05:55,410 from the prestriate areas, you have 97 00:05:55,410 --> 00:05:57,790 pathways leading into the temporal lobe, that part 98 00:05:57,790 --> 00:06:00,780 of the visual cortex that's expanded 99 00:06:00,780 --> 00:06:05,740 so much in the temporalization of the hemispheres. 100 00:06:05,740 --> 00:06:07,640 And so I've just sketched it here, 101 00:06:07,640 --> 00:06:15,680 indicating that they come from the areas bordering area 17, 102 00:06:15,680 --> 00:06:19,530 from a number of different visual areas there. 103 00:06:19,530 --> 00:06:22,685 And they project to the inferior temporal cortex, 104 00:06:22,685 --> 00:06:27,360 the inferior gyrus of the temporal lobe. 105 00:06:27,360 --> 00:06:30,310 And then for each of these pathways 106 00:06:30,310 --> 00:06:34,150 you can see there are pathways leading to the prefrontal. 107 00:06:34,150 --> 00:06:39,156 Here I show the dorsal pathways. 108 00:06:39,156 --> 00:06:41,840 I'll show you many other transcortical pathways 109 00:06:41,840 --> 00:06:42,910 in the monkey later. 110 00:06:42,910 --> 00:06:47,570 And they become confirmed, just about every one 111 00:06:47,570 --> 00:06:51,170 of them they know has a corresponding pathway 112 00:06:51,170 --> 00:06:51,670 in humans. 113 00:06:51,670 --> 00:06:56,490 That they know now from diffusion tensor imaging. 114 00:06:56,490 --> 00:06:57,740 Here's the ventral stream. 115 00:06:57,740 --> 00:07:00,190 And we know there are pathways going 116 00:07:00,190 --> 00:07:04,900 from the inferior temporal lobe into the ventral part 117 00:07:04,900 --> 00:07:06,095 of the prefrontal cortex. 118 00:07:08,910 --> 00:07:13,380 Now, if I look at pathways from those areas, 119 00:07:13,380 --> 00:07:16,040 either from striate and prestriate areas, 120 00:07:16,040 --> 00:07:19,141 or from these areas in the frontal lobe, most of them 121 00:07:19,141 --> 00:07:22,170 in the frontal eye fields, an area 122 00:07:22,170 --> 00:07:27,860 very important for our working memory 123 00:07:27,860 --> 00:07:33,030 of things we're looking at-- we retain, briefly, positions 124 00:07:33,030 --> 00:07:34,130 of things around us. 125 00:07:34,130 --> 00:07:37,090 It affects the way we plan movements. 126 00:07:37,090 --> 00:07:39,040 But look at where they project. 127 00:07:39,040 --> 00:07:42,280 Basically, you find projections from the frontal eye fields 128 00:07:42,280 --> 00:07:45,970 that are matched by projections from prestriate and striate. 129 00:07:45,970 --> 00:07:52,194 For one thing, they go to the superior colliculus. 130 00:07:52,194 --> 00:07:54,360 That would be the major structure there, the largest 131 00:07:54,360 --> 00:07:54,860 structure. 132 00:07:58,400 --> 00:08:02,820 And we know what that's concerned with, 133 00:08:02,820 --> 00:08:05,330 head and eye orienting. 134 00:08:05,330 --> 00:08:08,040 But they also go to the corpus striatum, 135 00:08:08,040 --> 00:08:10,460 either directly from the occipital area 136 00:08:10,460 --> 00:08:12,870 or through the frontal eye fields. 137 00:08:12,870 --> 00:08:14,645 They also go to the subthalamus and 138 00:08:14,645 --> 00:08:18,960 the ventral lateral geniculate body. 139 00:08:18,960 --> 00:08:22,820 If we look at the other areas, the ventral stream 140 00:08:22,820 --> 00:08:25,470 from the inferior temporal cortex, 141 00:08:25,470 --> 00:08:30,850 we get pathways to the amygdala, first described by Nauta. 142 00:08:30,850 --> 00:08:34,780 We get pathways from the amygdala 143 00:08:34,780 --> 00:08:37,280 or directly from the inferior temporal cortex going 144 00:08:37,280 --> 00:08:39,299 into the ventral prefrontal areas. 145 00:08:39,299 --> 00:08:43,289 That ventral prefrontal association cortex 146 00:08:43,289 --> 00:08:47,990 is the only area of neocortex that projects directly 147 00:08:47,990 --> 00:08:50,380 to the hypothalamus. 148 00:08:50,380 --> 00:08:52,730 Now, there's other endbrain structures, 149 00:08:52,730 --> 00:08:54,760 like hippocampus or amygdala, that 150 00:08:54,760 --> 00:08:57,630 project directly to hypothalamus. 151 00:08:57,630 --> 00:08:59,800 But this is the only neocortical area 152 00:08:59,800 --> 00:09:02,250 that has a reasonably strong projection there. 153 00:09:02,250 --> 00:09:04,190 I don't show it being really strong, 154 00:09:04,190 --> 00:09:08,170 because in comparative terms it isn't. 155 00:09:08,170 --> 00:09:10,750 A heavier projection goes to the ventral parts 156 00:09:10,750 --> 00:09:15,140 of the striatum, the ventral striatum. 157 00:09:15,140 --> 00:09:19,650 Very important in habit learning, as we know. 158 00:09:19,650 --> 00:09:21,970 And that has heavy projections to the hypothalamus. 159 00:09:25,350 --> 00:09:29,940 The third pathway is concerned with allocentric orientation. 160 00:09:29,940 --> 00:09:32,840 And this was seen by Nauta in his studies 161 00:09:32,840 --> 00:09:35,560 of prefrontal cortex. 162 00:09:35,560 --> 00:09:38,200 But he included, in his reviews of this, 163 00:09:38,200 --> 00:09:40,995 a number of pathways he had discovered. 164 00:09:40,995 --> 00:09:43,730 And I found in two different papers, 165 00:09:43,730 --> 00:09:47,030 he had traced pathways from that posterior parietal 166 00:09:47,030 --> 00:09:52,370 area, the same area that we know projects to the frontal eye 167 00:09:52,370 --> 00:09:53,400 field. 168 00:09:53,400 --> 00:09:59,020 It has a medial stream but projects, 169 00:09:59,020 --> 00:10:01,510 not just to cingulate cortex there, 170 00:10:01,510 --> 00:10:04,870 but to the retrosplenial area and parahippocampal gyrus. 171 00:10:04,870 --> 00:10:11,290 These are all areas that project to the hippocampus. 172 00:10:11,290 --> 00:10:19,110 That means they're concerned with where the animal is 173 00:10:19,110 --> 00:10:21,910 in spatial-- that kind of memory. 174 00:10:25,480 --> 00:10:28,840 So I consider that to be on a par with the other two 175 00:10:28,840 --> 00:10:29,530 pathways. 176 00:10:29,530 --> 00:10:31,600 So I'm going to call it-- you could call it 177 00:10:31,600 --> 00:10:34,030 the medial stream. 178 00:10:34,030 --> 00:10:36,030 But sometimes it's represented this way, 179 00:10:36,030 --> 00:10:40,370 which is why I guess I didn't use those terms in my book. 180 00:10:40,370 --> 00:10:42,110 It's sometimes shown in the lateral view. 181 00:10:42,110 --> 00:10:45,080 But knowing that anatomy, I think 182 00:10:45,080 --> 00:10:46,910 this is the better way to show it, 183 00:10:46,910 --> 00:10:51,365 because you could show the one going here. 184 00:10:51,365 --> 00:10:53,930 The parahippocampal gyrus, you could easily 185 00:10:53,930 --> 00:10:57,210 show it going around the edge like this. 186 00:10:57,210 --> 00:11:00,580 But this way it shows the whole pathway much better. 187 00:11:04,330 --> 00:11:06,460 I'm not going to spend a lot of time talking. 188 00:11:06,460 --> 00:11:09,300 I just want to mention one thing about transcortical pathways 189 00:11:09,300 --> 00:11:11,750 from a theoretical viewpoint. 190 00:11:11,750 --> 00:11:13,510 Just from a theoretical standpoint, 191 00:11:13,510 --> 00:11:17,260 you could have nearby cortical areas just project 192 00:11:17,260 --> 00:11:19,360 to the nearby areas. 193 00:11:19,360 --> 00:11:24,740 But always, to just say, three other areas. 194 00:11:24,740 --> 00:11:27,930 That would be called absolute connectivity. 195 00:11:27,930 --> 00:11:31,700 They all project to three nearby areas. 196 00:11:31,700 --> 00:11:35,820 Or you could have them all project to all of the others. 197 00:11:35,820 --> 00:11:39,520 That would be proportional connectivity. 198 00:11:39,520 --> 00:11:43,630 That would involve enormous increases in white matter, 199 00:11:43,630 --> 00:11:47,080 as neocortical number increased. 200 00:11:47,080 --> 00:11:54,320 We know, from the way-- if you plot the volume of cortex 201 00:11:54,320 --> 00:11:57,160 versus the volume of the white matter, 202 00:11:57,160 --> 00:12:02,470 that they tend to-- it's fairly linear the way 203 00:12:02,470 --> 00:12:04,440 they're correlated. 204 00:12:04,440 --> 00:12:08,860 So we know it's got to be something closer to this. 205 00:12:08,860 --> 00:12:12,860 But we also know that there are some of these long connections, 206 00:12:12,860 --> 00:12:14,370 like we just talked about. 207 00:12:14,370 --> 00:12:20,564 That type of connectivity is called small world 208 00:12:20,564 --> 00:12:21,105 architecture. 209 00:12:24,790 --> 00:12:30,890 And it's good to actually take a look at that, 210 00:12:30,890 --> 00:12:34,110 because it's so general in its relevance. 211 00:12:34,110 --> 00:12:37,360 Small world network connectivity is 212 00:12:37,360 --> 00:12:41,160 basic to allow social communication. 213 00:12:41,160 --> 00:12:43,310 It's basic to the spread of disease, 214 00:12:43,310 --> 00:12:46,360 and so on and so forth-- not just to the brain. 215 00:12:46,360 --> 00:12:50,110 But what it means is you have regular connectivity. 216 00:12:50,110 --> 00:12:53,180 Each area or each cell-- if you want to, 217 00:12:53,180 --> 00:12:54,550 it can apply whole areas. 218 00:12:54,550 --> 00:12:55,690 It can apply to cells. 219 00:12:55,690 --> 00:13:01,940 They can access a number of nearby areas plus some random-- 220 00:13:01,940 --> 00:13:05,710 then, in theoretical terms, we just say the random. 221 00:13:05,710 --> 00:13:09,590 This would be completely random here, 222 00:13:09,590 --> 00:13:13,890 with no bias towards connecting to local areas, completely 223 00:13:13,890 --> 00:13:14,920 random. 224 00:13:14,920 --> 00:13:17,380 In the middle here, in small world architecture, 225 00:13:17,380 --> 00:13:19,710 you have the connection to nearby areas 226 00:13:19,710 --> 00:13:24,760 plus a few long connections. 227 00:13:24,760 --> 00:13:30,220 And it appears that those long connections that have evolved 228 00:13:30,220 --> 00:13:33,315 did evolve for very specific adaptive reasons. 229 00:13:36,260 --> 00:13:38,700 So we will not say they're random. 230 00:13:38,700 --> 00:13:40,580 But the result is still something 231 00:13:40,580 --> 00:13:42,570 like small world architecture. 232 00:13:42,570 --> 00:13:45,040 And they've plotted the amount of clustering, 233 00:13:45,040 --> 00:13:47,170 the amount of separation, how quickly can you 234 00:13:47,170 --> 00:13:49,030 get from one spot to the other. 235 00:13:49,030 --> 00:13:52,970 It's a very efficient kind of wiring. 236 00:13:52,970 --> 00:13:57,320 And they've studied pathways in the visual system 237 00:13:57,320 --> 00:13:59,930 in those terms and confirmed that it's 238 00:13:59,930 --> 00:14:01,550 a kind of small world architecture. 239 00:14:10,970 --> 00:14:13,880 So now I want to spend a couple of classes 240 00:14:13,880 --> 00:14:17,280 on the auditory system. 241 00:14:17,280 --> 00:14:21,650 And if you have the book, there are a few mistakes 242 00:14:21,650 --> 00:14:25,190 in this chapters, because it was the last chapter-- 243 00:14:25,190 --> 00:14:28,290 I didn't like one of the figures the artist had helped me with. 244 00:14:28,290 --> 00:14:29,540 So I threw it out. 245 00:14:29,540 --> 00:14:31,290 And I put another one in. 246 00:14:31,290 --> 00:14:32,980 And I did change the figure legend. 247 00:14:32,980 --> 00:14:34,302 But I didn't change the text. 248 00:14:34,302 --> 00:14:35,885 And there were a couple of other areas 249 00:14:35,885 --> 00:14:39,450 that-- obviously, it was done last minute. 250 00:14:39,450 --> 00:14:41,530 Not a very good way to finish things up, 251 00:14:41,530 --> 00:14:43,860 but that was the auditory system chapter. 252 00:14:43,860 --> 00:14:46,400 So on page-- I can tell you exactly. 253 00:14:46,400 --> 00:14:47,910 If you want to note this down, you 254 00:14:47,910 --> 00:14:49,701 can just make the corrections in your book, 255 00:14:49,701 --> 00:14:52,320 because I, of course, didn't have all your books. 256 00:14:52,320 --> 00:14:56,390 Page 424 and 425, let me just point those out. 257 00:14:56,390 --> 00:14:58,180 You'll remember them if I just tell you. 258 00:14:58,180 --> 00:14:59,679 You don't have to write it down now. 259 00:14:59,679 --> 00:15:04,660 But if you find that you've got your book-- on page 424, 260 00:15:04,660 --> 00:15:09,300 you'll see a figure were they called the stapes, which 261 00:15:09,300 --> 00:15:12,070 is one of the bones in the middle 262 00:15:12,070 --> 00:15:15,210 here, the one that connects to the eardrum, 263 00:15:15,210 --> 00:15:16,860 the tympanic membrane. 264 00:15:16,860 --> 00:15:19,510 They call it "staples". 265 00:15:19,510 --> 00:15:25,951 The artist didn't-- she had also a spell-checker that changed 266 00:15:25,951 --> 00:15:26,450 it. 267 00:15:26,450 --> 00:15:29,130 And I didn't catch it. 268 00:15:29,130 --> 00:15:33,100 So it should be-- staples is a pretty good term, I guess. 269 00:15:33,100 --> 00:15:36,530 But it's actually the stapes. 270 00:15:36,530 --> 00:15:40,250 And on the other page there's a little parenthetical statement 271 00:15:40,250 --> 00:15:45,330 there, right at the bottom in the text, a parenthesis 272 00:15:45,330 --> 00:15:48,410 where the tectorial membrane is called the tympanic membrane. 273 00:15:48,410 --> 00:15:51,130 I have no idea how I did that. 274 00:15:51,130 --> 00:15:53,640 But I did. 275 00:15:53,640 --> 00:15:56,910 I see that MIT Press now has the glossary 276 00:15:56,910 --> 00:16:01,970 online on the book site. 277 00:16:01,970 --> 00:16:05,430 And there will be an error page, too. 278 00:16:05,430 --> 00:16:08,270 If there are any other errors, please tell me about it, 279 00:16:08,270 --> 00:16:09,800 so we can post those. 280 00:16:09,800 --> 00:16:14,140 And then the next printing, they will get those in. 281 00:16:14,140 --> 00:16:17,560 The second one is in that parenthesis there, 282 00:16:17,560 --> 00:16:20,960 where I say "also the tympanic". 283 00:16:20,960 --> 00:16:22,550 It's not the tympanic. 284 00:16:22,550 --> 00:16:25,806 The tympanic membrane is the eardrum. 285 00:16:25,806 --> 00:16:29,750 It's the tectorial membrane follows 286 00:16:29,750 --> 00:16:34,380 the coils of the cochlea, as does the basilar membrane. 287 00:16:34,380 --> 00:16:35,450 Let's look at that. 288 00:16:35,450 --> 00:16:37,100 We'll look at the pictures. 289 00:16:37,100 --> 00:16:39,500 I just wanted you to correct that in the book. 290 00:16:39,500 --> 00:16:41,410 And I think I actually-- you see, 291 00:16:41,410 --> 00:16:44,610 my original figure was an unrolled cochlea. 292 00:16:44,610 --> 00:16:47,090 And I think I still call it an unrolled cochlea, 293 00:16:47,090 --> 00:16:49,780 because that's what didn't get changed 294 00:16:49,780 --> 00:16:52,040 to correspond to the new figure. 295 00:16:52,040 --> 00:16:52,790 It doesn't matter. 296 00:16:52,790 --> 00:16:54,840 I'll show you the unrolled, so you'll 297 00:16:54,840 --> 00:16:57,880 see what the original figure looked like. 298 00:16:57,880 --> 00:17:00,550 In the first class, I'm going to talk a little bit 299 00:17:00,550 --> 00:17:04,060 about early development and why the audition 300 00:17:04,060 --> 00:17:06,609 evolved the way it did, especially 301 00:17:06,609 --> 00:17:11,160 defensive and anti-predator predator behaviors, but also 302 00:17:11,160 --> 00:17:15,190 special abilities needed especially by predators. 303 00:17:15,190 --> 00:17:17,849 And then a little bit about the cochlear nuclei 304 00:17:17,849 --> 00:17:21,099 and the structures they're connected with. 305 00:17:21,099 --> 00:17:22,810 And then the next class, we'll talk 306 00:17:22,810 --> 00:17:27,710 about the separation of localization and pattern 307 00:17:27,710 --> 00:17:28,369 detection. 308 00:17:28,369 --> 00:17:31,950 It's quite different in audition than vision. 309 00:17:31,950 --> 00:17:34,150 But in the cortex, it ends up having 310 00:17:34,150 --> 00:17:37,250 some very great similarities to what we just talked about. 311 00:17:40,990 --> 00:17:43,730 And then we'll have time to talk a little bit 312 00:17:43,730 --> 00:17:48,020 about specializations in the auditory system, echolocation, 313 00:17:48,020 --> 00:17:49,440 bird song, speech. 314 00:17:53,400 --> 00:18:03,510 So in the embryology of the brain stem, 315 00:18:03,510 --> 00:18:08,800 there are-- you've heard about the mechanosensory lateral line 316 00:18:08,800 --> 00:18:11,020 and the elecrotsensory lateral line. 317 00:18:11,020 --> 00:18:14,690 But we know that that doesn't occur in a lot of species. 318 00:18:14,690 --> 00:18:21,790 But there are auditory placodes in the head area that 319 00:18:21,790 --> 00:18:25,440 lead to the formation of the primary sensory neurons 320 00:18:25,440 --> 00:18:28,780 in both the auditory and vestibular systems. 321 00:18:28,780 --> 00:18:31,300 These are present in all the vertebrate groups. 322 00:18:31,300 --> 00:18:34,707 So they're not like the lateral line systems. 323 00:18:40,320 --> 00:18:44,570 There's just two cranial nerves involved 324 00:18:44,570 --> 00:18:48,580 that, in fact, combine auditory and vestibular. 325 00:18:48,580 --> 00:18:51,500 We group them together in the eighth cranial nerve. 326 00:18:51,500 --> 00:18:53,370 They're actually separate. 327 00:18:53,370 --> 00:18:57,190 But they follow a route into the hindbrain. 328 00:18:57,190 --> 00:18:59,780 They follow the same route. 329 00:18:59,780 --> 00:19:02,840 They're just two branches of the eighth nerve, one 330 00:19:02,840 --> 00:19:05,930 going to the vestibular canals, one going to the cochlea. 331 00:19:09,860 --> 00:19:12,350 I want to just summarize visual pathways. 332 00:19:12,350 --> 00:19:15,390 The first picture, I didn't even put right at the beginning 333 00:19:15,390 --> 00:19:19,190 there in the book, because it looks so complex. 334 00:19:19,190 --> 00:19:20,910 So it's this one. 335 00:19:20,910 --> 00:19:24,540 It's shown on the schematic of a mammalian brain. 336 00:19:24,540 --> 00:19:28,120 You see the cochlea, the cartoon here. 337 00:19:28,120 --> 00:19:31,149 And then I show the enlargement here of the eighth nerve coming 338 00:19:31,149 --> 00:19:32,190 into the cochlear nuclei. 339 00:19:34,930 --> 00:19:39,430 DCN, AVCN, dorsal cochlear nucleus, 340 00:19:39,430 --> 00:19:41,850 and anteroventral cochlear nucleus. 341 00:19:41,850 --> 00:19:44,600 You can just think of it as the ventral cochlear nucleus. 342 00:19:44,600 --> 00:19:48,240 There is an anterior and a posterior part. 343 00:19:48,240 --> 00:19:53,660 And then we can follow various routes. 344 00:19:53,660 --> 00:19:56,780 Now what were those-- let's first of all 345 00:19:56,780 --> 00:19:58,520 just simplify this whole thing. 346 00:19:58,520 --> 00:20:05,780 But you see there's a reflex pathway here going locally, 347 00:20:05,780 --> 00:20:07,590 getting to a motor neuron. 348 00:20:07,590 --> 00:20:10,280 There's pathways like that controlling the startle reflex, 349 00:20:10,280 --> 00:20:12,340 for example. 350 00:20:12,340 --> 00:20:14,690 And then you see a pathway to the cerebellum. 351 00:20:14,690 --> 00:20:16,450 So there's cerebellar pathways. 352 00:20:16,450 --> 00:20:18,800 That's one of the lemniscal pathways. 353 00:20:18,800 --> 00:20:21,580 And then other lemniscal pathways, 354 00:20:21,580 --> 00:20:23,620 which in the auditory system, at first wash, 355 00:20:23,620 --> 00:20:25,170 seem really complicated. 356 00:20:25,170 --> 00:20:26,890 Some of them are straightforward, 357 00:20:26,890 --> 00:20:30,090 going to inferior colliculus, then to the medial geniculate 358 00:20:30,090 --> 00:20:33,030 body, then to the auditory cortex. 359 00:20:33,030 --> 00:20:36,740 Others seem complicated. 360 00:20:36,740 --> 00:20:39,130 One goes to the ventral part of the hindbrain. 361 00:20:39,130 --> 00:20:43,420 And then that projects by means of other nuclei 362 00:20:43,420 --> 00:20:46,980 into the inferior colliculus. 363 00:20:46,980 --> 00:20:49,650 And from that region, you also have 364 00:20:49,650 --> 00:20:53,734 pathways that totally bypass the inferior colliculus. 365 00:20:53,734 --> 00:20:56,150 In fact, they don't even go to the medial geniculate body. 366 00:20:56,150 --> 00:20:58,380 They go to structures around it. 367 00:20:58,380 --> 00:20:59,860 So it seems complicated. 368 00:20:59,860 --> 00:21:04,580 So I've just drawn this kind of simplified diagram 369 00:21:04,580 --> 00:21:06,090 of the ascending pathways. 370 00:21:09,357 --> 00:21:10,940 So the peripheral ganglia, these would 371 00:21:10,940 --> 00:21:13,100 be the primary sensory neurons. 372 00:21:13,100 --> 00:21:16,370 Then you get to the secondary sensory nuclei, the cochlear 373 00:21:16,370 --> 00:21:18,590 nuclei. 374 00:21:18,590 --> 00:21:22,516 But also in hindbrain, you have tertiary structures 375 00:21:22,516 --> 00:21:24,850 in the ventral part of the hindbrain. 376 00:21:29,170 --> 00:21:34,210 And then, both of these kinds of structures in the hindbrain 377 00:21:34,210 --> 00:21:37,215 project to the midbrain, with just a few axons 378 00:21:37,215 --> 00:21:40,660 in the mammals-- at least in some mammals, 379 00:21:40,660 --> 00:21:42,680 they may not happen in all. 380 00:21:42,680 --> 00:21:44,799 They go directly to the medial geniculate body. 381 00:21:44,799 --> 00:21:46,590 And that would be the only thing like, say, 382 00:21:46,590 --> 00:21:49,900 the retinal geniculate pathway. 383 00:21:49,900 --> 00:21:53,290 It goes directly to the thalamus and the retina. 384 00:21:53,290 --> 00:21:57,024 Here we have the dorsal cochlear nucleus and some axons 385 00:21:57,024 --> 00:21:58,440 directly to the medial geniculate. 386 00:21:58,440 --> 00:22:00,700 Most of them go into the midbrain. 387 00:22:00,700 --> 00:22:03,420 And I give the name there, inferior colliculus, 388 00:22:03,420 --> 00:22:05,350 for the mammals. 389 00:22:05,350 --> 00:22:07,370 But it's got other names in non-mammals, 390 00:22:07,370 --> 00:22:09,890 the torus semicircularis. 391 00:22:09,890 --> 00:22:12,210 If you were looking at a bird or reptile, 392 00:22:12,210 --> 00:22:14,280 it would be called that. 393 00:22:14,280 --> 00:22:18,400 Then you have the diencephalon or tween brain, not just 394 00:22:18,400 --> 00:22:19,930 the medial geniculate, though that's 395 00:22:19,930 --> 00:22:23,930 the main one, but the posterior nuclear group, or group 396 00:22:23,930 --> 00:22:26,583 of nuclei that are around that structure. 397 00:22:30,140 --> 00:22:32,950 And you also have the old thalamus, the intralaminar 398 00:22:32,950 --> 00:22:33,580 nuclei. 399 00:22:33,580 --> 00:22:36,860 They also get input from the midbrain, 400 00:22:36,860 --> 00:22:38,260 carrying auditory information. 401 00:22:38,260 --> 00:22:42,832 Though it tends to overlap with the visual and somatosensory. 402 00:22:42,832 --> 00:22:44,800 And then finally, the endbrain. 403 00:22:44,800 --> 00:22:47,850 And I point out, not only auditory cortex, 404 00:22:47,850 --> 00:22:52,210 but also part of the amygdala get direct connections 405 00:22:52,210 --> 00:22:54,100 from the auditory thalamus. 406 00:23:00,200 --> 00:23:02,410 And then of course, the intralaminar nuclei 407 00:23:02,410 --> 00:23:06,230 that also go to the striatum, not only to the cortex. 408 00:23:06,230 --> 00:23:12,550 So let's talk a little bit about the evolution of this system 409 00:23:12,550 --> 00:23:15,810 before we go back to some of these details 410 00:23:15,810 --> 00:23:18,070 and try to pick out the main things. 411 00:23:21,580 --> 00:23:27,280 We know that escape behavior is always given precedence 412 00:23:27,280 --> 00:23:30,140 in evolution, because it's so critical 413 00:23:30,140 --> 00:23:31,773 that the animal survive. 414 00:23:31,773 --> 00:23:35,220 Or he can't reproduce. 415 00:23:35,220 --> 00:23:37,930 So I'm asking you a behavioral question, here. 416 00:23:37,930 --> 00:23:42,330 If you've had my 920 class, you might remember this. 417 00:23:42,330 --> 00:23:46,890 I said describe an example of a fixed action pattern that 418 00:23:46,890 --> 00:23:50,940 is instinctive, pre-wired behavior, that's 419 00:23:50,940 --> 00:23:56,750 triggered in small mammals by the sounds of a predator. 420 00:23:56,750 --> 00:24:00,730 In fact, it's usually triggered by any really novel stimuli. 421 00:24:00,730 --> 00:24:02,110 AUDIENCE: Freezing. 422 00:24:02,110 --> 00:24:03,920 PROFESSOR: Freezing, very simple. 423 00:24:03,920 --> 00:24:07,060 Freezing is a very common first response. 424 00:24:07,060 --> 00:24:09,090 What good is that? 425 00:24:09,090 --> 00:24:13,130 Most predators detect motion. 426 00:24:13,130 --> 00:24:16,750 And so if the animal freezes, it pretty much 427 00:24:16,750 --> 00:24:20,300 disappears from the attention of the predator. 428 00:24:20,300 --> 00:24:22,760 So very important. 429 00:24:22,760 --> 00:24:25,130 If you're a hamster, for example, 430 00:24:25,130 --> 00:24:26,880 the first thing they will do is freeze 431 00:24:26,880 --> 00:24:29,240 if there's a novel stimulus. 432 00:24:29,240 --> 00:24:34,250 If the stimulus increases in spite of their freezing, 433 00:24:34,250 --> 00:24:38,480 then you will get-- just like that visual response 434 00:24:38,480 --> 00:24:40,960 we talked about-- you'll get rapid running. 435 00:24:40,960 --> 00:24:45,890 They don't run in any particular direction with respect 436 00:24:45,890 --> 00:24:46,840 to the predator. 437 00:24:46,840 --> 00:24:50,200 They run towards a safe haven. 438 00:24:50,200 --> 00:24:51,280 They run to their tunnel. 439 00:24:51,280 --> 00:24:53,339 They run to a hiding place. 440 00:24:53,339 --> 00:24:54,880 So that's when they use their tectum. 441 00:24:57,460 --> 00:25:01,370 But what is triggered is then secondary to the rapid running. 442 00:25:01,370 --> 00:25:04,130 And there's some other beautiful fixed action patterns. 443 00:25:04,130 --> 00:25:07,500 I probably described in the book the kangaroo rat 444 00:25:07,500 --> 00:25:10,316 that responds to a rattlesnake. 445 00:25:10,316 --> 00:25:14,640 He hears the noise of a rattlesnake, the rattle. 446 00:25:14,640 --> 00:25:19,180 And the kangaroo rat does freeze. 447 00:25:19,180 --> 00:25:22,060 And then he does something really odd. 448 00:25:22,060 --> 00:25:25,700 He just waits for the attack. 449 00:25:25,700 --> 00:25:27,250 The rattlesnake attacks. 450 00:25:27,250 --> 00:25:29,000 You can imaginee-- here's that open mouth, 451 00:25:29,000 --> 00:25:32,890 rushing towards the kangaroo rat. 452 00:25:32,890 --> 00:25:37,110 As the head rushes through the air, the animal's 453 00:25:37,110 --> 00:25:40,950 auditory system-- the kangaroo rat's auditory system 454 00:25:40,950 --> 00:25:45,410 is tuned to respond to the noise of the onrushing rattlesnake 455 00:25:45,410 --> 00:25:46,360 head. 456 00:25:46,360 --> 00:25:51,850 And that triggers a rapid leap, in which he 457 00:25:51,850 --> 00:25:55,560 does a backward somersault, avoids 458 00:25:55,560 --> 00:25:57,220 the head of the rattlesnake. 459 00:25:57,220 --> 00:26:02,650 He lands just outside the range of the rattlesnake and escapes. 460 00:26:02,650 --> 00:26:04,595 It almost always works. 461 00:26:04,595 --> 00:26:05,094 Yes? 462 00:26:05,094 --> 00:26:07,360 AUDIENCE: [INAUDIBLE]. 463 00:26:07,360 --> 00:26:08,270 PROFESSOR: Sorry? 464 00:26:08,270 --> 00:26:10,620 AUDIENCE: [INAUDIBLE]. 465 00:26:10,620 --> 00:26:11,620 PROFESSOR: I don't know. 466 00:26:11,620 --> 00:26:15,930 It's been observed in nature many times. 467 00:26:15,930 --> 00:26:19,410 And they have done special studies of the auditory system. 468 00:26:19,410 --> 00:26:24,536 These animals have huge air spaces around the cochlea. 469 00:26:33,290 --> 00:26:36,830 I think I mentioned the escape behavior of the moth. 470 00:26:36,830 --> 00:26:42,000 Moths that hear the cry of a bat, they dive. 471 00:26:42,000 --> 00:26:44,330 They dive for the ground. 472 00:26:44,330 --> 00:26:46,200 And that's how they escape the bat. 473 00:26:46,200 --> 00:26:49,950 They just fold their wings and go into a nose dive. 474 00:26:49,950 --> 00:26:52,840 It's similarly a rapid escape behavior. 475 00:27:01,560 --> 00:27:05,950 And then I ask a couple questions about two things 476 00:27:05,950 --> 00:27:08,760 closely related to this escape from a predator. 477 00:27:08,760 --> 00:27:13,570 One is the aversion to loud noises the rodents have. 478 00:27:13,570 --> 00:27:16,480 It's been studied best in rats. 479 00:27:16,480 --> 00:27:20,370 It and the other that's also been studied, mostly in rats. 480 00:27:20,370 --> 00:27:23,710 But now it's been studied in other animals as well. 481 00:27:23,710 --> 00:27:26,960 And that is learned fear. 482 00:27:26,960 --> 00:27:30,060 That is, an animal can learn to be 483 00:27:30,060 --> 00:27:35,180 afraid of certain kinds of sounds by training. 484 00:27:35,180 --> 00:27:37,740 You give him a sound, and then you shock his feet. 485 00:27:37,740 --> 00:27:41,230 He becomes afraid and shows a fear response to that sound. 486 00:27:41,230 --> 00:27:44,130 Whereas before, it was just a neutral sound. 487 00:27:44,130 --> 00:27:45,380 That's fear learning. 488 00:27:45,380 --> 00:27:48,130 It's been studied many times. 489 00:27:48,130 --> 00:27:51,150 And it involves pathways, now, that 490 00:27:51,150 --> 00:27:52,580 have been studied very well. 491 00:27:58,370 --> 00:28:05,760 So first of all, in the study of avoidance of very loud noises, 492 00:28:05,760 --> 00:28:07,700 they've done these interesting studies 493 00:28:07,700 --> 00:28:15,050 where they make huge central nervous system lesions. 494 00:28:15,050 --> 00:28:17,610 They'll taking the inferior colliculus out. 495 00:28:17,610 --> 00:28:21,910 They take the entire auditory cortex out. 496 00:28:21,910 --> 00:28:26,130 It doesn't change the way the animal responds to loud noises. 497 00:28:26,130 --> 00:28:29,190 In fact, it doesn't even change his ability 498 00:28:29,190 --> 00:28:34,810 to discriminate different amplitudes of noise 499 00:28:34,810 --> 00:28:36,005 at all-- of sounds. 500 00:28:38,730 --> 00:28:43,090 Because you can study-- teach him 501 00:28:43,090 --> 00:28:47,490 to press a lever to turn of the aversive noise. 502 00:28:47,490 --> 00:28:50,150 And he will keep doing that. 503 00:28:50,150 --> 00:28:54,130 Unless, in the midbrain, you make-- 504 00:28:54,130 --> 00:28:56,970 there's a picture of the left side 505 00:28:56,970 --> 00:29:00,180 of the dorsal midbrain of a hamster. 506 00:29:00,180 --> 00:29:01,565 The studies were done in rats. 507 00:29:01,565 --> 00:29:07,780 But I'm showing here the superficial layers. 508 00:29:07,780 --> 00:29:11,630 The colliculus goes down to about here. 509 00:29:11,630 --> 00:29:13,820 This is called the central gray area. 510 00:29:13,820 --> 00:29:17,600 And there's the aqueduct of Sylvius. 511 00:29:17,600 --> 00:29:21,230 You can see how the central gray stands out. 512 00:29:21,230 --> 00:29:25,060 The ocular motor nuclei would be right here. 513 00:29:25,060 --> 00:29:29,400 They look like just part of the central gray there. 514 00:29:29,400 --> 00:29:31,940 And when they make these large lesions, 515 00:29:31,940 --> 00:29:36,130 they can carve out areas like this. 516 00:29:36,130 --> 00:29:39,170 [INAUDIBLE] on both sides. 517 00:29:39,170 --> 00:29:45,160 And the animal still will press the lever 518 00:29:45,160 --> 00:29:47,160 to turn the loud noise off. 519 00:29:47,160 --> 00:29:49,720 But if you get into this ventral area-- 520 00:29:49,720 --> 00:29:53,890 the lesion goes down here to get all of that area, 521 00:29:53,890 --> 00:29:59,320 just a lesion right there-- will abolish that avoidance 522 00:29:59,320 --> 00:30:03,620 of-- learning to get rid of the loud noise. 523 00:30:03,620 --> 00:30:05,720 So this ventral part of central gray-- and we 524 00:30:05,720 --> 00:30:07,710 know from other studies of central gray 525 00:30:07,710 --> 00:30:12,650 that it's an activation that structure causes. 526 00:30:12,650 --> 00:30:16,410 It's always activated in pain, somatosensory pain. 527 00:30:16,410 --> 00:30:21,080 So apparently, auditory stimuli that they hate, they avoid, 528 00:30:21,080 --> 00:30:26,060 activate these pain mechanisms as well. 529 00:30:26,060 --> 00:30:29,860 So that's what I'm explaining here. 530 00:30:29,860 --> 00:30:34,020 And this just to show you that that central gray part 531 00:30:34,020 --> 00:30:37,820 of the limbic regions, the limbic midbrain regions, 532 00:30:37,820 --> 00:30:40,410 meaning that they get heavy projections 533 00:30:40,410 --> 00:30:44,710 from the hypothalamus and from limbic endbrain areas-- 534 00:30:44,710 --> 00:30:47,990 central gray and ventral tegmental area. 535 00:30:47,990 --> 00:30:51,800 But this dorsal part-- if you stimulate that, 536 00:30:51,800 --> 00:30:53,420 animals are uncomfortable. 537 00:30:53,420 --> 00:30:55,760 They will work to turn an electrical stimulus 538 00:30:55,760 --> 00:30:57,620 to that area off. 539 00:30:57,620 --> 00:31:00,270 Whereas if you're down in the ventral tegmental area, 540 00:31:00,270 --> 00:31:02,470 it's the opposite. 541 00:31:02,470 --> 00:31:06,020 They seem to be rewarded by stimulating there. 542 00:31:06,020 --> 00:31:08,520 It's a pleasurable result. 543 00:31:16,330 --> 00:31:18,890 Now, you can also-- as I mentioned, 544 00:31:18,890 --> 00:31:22,140 you can expose the animal to sounds, 545 00:31:22,140 --> 00:31:25,800 say a tone of a certain frequency, 546 00:31:25,800 --> 00:31:28,260 and shock the feet of the animal. 547 00:31:28,260 --> 00:31:30,230 And he becomes afraid of the sound. 548 00:31:30,230 --> 00:31:34,830 Now, that learning is not specific 549 00:31:34,830 --> 00:31:37,020 to the central gray regions. 550 00:31:37,020 --> 00:31:40,270 That kind of learning-- as is often true, learning 551 00:31:40,270 --> 00:31:43,550 tends to depend on the forebrain. 552 00:31:43,550 --> 00:31:46,860 In this case, we know the pathway goes to the amygdala. 553 00:31:46,860 --> 00:31:51,410 And this is a study of that pathway. 554 00:31:51,410 --> 00:31:52,865 Here in the opossum, the hedgehog, 555 00:31:52,865 --> 00:31:59,120 and [? the treeshoe. ?] It looks like my labels 556 00:31:59,120 --> 00:32:01,200 moved a little bit wrongly there. 557 00:32:01,200 --> 00:32:02,600 But what they're doing is they're 558 00:32:02,600 --> 00:32:10,700 putting a label or a lesion in much of the medial geniculate 559 00:32:10,700 --> 00:32:15,610 body, the thalamic structure that's 560 00:32:15,610 --> 00:32:17,000 sending auditory pathways. 561 00:32:17,000 --> 00:32:19,050 They've done it in all three animals. 562 00:32:19,050 --> 00:32:21,230 And then they trace all the axons, 563 00:32:21,230 --> 00:32:25,150 from medial geniculate body forward into the endbrain. 564 00:32:25,150 --> 00:32:28,720 So here you see them coming out of the internal capsule 565 00:32:28,720 --> 00:32:34,140 and going very heavily to the amygdala in the opossum. 566 00:32:34,140 --> 00:32:37,730 They also go, of course, to the auditory neocortex. 567 00:32:40,380 --> 00:32:42,910 You see the same thing here in the hedgehog. 568 00:32:42,910 --> 00:32:46,770 The same thing here in the [? treeshoe. ?] But notice, 569 00:32:46,770 --> 00:32:50,090 in the [? treeshoe ?], in relative terms, 570 00:32:50,090 --> 00:32:52,560 it has a bigger neocortex. 571 00:32:52,560 --> 00:32:56,840 The auditory projections, the neocortex is the larger one. 572 00:32:56,840 --> 00:32:58,710 In the opossum, the two projections 573 00:32:58,710 --> 00:33:00,680 are both very large. 574 00:33:00,680 --> 00:33:02,690 In the hedgehog, they're both large. 575 00:33:02,690 --> 00:33:04,390 But again, the one from the neocortex 576 00:33:04,390 --> 00:33:05,860 is a little bit larger. 577 00:33:05,860 --> 00:33:08,970 The hamster would be similar to the hedgehog, here. 578 00:33:08,970 --> 00:33:09,970 So would the mouse. 579 00:33:13,450 --> 00:33:15,330 So that's something we didn't talk about 580 00:33:15,330 --> 00:33:16,800 in the visual system. 581 00:33:16,800 --> 00:33:18,430 It's not been as well studied. 582 00:33:18,430 --> 00:33:26,460 But now, we know there are visual pathways also going 583 00:33:26,460 --> 00:33:29,960 through the thalamus, but not the lateral geniculate body, 584 00:33:29,960 --> 00:33:32,620 through parts of the lateral nucleus that 585 00:33:32,620 --> 00:33:36,410 reach the amygdala without going to the visual cortex. 586 00:33:39,180 --> 00:33:42,110 But it's the pathway in the auditory system that's 587 00:33:42,110 --> 00:33:45,310 been the most studies, which is why we talk about it here. 588 00:33:49,940 --> 00:33:54,710 Now especially predators-- they don't have to do-- they still, 589 00:33:54,710 --> 00:33:56,280 when they're young especially, they 590 00:33:56,280 --> 00:33:59,500 have to have those escape responses, too. 591 00:33:59,500 --> 00:34:03,310 But when they're older, they're preying on animals. 592 00:34:03,310 --> 00:34:04,890 They need to localize their prey. 593 00:34:04,890 --> 00:34:07,310 They need to identify the prey. 594 00:34:07,310 --> 00:34:13,639 And those kinds of abilities evolved, of course, 595 00:34:13,639 --> 00:34:15,130 in the auditory system, too. 596 00:34:19,110 --> 00:34:22,739 So we need to talk about those pathways, Identifying 597 00:34:22,739 --> 00:34:23,420 and localizing. 598 00:34:26,760 --> 00:34:29,739 So first of all, you need to discriminate differences 599 00:34:29,739 --> 00:34:31,455 in sound frequency. 600 00:34:31,455 --> 00:34:36,219 You need to combine those sound frequencies, temporal patterns 601 00:34:36,219 --> 00:34:38,386 of frequencies in different ways. 602 00:34:38,386 --> 00:34:41,330 You've got to have neurons that can respond specifically 603 00:34:41,330 --> 00:34:43,199 to those things. 604 00:34:43,199 --> 00:34:47,310 And there was an evolution-- very different-- 605 00:34:47,310 --> 00:34:51,320 using auditory cues to localize. 606 00:34:51,320 --> 00:34:55,144 You know that a raptor, like an owl, 607 00:34:55,144 --> 00:34:58,940 is very good at localizing prey by auditory cues. 608 00:34:58,940 --> 00:35:00,040 They have to. 609 00:35:00,040 --> 00:35:02,410 They're night hunters. 610 00:35:02,410 --> 00:35:07,080 So their mean way to detect prey on the forest floor below them 611 00:35:07,080 --> 00:35:09,630 is by auditory cues. 612 00:35:09,630 --> 00:35:13,190 So they can tell that there's a little rustling 613 00:35:13,190 --> 00:35:17,206 in the undergrowth or in the leaves on the forest floor. 614 00:35:17,206 --> 00:35:21,000 They not only hear it, but they know, better than we can, 615 00:35:21,000 --> 00:35:21,500 actually. 616 00:35:21,500 --> 00:35:25,660 They know where that little animal is. 617 00:35:25,660 --> 00:35:27,500 So there was an evolution of apparatus, 618 00:35:27,500 --> 00:35:29,920 producing those cues. 619 00:35:29,920 --> 00:35:31,570 Now, to understand those things, I 620 00:35:31,570 --> 00:35:36,370 want to say a little bit about the initial stages 621 00:35:36,370 --> 00:35:41,342 of the auditory system, the peripheral auditory structures, 622 00:35:41,342 --> 00:35:44,870 or the primary sensory neurons, that's transduction. 623 00:35:44,870 --> 00:35:49,830 And then the initial coding of the auditory stimuli, and then 624 00:35:49,830 --> 00:35:53,590 the channels of conduction involved 625 00:35:53,590 --> 00:35:58,190 in those various functions in the brain. 626 00:35:58,190 --> 00:36:04,570 So first of all, what do you remember about this? 627 00:36:04,570 --> 00:36:10,160 There's a transformation-- a transformation 628 00:36:10,160 --> 00:36:12,930 in the middle ear apparatus occurred 629 00:36:12,930 --> 00:36:14,970 in the early evolution of mammals 630 00:36:14,970 --> 00:36:18,960 that was different from reptiles. 631 00:36:18,960 --> 00:36:23,330 Remember, they evolved the mammal-like reptiles. 632 00:36:23,330 --> 00:36:27,100 And at some point in those mammal-like reptiles, 633 00:36:27,100 --> 00:36:30,600 certainly by the time you get to real mammals, 634 00:36:30,600 --> 00:36:34,220 you had this difference in the middle ear. 635 00:36:34,220 --> 00:36:37,860 If you look in modern reptiles, you don't find it. 636 00:36:37,860 --> 00:36:41,410 But you find it in all mammals. 637 00:36:41,410 --> 00:36:47,230 And it was-- this is the picture that I put in the book. 638 00:36:47,230 --> 00:36:51,760 It shows-- Allman discusses it. 639 00:36:51,760 --> 00:36:55,957 And I think I listed some papers with people 640 00:36:55,957 --> 00:36:57,790 that have studied this and the paleontology. 641 00:37:01,400 --> 00:37:02,540 This is an early mammal. 642 00:37:02,540 --> 00:37:03,630 And this is a dimetradon. 643 00:37:03,630 --> 00:37:05,225 It's one of the mammal-like reptiles. 644 00:37:08,070 --> 00:37:11,250 And in a dimetradon, you see there's 645 00:37:11,250 --> 00:37:14,025 the stapes bone of the middle ear. 646 00:37:14,025 --> 00:37:17,910 But it goes directly from the eardrum 647 00:37:17,910 --> 00:37:25,830 into the oval window at the entrance to the cochlea. 648 00:37:25,830 --> 00:37:28,870 In mammals, you have three bones. 649 00:37:28,870 --> 00:37:32,117 Two of those bones were jawbones in reptiles. 650 00:37:35,100 --> 00:37:37,070 They evolved into middle ear bones. 651 00:37:40,694 --> 00:37:41,860 We don't know all the steps. 652 00:37:41,860 --> 00:37:48,740 But we have enough skills to know about when that occurred. 653 00:37:48,740 --> 00:37:51,930 So what's going on in the middle ear? 654 00:37:51,930 --> 00:37:55,210 What do you have to do in the middle ear? 655 00:37:55,210 --> 00:37:59,740 Sound is a vibration, movement in air. 656 00:37:59,740 --> 00:38:03,670 And it causes vibrations of the eardrum, tympanic membrane. 657 00:38:07,010 --> 00:38:12,740 We've got to get to vibrations of the fluid in the cochlea. 658 00:38:12,740 --> 00:38:15,950 That requires some impedance matching. 659 00:38:15,950 --> 00:38:19,330 And that can be inefficient or efficient. 660 00:38:19,330 --> 00:38:22,130 It happens, of course, through the stapes here 661 00:38:22,130 --> 00:38:27,510 in the reptiles, directly from eardrum to the inner ear. 662 00:38:27,510 --> 00:38:31,460 But now you've got the vibrations in response 663 00:38:31,460 --> 00:38:34,450 to the air being transmitted directly 664 00:38:34,450 --> 00:38:36,610 to the fluid of the inner ear. 665 00:38:36,610 --> 00:38:40,090 It turns out there's a more efficient way to do it. 666 00:38:40,090 --> 00:38:41,840 These little bones are connected. 667 00:38:41,840 --> 00:38:43,500 So there's a hinging. 668 00:38:43,500 --> 00:38:44,790 It changes. 669 00:38:44,790 --> 00:38:49,090 There's a greater movement of the outer bone 670 00:38:49,090 --> 00:38:50,378 that of the stapes. 671 00:38:50,378 --> 00:38:51,464 Yes? 672 00:38:51,464 --> 00:38:52,380 AUDIENCE: [INAUDIBLE]. 673 00:39:00,200 --> 00:39:02,220 PROFESSOR: They usually don't have any. 674 00:39:02,220 --> 00:39:04,160 They do have some external ear. 675 00:39:04,160 --> 00:39:07,840 But some of them don't even at all. 676 00:39:07,840 --> 00:39:11,925 But they do have-- I mean, this is a reptile. 677 00:39:14,690 --> 00:39:17,010 Of course, actually, from the paleontology, 678 00:39:17,010 --> 00:39:18,814 we don't know every detail. 679 00:39:18,814 --> 00:39:20,105 But we know from the dentition. 680 00:39:20,105 --> 00:39:23,840 And we know from the ear bones and a number of other features 681 00:39:23,840 --> 00:39:26,760 that are different in reptiles and mammals. 682 00:39:26,760 --> 00:39:29,240 And that's how they identify it. 683 00:39:29,240 --> 00:39:31,740 We also know because the eye region is different. 684 00:39:31,740 --> 00:39:34,050 There was actually some reduction 685 00:39:34,050 --> 00:39:36,560 in the bones around the eye in the earliest mammals. 686 00:39:39,480 --> 00:39:43,010 All right, so it was an impedance matching problem. 687 00:39:43,010 --> 00:39:45,850 And the result of getting better impedance matching 688 00:39:45,850 --> 00:39:50,570 was response to higher frequencies. 689 00:39:50,570 --> 00:39:54,440 So here's a turtle. 690 00:39:54,440 --> 00:39:58,950 And look at the-- he responds-- he doesn't respond well 691 00:39:58,950 --> 00:40:01,905 to tones above about 10 kilohertz. 692 00:40:05,330 --> 00:40:07,040 Here's a bird. 693 00:40:07,040 --> 00:40:08,000 This is a median. 694 00:40:08,000 --> 00:40:13,290 But the bird's range-- or in this range, 695 00:40:13,290 --> 00:40:14,360 they respond higher. 696 00:40:14,360 --> 00:40:16,150 But look at some of these mammals. 697 00:40:16,150 --> 00:40:19,400 They can respond to very high sounds. 698 00:40:19,400 --> 00:40:24,410 Many mammals here, well above the human range of hearing. 699 00:40:24,410 --> 00:40:28,880 And young humans can hear up pretty high, too. 700 00:40:28,880 --> 00:40:31,020 You can probably hear considerably higher 701 00:40:31,020 --> 00:40:35,620 than I can, because a lot of that's lost with age. 702 00:40:35,620 --> 00:40:42,700 So that was a big change, because now young, 703 00:40:42,700 --> 00:40:46,910 when they're having difficulties, emit cries. 704 00:40:46,910 --> 00:40:52,510 And for mammals, those cries are mostly very high frequency. 705 00:40:52,510 --> 00:40:55,620 When we have these pups born in the lab, 706 00:40:55,620 --> 00:40:57,940 we hear a little bit of squeaking from the young. 707 00:40:57,940 --> 00:41:00,010 But in fact, a lot of it, we don't even hear, 708 00:41:00,010 --> 00:41:02,250 because it's way above our hearing range. 709 00:41:02,250 --> 00:41:04,160 But the mothers can hear it. 710 00:41:04,160 --> 00:41:07,730 The reptiles don't hear it. 711 00:41:07,730 --> 00:41:12,140 That gave a big advantage to the earliest mammals. 712 00:41:12,140 --> 00:41:14,190 They evolved at a time when reptiles 713 00:41:14,190 --> 00:41:16,225 were the dominant tetrapod. 714 00:41:20,000 --> 00:41:23,055 So here you see where that ear apparatus is located. 715 00:41:25,960 --> 00:41:30,900 This is the middle ear chamber, an air-filled chamber connected 716 00:41:30,900 --> 00:41:34,776 to throat, by means of the Eustachian tube here. 717 00:41:34,776 --> 00:41:37,370 So there's the eardrum. 718 00:41:37,370 --> 00:41:45,770 There's the round window-- or the-- I always mix them up. 719 00:41:45,770 --> 00:41:47,510 It's the oval window. 720 00:41:47,510 --> 00:41:52,070 So this is the end of the cochlea. 721 00:41:52,070 --> 00:41:54,160 And note that it looks like a snail. 722 00:41:54,160 --> 00:41:59,520 That's because the cochlea is actually an elongated tube. 723 00:41:59,520 --> 00:42:05,090 And so it will fit in the skull, it's coiled up. 724 00:42:05,090 --> 00:42:08,200 So it's actually like this. 725 00:42:08,200 --> 00:42:13,930 This is an unrolled cochlea. 726 00:42:13,930 --> 00:42:16,830 So the apparatus that's sensitive to vibration 727 00:42:16,830 --> 00:42:21,350 of a fluid there runs down the middle. 728 00:42:21,350 --> 00:42:23,780 There's the oval window with the stapes connected 729 00:42:23,780 --> 00:42:26,660 to it, round window at the other side, 730 00:42:26,660 --> 00:42:29,900 So this the vibrations-- the larger vibrations here 731 00:42:29,900 --> 00:42:33,760 are transformed into smaller vibrations here. 732 00:42:33,760 --> 00:42:35,590 That affects that fluid of the cochlea. 733 00:42:35,590 --> 00:42:38,190 And just note that the vestibular 734 00:42:38,190 --> 00:42:42,040 canals-- I didn't like this picture. 735 00:42:42,040 --> 00:42:44,800 It needed to be improved a little bit. 736 00:42:44,800 --> 00:42:49,530 Here you see a picture of the vestibular canals arranged 737 00:42:49,530 --> 00:42:55,960 in three planes that are off to the side 738 00:42:55,960 --> 00:42:58,100 there where the cochlea begins. 739 00:43:01,545 --> 00:43:03,932 AUDIENCE: [INAUDIBLE]. 740 00:43:03,932 --> 00:43:04,640 PROFESSOR: Sorry? 741 00:43:04,640 --> 00:43:05,556 AUDIENCE: [INAUDIBLE]. 742 00:43:12,235 --> 00:43:13,860 PROFESSOR: Yeah, we're going to-- let's 743 00:43:13,860 --> 00:43:16,890 just look at that right now. 744 00:43:16,890 --> 00:43:20,450 This is the-- we call it the organ of Corti. 745 00:43:20,450 --> 00:43:22,930 And if you make a cross section through the cochlea, 746 00:43:22,930 --> 00:43:26,530 you see you're cutting that coil at various points. 747 00:43:26,530 --> 00:43:29,200 This is from [INAUDIBLE], who did a lot of these studies 748 00:43:29,200 --> 00:43:31,940 at Harvard. 749 00:43:31,940 --> 00:43:35,350 This is called the tympanic membrane. 750 00:43:35,350 --> 00:43:39,260 The smaller area here is the tectorial membrane. 751 00:43:39,260 --> 00:43:42,950 And little hair cells run between those two membranes. 752 00:43:42,950 --> 00:43:46,270 So here, you see the organ of Corti enlarged. 753 00:43:46,270 --> 00:43:48,760 So there's the basilar membrane. 754 00:43:48,760 --> 00:43:50,900 There's the tectorial membrane. 755 00:43:50,900 --> 00:43:56,270 And these are the two groups of hair cells. 756 00:43:58,840 --> 00:44:00,840 There's inner hair cells that receive 757 00:44:00,840 --> 00:44:03,125 most of the innervation that's responding to sound. 758 00:44:03,125 --> 00:44:06,340 And the outer hair cells have other functions 759 00:44:06,340 --> 00:44:08,820 that have evolved in mammals, to respond 760 00:44:08,820 --> 00:44:13,030 to those vibrations of the fluid. 761 00:44:13,030 --> 00:44:19,610 It happens because of-- when you get movement of the basilar 762 00:44:19,610 --> 00:44:22,110 membrane, there's movement with respect 763 00:44:22,110 --> 00:44:23,580 to the tectorial membrane. 764 00:44:23,580 --> 00:44:26,360 And it causes a shearing force in those cells. 765 00:44:26,360 --> 00:44:29,250 The little hairs that protrude here 766 00:44:29,250 --> 00:44:34,670 connect this into the cell, to the tectorial membrane. 767 00:44:34,670 --> 00:44:40,950 And it's those shearing forces that these little transduction 768 00:44:40,950 --> 00:44:41,980 cells are responding to. 769 00:44:41,980 --> 00:44:44,660 They are primary sensory neurons. 770 00:44:44,660 --> 00:44:47,530 I'm sorry, they are not-- they are receptor cells. 771 00:44:47,530 --> 00:44:51,250 The primary sensory neurons are in the cochlear nerve. 772 00:44:51,250 --> 00:44:53,205 It's a bipolar cell. 773 00:44:53,205 --> 00:44:57,200 Their endings respond to the depolarization 774 00:44:57,200 --> 00:45:00,210 created in the receptors cells, which are these hair cells. 775 00:45:00,210 --> 00:45:03,320 So the hair cells are not primary sensory neurons. 776 00:45:03,320 --> 00:45:05,910 We call them receptor cells. 777 00:45:05,910 --> 00:45:13,880 But it's the depolarization of the receptor cell membrane 778 00:45:13,880 --> 00:45:15,510 at the endings there. 779 00:45:15,510 --> 00:45:17,010 They're really the dendritic endings 780 00:45:17,010 --> 00:45:19,980 of the eighth nerve cells. 781 00:45:19,980 --> 00:45:24,740 And those dendritic endings are-- their polarization 782 00:45:24,740 --> 00:45:25,650 changes. 783 00:45:25,650 --> 00:45:28,310 And you can get action potentials generated 784 00:45:28,310 --> 00:45:30,955 in those axons that travel towards the hindbrain. 785 00:45:37,890 --> 00:45:40,570 So this question is, how is a place code 786 00:45:40,570 --> 00:45:44,510 use for encoding of sound frequency? 787 00:45:44,510 --> 00:45:50,550 And it's basically because the maximum vibration 788 00:45:50,550 --> 00:45:53,590 along the basilar membrane here is 789 00:45:53,590 --> 00:45:58,335 different for sounds of different frequencies. 790 00:46:01,980 --> 00:46:04,980 The high frequencies and then the low frequencies 791 00:46:04,980 --> 00:46:05,710 stretched out. 792 00:46:05,710 --> 00:46:10,520 And if you-- history shows that in one picture. 793 00:46:10,520 --> 00:46:13,102 Here they show the unrolling of the cochlea. 794 00:46:13,102 --> 00:46:14,310 I probably should've used it. 795 00:46:14,310 --> 00:46:16,059 I don't think I used this one in the book. 796 00:46:16,059 --> 00:46:17,470 But it's a nice one. 797 00:46:17,470 --> 00:46:22,410 It shows the relative amplitude of movement 798 00:46:22,410 --> 00:46:25,670 and how it changes for different frequencies. 799 00:46:25,670 --> 00:46:32,530 So the very high frequencies vibrate the membrane best here. 800 00:46:32,530 --> 00:46:35,504 The low frequencies vibrate the membrane best here. 801 00:46:35,504 --> 00:46:37,920 You could thinking of them as standing waves, if you want. 802 00:46:37,920 --> 00:46:40,850 But all of these, of course, are very brief sounds. 803 00:46:43,620 --> 00:46:47,960 And this is from data from [INAUDIBLE], where 804 00:46:47,960 --> 00:46:52,390 you have frequency plotted here, from very low frequencies up 805 00:46:52,390 --> 00:46:55,440 to almost 5,000 Hertz. 806 00:46:55,440 --> 00:46:58,550 And he always said kilocycles. 807 00:46:58,550 --> 00:47:01,100 But we changed it to Hertz. 808 00:47:01,100 --> 00:47:04,634 And you see the different positions of maximum vibration. 809 00:47:07,640 --> 00:47:10,680 And that's how frequency is initially encoded. 810 00:47:14,580 --> 00:47:20,280 And intensity coding has got a similar kind of thing. 811 00:47:20,280 --> 00:47:21,750 But they are different. 812 00:47:21,750 --> 00:47:25,320 That's because different axons of the eighth nerve 813 00:47:25,320 --> 00:47:28,950 have different thresholds, depending on intensity. 814 00:47:28,950 --> 00:47:31,570 So that gives you, also, a place code for intensity. 815 00:47:37,060 --> 00:47:40,100 Now, if you go to the cochlear nuclei, 816 00:47:40,100 --> 00:47:44,430 as I've diagrammed here-- dorsal and ventral cochlear nuclei-- 817 00:47:44,430 --> 00:47:47,010 and you put an electrode up here in a cat, 818 00:47:47,010 --> 00:47:49,170 and you just penetrate, going straight 819 00:47:49,170 --> 00:47:52,670 down through the cochlear nuclei, 820 00:47:52,670 --> 00:47:57,090 the best frequency-- that is the frequency at which you 821 00:47:57,090 --> 00:47:59,030 can use the lowest amplitude of sound 822 00:47:59,030 --> 00:48:04,010 and get responses in a cell-- changes very systematically. 823 00:48:04,010 --> 00:48:07,680 It's a very precise representation of frequency. 824 00:48:07,680 --> 00:48:10,010 And that is interpreted this way. 825 00:48:10,010 --> 00:48:16,000 Here's the eighth nerve coming in to the ventral end 826 00:48:16,000 --> 00:48:18,190 of the ventral cochlear nucleus. 827 00:48:18,190 --> 00:48:20,530 There's the dorsal cochlear nucleus. 828 00:48:20,530 --> 00:48:27,635 And axons from different parts of the basilar membrane-- that 829 00:48:27,635 --> 00:48:32,620 is, axons picking up the contacting receptor 830 00:48:32,620 --> 00:48:35,190 cells at different positions along the basilar membrane-- 831 00:48:35,190 --> 00:48:38,570 terminate in different places, depending 832 00:48:38,570 --> 00:48:41,690 on which part of the basilar membrane they come from. 833 00:48:41,690 --> 00:48:44,120 So it's really a topography that's 834 00:48:44,120 --> 00:48:47,660 formed that's not unlike the retinal technical topography, 835 00:48:47,660 --> 00:48:54,490 except this is one-dimensional, instead of two-dimensional. 836 00:48:54,490 --> 00:48:58,890 And note that an axon representing mainly one 837 00:48:58,890 --> 00:49:04,690 frequency will terminate by forming branches that 838 00:49:04,690 --> 00:49:08,610 stay in one plane along the going dorsal-- sorry, 839 00:49:08,610 --> 00:49:10,070 rostral to caudal. 840 00:49:10,070 --> 00:49:11,620 And then it does the same thing again 841 00:49:11,620 --> 00:49:13,680 in the dorsal cochlear nucleus. 842 00:49:13,680 --> 00:49:18,040 So it does a very similar thing in the two nuclei. 843 00:49:18,040 --> 00:49:20,365 And that's how you get that topographic representation 844 00:49:20,365 --> 00:49:21,550 of sound frequencies. 845 00:49:25,270 --> 00:49:26,680 So this is just what I said. 846 00:49:33,050 --> 00:49:36,375 And what I want to do, then, is follow these channels 847 00:49:36,375 --> 00:49:39,640 of conduction through-- we're out of time. 848 00:49:39,640 --> 00:49:41,980 But I want to make a little more sense of this kind 849 00:49:41,980 --> 00:49:47,710 of diagram, of these different lemniscal channels going 850 00:49:47,710 --> 00:49:53,810 forward from the cochlear nuclei and trapezoid body, 851 00:49:53,810 --> 00:49:56,960 what's happening in the trapezoid body, 852 00:49:56,960 --> 00:50:01,270 and then what's happening to the axons going rostrally 853 00:50:01,270 --> 00:50:04,390 from these nuclei and from the trapezoid body. 854 00:50:04,390 --> 00:50:06,600 So we'll do that next time. 855 00:50:06,600 --> 00:50:13,210 And go as far as we can with the auditory system next time.