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 --> 00:00:17,271 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:17,271 --> 00:00:17,896 at ocw.mit.edu. 8 00:00:22,850 --> 00:00:24,870 PROFESSOR: Yeah, that's an exciting time 9 00:00:24,870 --> 00:00:25,930 in graduate school. 10 00:00:25,930 --> 00:00:26,544 [LAUGHTER] 11 00:00:26,544 --> 00:00:27,960 When you're finished with classes. 12 00:00:27,960 --> 00:00:30,080 AUDIENCE: I am 26 years old. 13 00:00:30,080 --> 00:00:32,960 I'm done with taking classes. 14 00:00:32,960 --> 00:00:37,016 It's all research from here. 15 00:00:37,016 --> 00:00:39,670 PROFESSOR: Look, I don't want to wait for others to show up 16 00:00:39,670 --> 00:00:43,560 because we-- as it is, we're probably short one 17 00:00:43,560 --> 00:00:46,760 class in going through all the neocortex very carefully. 18 00:00:46,760 --> 00:00:52,060 I just want to point out major things 19 00:00:52,060 --> 00:00:53,560 that I think you need to know. 20 00:00:56,100 --> 00:01:00,080 When we talk about radial vesicles in the neocortex 21 00:01:00,080 --> 00:01:01,930 we just mean these. 22 00:01:01,930 --> 00:01:04,660 You see on the previous picture here? 23 00:01:04,660 --> 00:01:07,390 These are the slides from last time. 24 00:01:07,390 --> 00:01:09,080 We started last time here. 25 00:01:09,080 --> 00:01:11,220 These are the radial vesicles. 26 00:01:11,220 --> 00:01:16,840 These are transverse groups of axons. 27 00:01:16,840 --> 00:01:20,850 So what kind of axon has to be in there? 28 00:01:20,850 --> 00:01:22,070 That's what I'm asking you. 29 00:01:22,070 --> 00:01:24,680 And if you've learned a bit about neuronanatomy 30 00:01:24,680 --> 00:01:27,850 you shouldn't have to even look at the book. 31 00:01:27,850 --> 00:01:31,170 They've got to be thalamocorticals. 32 00:01:31,170 --> 00:01:32,845 They're terminating in all the layers, 33 00:01:32,845 --> 00:01:35,030 but especially in layer 4 when you 34 00:01:35,030 --> 00:01:39,200 see the layers numbered out here. 35 00:01:39,200 --> 00:01:40,110 All right. 36 00:01:40,110 --> 00:01:42,650 And what else do they include? 37 00:01:42,650 --> 00:01:44,830 Well, various outputs. 38 00:01:44,830 --> 00:01:47,990 There are outputs to the brain stem 39 00:01:47,990 --> 00:01:50,490 that are coming from layer 5. 40 00:01:50,490 --> 00:01:53,350 There are outputs to the thalamus coming from layer 6. 41 00:01:53,350 --> 00:01:56,350 And there's outputs to other areas of cortex 42 00:01:56,350 --> 00:01:59,850 coming from layer 2 and 3. 43 00:01:59,850 --> 00:02:03,830 So that's what makes up those radial vesicles. 44 00:02:03,830 --> 00:02:08,169 In fact, there's also some intracolumnar axons. 45 00:02:08,169 --> 00:02:13,475 But most of those are probably not in the radial vesicles 46 00:02:13,475 --> 00:02:17,580 but axons that have so little myelin that you don't really 47 00:02:17,580 --> 00:02:19,835 see them in this myelin stain. 48 00:02:22,950 --> 00:02:26,670 So I just summarized that in the following slides here. 49 00:02:26,670 --> 00:02:29,050 And I mentioned the line of Gennari. 50 00:02:29,050 --> 00:02:32,180 It's a sort of historical point, but it's an interesting one 51 00:02:32,180 --> 00:02:39,350 because it refers to one of these-- this one. 52 00:02:39,350 --> 00:02:41,660 This transverse group of axons we 53 00:02:41,660 --> 00:02:45,500 can see here on the picture from Rodale 54 00:02:45,500 --> 00:02:48,740 and there's a similar one in the book. 55 00:02:48,740 --> 00:02:52,140 So just mention what that is there. 56 00:02:52,140 --> 00:02:55,730 If you look at the-- you can actually see it in a dissection 57 00:02:55,730 --> 00:02:58,390 if you make a slice through the visual cortex. 58 00:02:58,390 --> 00:03:01,340 You see this light area. 59 00:03:01,340 --> 00:03:03,710 And I'll mark it here. 60 00:03:03,710 --> 00:03:06,705 This is in a young human brain. 61 00:03:06,705 --> 00:03:09,630 It's actually a little clearer. 62 00:03:09,630 --> 00:03:17,490 The purpose of these slides was to show the distinct nature 63 00:03:17,490 --> 00:03:19,970 of the cytoarchitecture of these different regions. 64 00:03:19,970 --> 00:03:22,870 And the clearest boundary in all the cortex 65 00:03:22,870 --> 00:03:26,380 is the boundary between area 17 and 18. 66 00:03:26,380 --> 00:03:30,120 17 on the left here, 18 on the right. 67 00:03:30,120 --> 00:03:33,120 This is in a myelin stain. 68 00:03:33,120 --> 00:03:39,050 Well, you see, again, big difference in the left side, 69 00:03:39,050 --> 00:03:41,850 which is area 17, and the right side, which is area 18. 70 00:03:41,850 --> 00:03:47,380 And in the middle of 17 you have all these axons. 71 00:03:47,380 --> 00:03:50,190 So they have to be mostly transverse axons. 72 00:03:50,190 --> 00:03:54,540 Some short association axons and perhaps some longer ones 73 00:03:54,540 --> 00:03:58,610 that go from one part of area 17 to others. 74 00:03:58,610 --> 00:03:59,880 And this is from the adult. 75 00:03:59,880 --> 00:04:03,120 And here I've numbered in the Nissl stain the layers for you. 76 00:04:03,120 --> 00:04:07,500 You see that here-- this is Gennari's line here, 77 00:04:07,500 --> 00:04:12,350 the axons in the middle of layer 4. 78 00:04:12,350 --> 00:04:15,220 So there's a lot of granule cells on either side of it. 79 00:04:17,940 --> 00:04:21,100 And there you see-- these are corresponding pictures. 80 00:04:21,100 --> 00:04:23,810 This is the myelin where you see those-- 81 00:04:23,810 --> 00:04:28,540 that stripe of Gennari, named after the medical student who 82 00:04:28,540 --> 00:04:34,100 first noticed it, called attention to it. 83 00:04:34,100 --> 00:04:38,210 So now let's talk about the specialized cortical columns. 84 00:04:38,210 --> 00:04:40,460 We used to think they were mainly 85 00:04:40,460 --> 00:04:45,110 in places like visual cortex where the two eyes are 86 00:04:45,110 --> 00:04:49,690 represented in adjacent stripes or columns of cortex. 87 00:04:49,690 --> 00:04:50,880 So how was that visualized? 88 00:04:50,880 --> 00:04:52,400 Do you remember? 89 00:04:52,400 --> 00:04:57,385 The injected a tracer right into the eyeball. 90 00:04:57,385 --> 00:04:59,860 It was taken up by the retinal ganglion cells. 91 00:04:59,860 --> 00:05:04,920 And then they use a tracer like proline that will go 92 00:05:04,920 --> 00:05:08,250 [INAUDIBLE] So it reaches the geniculate body. 93 00:05:08,250 --> 00:05:11,980 It gets taken up by the cells in the geniculate, which then it's 94 00:05:11,980 --> 00:05:14,520 transferred up to the-- transported up 95 00:05:14,520 --> 00:05:15,890 to the visual cortex. 96 00:05:15,890 --> 00:05:19,630 And if you do a tangential sections of the cortex 97 00:05:19,630 --> 00:05:22,940 and put together different sections, 98 00:05:22,940 --> 00:05:26,650 you can get a picture like this that shows that zebra stripe 99 00:05:26,650 --> 00:05:28,520 pattern. 100 00:05:28,520 --> 00:05:33,764 The light stripes here are the labeled ones from one eye. 101 00:05:33,764 --> 00:05:35,940 And if you had labeled both eyes, 102 00:05:35,940 --> 00:05:38,430 it would be totally white. 103 00:05:38,430 --> 00:05:41,540 But there the other eye projects to the in between stripes 104 00:05:41,540 --> 00:05:43,020 there. 105 00:05:43,020 --> 00:05:48,840 But it turns out that columnar types of termination of axons 106 00:05:48,840 --> 00:05:51,870 is very common in the cortex. 107 00:05:51,870 --> 00:05:58,150 Nauta, and this is-- he worked with Pat Goldman. 108 00:05:58,150 --> 00:06:01,890 She came up here to his lab and learned some of the techniques 109 00:06:01,890 --> 00:06:03,280 for tracing. 110 00:06:03,280 --> 00:06:05,220 And this is from a study they did together 111 00:06:05,220 --> 00:06:08,820 where they were tracing prefrontal association area 112 00:06:08,820 --> 00:06:13,825 projections to more posterior parts of the cortex. 113 00:06:13,825 --> 00:06:16,393 And they traced them here to the retrosplenial area 114 00:06:16,393 --> 00:06:18,000 of the cortex. 115 00:06:18,000 --> 00:06:20,550 And you'll see this termination in stripes. 116 00:06:23,440 --> 00:06:25,310 And I just point out here at the top, 117 00:06:25,310 --> 00:06:29,130 I wrote this morning-- columnar patterns of axon termination 118 00:06:29,130 --> 00:06:33,305 are a common feature of many inputs to neocortical areas. 119 00:06:33,305 --> 00:06:37,540 Many of the transcortical projections 120 00:06:37,540 --> 00:06:39,370 are like this, where you have more than one 121 00:06:39,370 --> 00:06:43,180 transcortical input coming in to the same area. 122 00:06:43,180 --> 00:06:46,670 And some of them are also-- the callosal projections 123 00:06:46,670 --> 00:06:51,090 also terminate in this matter, indicating 124 00:06:51,090 --> 00:06:53,750 some kind of integration of these two different inputs. 125 00:06:57,680 --> 00:07:00,090 Now we've talked a number of different times 126 00:07:00,090 --> 00:07:01,470 about major types of cortex. 127 00:07:04,100 --> 00:07:06,200 First of all, the major types are 128 00:07:06,200 --> 00:07:11,720 neocortex and the other cortex and the in between ones. 129 00:07:11,720 --> 00:07:14,220 Paralimbic areas are often-- sometimes 130 00:07:14,220 --> 00:07:17,240 people call them neocortex. 131 00:07:17,240 --> 00:07:22,080 Most people just call them juxtalo cortex. 132 00:07:25,290 --> 00:07:29,000 Transitional areas between neocortex and limbic system 133 00:07:29,000 --> 00:07:30,660 structures. 134 00:07:30,660 --> 00:07:33,000 So those are the three major types. 135 00:07:33,000 --> 00:07:38,480 But within those types now, there are different regions. 136 00:07:38,480 --> 00:07:40,120 We know about Broca's areas. 137 00:07:40,120 --> 00:07:42,600 They are all different areas in the neocortex 138 00:07:42,600 --> 00:07:44,090 and he did it by cytoarchitecture 139 00:07:44,090 --> 00:07:45,430 with Nissl stains. 140 00:07:49,250 --> 00:07:51,170 You can also use major connections 141 00:07:51,170 --> 00:07:53,520 as for grouping them. 142 00:07:53,520 --> 00:07:55,430 So let's look at examples of that. 143 00:07:55,430 --> 00:07:58,700 If you just use connections, as Mesulam 144 00:07:58,700 --> 00:08:01,560 was doing when he grouped the paralimbic areas, 145 00:08:01,560 --> 00:08:07,670 you see one group-- I probably showed this before-- one group 146 00:08:07,670 --> 00:08:10,270 that projects to parahippocampal area. 147 00:08:10,270 --> 00:08:14,470 So it's sending information towards the hippocampus. 148 00:08:14,470 --> 00:08:18,670 And the other group-- and together 149 00:08:18,670 --> 00:08:22,840 they constitute the entire limbic lobe-- 150 00:08:22,840 --> 00:08:26,590 the other area is darker in his picture here. 151 00:08:26,590 --> 00:08:28,240 They use different colors in the book, 152 00:08:28,240 --> 00:08:33,640 but I used a-- I based my figure on the Mesulam picture. 153 00:08:37,601 --> 00:08:38,850 He calls them olfacto-centric. 154 00:08:41,700 --> 00:08:43,850 There would be different ways to name it, 155 00:08:43,850 --> 00:08:48,540 but they tend to project to areas that are closely related 156 00:08:48,540 --> 00:08:50,960 to olfactory system. 157 00:08:50,960 --> 00:08:54,900 To the amygdala, to the basal forebrain. 158 00:08:54,900 --> 00:08:58,430 And they project to areas involved 159 00:08:58,430 --> 00:09:06,680 in the-- you could say the limbic tags-- 160 00:09:06,680 --> 00:09:11,990 the emotions associated with objects. 161 00:09:11,990 --> 00:09:14,550 So always concerned with the object information. 162 00:09:14,550 --> 00:09:16,160 Whereas the hippocampus-centric is 163 00:09:16,160 --> 00:09:18,250 more concerned with place information. 164 00:09:18,250 --> 00:09:21,610 So that's a way to group cortical regions 165 00:09:21,610 --> 00:09:23,040 on the basis of connections. 166 00:09:23,040 --> 00:09:27,090 And it's convenient to group the paralimbic areas that way, 167 00:09:27,090 --> 00:09:29,770 those transitional areas. 168 00:09:29,770 --> 00:09:32,340 These are areas that get a lot of inputs 169 00:09:32,340 --> 00:09:35,130 from association areas of the neocortex 170 00:09:35,130 --> 00:09:39,900 and they're all connected to deeper lying limbic system 171 00:09:39,900 --> 00:09:45,770 structures like the amygdala and the hippocampus. 172 00:09:45,770 --> 00:09:49,610 So whereas within the neocortex now, 173 00:09:49,610 --> 00:09:52,310 we see structural differences. 174 00:09:52,310 --> 00:09:55,530 The extremes are shown at the two ends 175 00:09:55,530 --> 00:10:00,395 in this picture based on von Economo, who, 176 00:10:00,395 --> 00:10:04,090 like Brodmann, did a like of cytoarchitectural work 177 00:10:04,090 --> 00:10:08,640 on the human brain, as well as other animals. 178 00:10:08,640 --> 00:10:12,420 And he's showing primary sensory at this end. 179 00:10:12,420 --> 00:10:15,590 And so just look at layer 4 here, 180 00:10:15,590 --> 00:10:18,660 where you see the granule cells. 181 00:10:18,660 --> 00:10:21,000 And then look at the other extreme. 182 00:10:21,000 --> 00:10:23,370 Primary motor cortex. 183 00:10:23,370 --> 00:10:26,070 It's agranular. 184 00:10:26,070 --> 00:10:28,880 When you get to the layer 4 region, 185 00:10:28,880 --> 00:10:32,430 it doesn't really look much different from the layers 186 00:10:32,430 --> 00:10:33,955 above and below it because there's 187 00:10:33,955 --> 00:10:37,170 many pyramidal cells and not so many granule cells. 188 00:10:37,170 --> 00:10:40,070 So it doesn't form a distinct layer. 189 00:10:40,070 --> 00:10:46,350 But that's only in agranular cortex, the motor areas. 190 00:10:46,350 --> 00:10:50,970 And then you have other areas, prefrontal types 191 00:10:50,970 --> 00:10:56,260 of cortex, parietal types, and the polar types-- frontal pole, 192 00:10:56,260 --> 00:10:59,140 temporal pole, which are a little different. 193 00:10:59,140 --> 00:11:00,860 But they still have-- it's always 194 00:11:00,860 --> 00:11:03,176 possible to name the six layers. 195 00:11:03,176 --> 00:11:04,800 The only places that would be difficult 196 00:11:04,800 --> 00:11:07,010 is in the motor cortical areas. 197 00:11:09,670 --> 00:11:14,500 So let's say a little more about these layer 4 extremes. 198 00:11:14,500 --> 00:11:17,790 Biggest differences are between the primary visual cortex 199 00:11:17,790 --> 00:11:21,830 and the primary motor cortex, where-- 200 00:11:21,830 --> 00:11:25,300 so that's what I was just talking about. 201 00:11:25,300 --> 00:11:26,440 The layer 4 differences. 202 00:11:26,440 --> 00:11:28,880 And we saw area 17 earlier. 203 00:11:28,880 --> 00:11:31,450 Well, you see how prominent, even 204 00:11:31,450 --> 00:11:35,890 more than in the von Economo picture here, 205 00:11:35,890 --> 00:11:37,940 extremely prominent layer 4 is. 206 00:11:37,940 --> 00:11:39,275 And it can be subdivided. 207 00:11:39,275 --> 00:11:43,170 It's normally subdivided in primates into three sublayers, 208 00:11:43,170 --> 00:11:47,340 and then in addition it has those transverse fibers, 209 00:11:47,340 --> 00:11:48,260 the line of Gennari. 210 00:11:51,960 --> 00:11:54,950 And we've talked about connectional differences. 211 00:11:54,950 --> 00:11:58,280 In this diagram, I take the cell bodies 212 00:11:58,280 --> 00:12:00,440 in these different layers and show 213 00:12:00,440 --> 00:12:05,970 how the axon from both cell bodies, the prominent direction 214 00:12:05,970 --> 00:12:08,550 of axon outflow from those layers-- 215 00:12:08,550 --> 00:12:12,510 it's based on this picture which we saw earlier, which 216 00:12:12,510 --> 00:12:20,140 shows a slightly expanded view of major connections within one 217 00:12:20,140 --> 00:12:23,450 cortical column. 218 00:12:23,450 --> 00:12:25,785 It shows the different association types 219 00:12:25,785 --> 00:12:28,050 of axons, as well as projection axons. 220 00:12:30,640 --> 00:12:34,520 So it's useful to know these. 221 00:12:34,520 --> 00:12:39,880 These represent the thalamalcortical axons, 222 00:12:39,880 --> 00:12:43,420 like to a sensory area coming primarily 223 00:12:43,420 --> 00:12:49,080 to layer 4, but also layers 1 and 6 and a little bit less 224 00:12:49,080 --> 00:12:50,575 to the other layers. 225 00:12:50,575 --> 00:12:53,370 It does go to all of the layers, but these 226 00:12:53,370 --> 00:12:55,480 are the dense projections. 227 00:12:55,480 --> 00:12:57,590 And that densest projection to layer 4, 228 00:12:57,590 --> 00:13:00,750 you can see the information goes from layer 4 229 00:13:00,750 --> 00:13:06,140 primarily up by means of the excitatory interneurons, 230 00:13:06,140 --> 00:13:09,954 these little stellate cells that have axons that just project 231 00:13:09,954 --> 00:13:11,620 towards the [INAUDIBLE] surface and they 232 00:13:11,620 --> 00:13:13,620 terminate in layers 2 and 3. 233 00:13:13,620 --> 00:13:19,870 And those layers project heavily to layer 5 in addition 234 00:13:19,870 --> 00:13:22,220 to having association connections 235 00:13:22,220 --> 00:13:24,540 to other cortical areas I'm not showing those. 236 00:13:24,540 --> 00:13:28,720 I'm just showing the intracolumnar connections here. 237 00:13:28,720 --> 00:13:35,850 And 5 projects to 6 and 6 and 5 both have some feedback 238 00:13:35,850 --> 00:13:38,810 connections to the more superficial layers. 239 00:13:38,810 --> 00:13:42,750 And this-- we used this one before, 240 00:13:42,750 --> 00:13:44,640 this picture of a cortical column, 241 00:13:44,640 --> 00:13:50,880 to talk about the different types of transverse connections 242 00:13:50,880 --> 00:13:54,500 in cortex within the layers. 243 00:13:54,500 --> 00:13:59,960 In layer one, in layer 4 primarily. 244 00:13:59,960 --> 00:14:05,240 And then transcortically by U-fibers to other areas. 245 00:14:05,240 --> 00:14:07,630 I show one here coming from layer 2. 246 00:14:07,630 --> 00:14:11,750 Layer 3 cells would have many connections like that also. 247 00:14:11,750 --> 00:14:17,550 And then layers 5 and 6 going to subcortical areas. 248 00:14:17,550 --> 00:14:20,980 Corpus striatum, thalamus, brain stem. 249 00:14:20,980 --> 00:14:24,255 The ones to the thalamus come from layer 6. 250 00:14:26,930 --> 00:14:31,090 Another way to look at those layer 4 extremes 251 00:14:31,090 --> 00:14:33,410 is an interesting one of comparison 252 00:14:33,410 --> 00:14:36,755 made by Brian Cragin, electron microscope studies. 253 00:14:36,755 --> 00:14:39,780 He just looked at total number of synapses per cell. 254 00:14:39,780 --> 00:14:44,300 Just take a little column of cortex, 255 00:14:44,300 --> 00:14:46,850 do the same for visual cortex and motor cortex. 256 00:14:46,850 --> 00:14:49,360 He did it for rats and for monkeys. 257 00:14:49,360 --> 00:14:52,240 And this is for the monkey. 258 00:14:52,240 --> 00:14:59,440 And he counted the synapses and counted the cell bodies, 259 00:14:59,440 --> 00:15:02,190 the neuronal cell bodies. 260 00:15:02,190 --> 00:15:06,360 He found about 4,000 synapses per neuron 261 00:15:06,360 --> 00:15:08,470 in the primary visual cortex. 262 00:15:08,470 --> 00:15:13,290 But in area 4, the primary motor cortex, he found 60,000. 263 00:15:13,290 --> 00:15:16,150 What does that indicate? 264 00:15:16,150 --> 00:15:22,970 A lot of-- much more convergence in the motor cortex coming 265 00:15:22,970 --> 00:15:27,500 from various sources into those neurons in the motor cortex. 266 00:15:30,880 --> 00:15:32,490 And I mentioned the different kind-- 267 00:15:32,490 --> 00:15:34,470 where those synapses-- the kind of axon 268 00:15:34,470 --> 00:15:38,720 that is synapsing on those cells. 269 00:15:38,720 --> 00:15:42,820 I ask here, what are probably the dominant ones in area 17? 270 00:15:42,820 --> 00:15:45,940 We always think of the thalamalcorticals for area 17. 271 00:15:45,940 --> 00:15:49,130 And, yes, many synapses are like that. 272 00:15:49,130 --> 00:15:55,470 But I think you have to ask about those synapses 273 00:15:55,470 --> 00:15:57,680 formed by the axons in the line of Gennari, 274 00:15:57,680 --> 00:16:00,450 the transverse axons, because they probably 275 00:16:00,450 --> 00:16:03,580 contribute large numbers of terminals as well. 276 00:16:06,310 --> 00:16:11,210 Let's look briefly at the functional types and talk 277 00:16:11,210 --> 00:16:12,415 about Brodmann's areas. 278 00:16:16,180 --> 00:16:18,250 First of all, about functional types. 279 00:16:18,250 --> 00:16:22,310 We usually talk about primary sensory, primary motor, 280 00:16:22,310 --> 00:16:24,290 association, and limbic areas. 281 00:16:24,290 --> 00:16:28,750 I like Mesulam's view, which is very similar. 282 00:16:28,750 --> 00:16:37,550 But he talks about the idiotypic cortex as the most specialized. 283 00:16:37,550 --> 00:16:40,669 That's primary sensory and primary motor. 284 00:16:40,669 --> 00:16:42,460 There are the areas that are most different 285 00:16:42,460 --> 00:16:43,910 from other areas. 286 00:16:43,910 --> 00:16:47,630 So that's one type in his nomenclature. 287 00:16:47,630 --> 00:16:49,780 Primary sensory or motor. 288 00:16:49,780 --> 00:16:52,940 And then he divides the association cortex unimodal, 289 00:16:52,940 --> 00:16:59,280 or primarily unimodal, and the multimodal areas. 290 00:16:59,280 --> 00:17:01,485 And then finally, you have the limbic areas. 291 00:17:04,000 --> 00:17:06,819 Now Brodmann used Nissl methods to divide up 292 00:17:06,819 --> 00:17:09,810 all of the neocortex and this is the map. 293 00:17:09,810 --> 00:17:13,660 And what I did here-- you'd have to enlarge this quite a bit 294 00:17:13,660 --> 00:17:15,540 to actually see his numbers. 295 00:17:15,540 --> 00:17:19,339 What I've done is I've put red dots by the areas 296 00:17:19,339 --> 00:17:22,060 that basically all anatomists know. 297 00:17:25,829 --> 00:17:28,990 The others, we often just talk about the region, 298 00:17:28,990 --> 00:17:33,110 like the various temporal regions, prefrontal regions, 299 00:17:33,110 --> 00:17:38,310 areas of locus cortex here, and the inferior prefrontal cortex 300 00:17:38,310 --> 00:17:40,120 and premotor cortex. 301 00:17:40,120 --> 00:17:42,180 So what are these areas I've marked? 302 00:17:42,180 --> 00:17:47,550 Well, 17, 18, and 19 in the visual areas. 303 00:17:47,550 --> 00:17:50,396 That is the primary visual cortex, 17. 304 00:17:50,396 --> 00:17:53,820 18 and 19, which are unimodal association 305 00:17:53,820 --> 00:17:55,720 areas of the visual system. 306 00:17:55,720 --> 00:18:00,405 There are additional ones, but-- because the visual system 307 00:18:00,405 --> 00:18:05,410 in primates has expanded so much into the temporal lobe. 308 00:18:05,410 --> 00:18:07,440 And then here in somatosensory. 309 00:18:07,440 --> 00:18:10,540 Primary somatosensory areas-- 3, 1, and 2. 310 00:18:10,540 --> 00:18:12,400 Those are the Brodmann numbers. 311 00:18:12,400 --> 00:18:17,690 And then in the motor cortex, area 4 312 00:18:17,690 --> 00:18:19,800 is the primary motor cortex. 313 00:18:19,800 --> 00:18:24,020 And right in front of it, area 6, that's the premotor cortex. 314 00:18:24,020 --> 00:18:26,280 These are the areas that get the projections 315 00:18:26,280 --> 00:18:29,250 from the ventrolateral nucleus and the ventral anterior 316 00:18:29,250 --> 00:18:30,490 nucleus. 317 00:18:30,490 --> 00:18:33,170 Area 4 and area 6. 318 00:18:33,170 --> 00:18:36,000 And then people usually know what area 8 is. 319 00:18:36,000 --> 00:18:38,410 It's the frontal eye fields. 320 00:18:38,410 --> 00:18:41,950 Gets input from visual system. 321 00:18:41,950 --> 00:18:46,620 Site of working memory for positions 322 00:18:46,620 --> 00:18:50,180 and egocentric positions around our head. 323 00:18:50,180 --> 00:18:52,450 We retain the information, at least briefly. 324 00:18:52,450 --> 00:18:56,900 It's used in making decisions about where to move our eyes. 325 00:18:56,900 --> 00:18:59,591 Makes the saccadic eye movements. 326 00:18:59,591 --> 00:19:03,910 Voluntary movements of the eyes. 327 00:19:03,910 --> 00:19:06,230 Probably not the involuntary saccades, 328 00:19:06,230 --> 00:19:08,510 but the voluntary ones. 329 00:19:12,640 --> 00:19:15,220 So when we come to functional differences, what 330 00:19:15,220 --> 00:19:17,740 are the methods that people have used? 331 00:19:17,740 --> 00:19:21,310 Just summarize them. 332 00:19:21,310 --> 00:19:22,310 What do you remember? 333 00:19:22,310 --> 00:19:24,710 What have people done? 334 00:19:24,710 --> 00:19:26,592 We're talking about function. 335 00:19:26,592 --> 00:19:27,175 They've used-- 336 00:19:27,175 --> 00:19:28,681 AUDIENCE: [INAUDIBLE]. 337 00:19:28,681 --> 00:19:29,580 PROFESSOR: Sorry? 338 00:19:29,580 --> 00:19:31,080 AUDIENCE: Stimulation. 339 00:19:31,080 --> 00:19:33,760 PROFESSOR: Stimulation and recording. 340 00:19:33,760 --> 00:19:35,920 The electrophysiological methods. 341 00:19:35,920 --> 00:19:37,550 Those are major methods that have 342 00:19:37,550 --> 00:19:39,850 been used a long, long time in neuroscience 343 00:19:39,850 --> 00:19:42,410 to specify the function. 344 00:19:42,410 --> 00:19:46,330 It does the best for sensory areas. 345 00:19:46,330 --> 00:19:48,710 And motor areas they've used more electrical stimulation. 346 00:19:51,950 --> 00:19:53,720 What other method? 347 00:19:53,720 --> 00:19:55,305 AUDIENCE: [INAUDIBLE]. 348 00:19:55,305 --> 00:19:56,550 PROFESSOR: Lesions. 349 00:19:56,550 --> 00:19:57,110 Exactly. 350 00:19:57,110 --> 00:19:59,030 Ablation results. 351 00:19:59,030 --> 00:20:03,620 We make them in animals under-- we 352 00:20:03,620 --> 00:20:06,100 know where the different areas are in an animal 353 00:20:06,100 --> 00:20:09,232 and we specifically try to ablade very specific areas 354 00:20:09,232 --> 00:20:10,690 to work out functional differences. 355 00:20:10,690 --> 00:20:15,900 In humans it's people that have had strokes or gunshot wounds 356 00:20:15,900 --> 00:20:23,460 or other traumatic injury to the cortex. 357 00:20:23,460 --> 00:20:25,740 And that has all contribute-- all of those methods 358 00:20:25,740 --> 00:20:29,510 have contributed a lot to our knowing functional differences. 359 00:20:29,510 --> 00:20:30,814 And what's the newer method? 360 00:20:30,814 --> 00:20:31,730 AUDIENCE: [INAUDIBLE]. 361 00:20:31,730 --> 00:20:36,515 PROFESSOR: The functional imaging methods. 362 00:20:36,515 --> 00:20:40,020 PET scanning and magnetic resonance imaging. 363 00:20:40,020 --> 00:20:42,790 Primarily magnetic resonance imaging. 364 00:20:42,790 --> 00:20:47,710 And now, of course also, magnetoencephalography is used. 365 00:20:47,710 --> 00:20:51,070 These are all techniques you can use live people, 366 00:20:51,070 --> 00:20:54,380 as well as live animals. 367 00:20:54,380 --> 00:20:58,130 So this is just-- I want to review temporalization briefly, 368 00:20:58,130 --> 00:20:59,140 show you one more thing. 369 00:20:59,140 --> 00:21:00,843 And then axons to and from neocortex. 370 00:21:04,620 --> 00:21:09,010 We've talked about the big neocortical expansion 371 00:21:09,010 --> 00:21:11,610 we call temporalization. 372 00:21:11,610 --> 00:21:14,660 If you take a rodent brain here and compare it 373 00:21:14,660 --> 00:21:16,192 to these other three branches, you 374 00:21:16,192 --> 00:21:19,520 see enormous amount of cortex in the temporal lobe 375 00:21:19,520 --> 00:21:24,390 here because this area here has expanded so much. 376 00:21:24,390 --> 00:21:29,440 It's just-- it's done that. 377 00:21:29,440 --> 00:21:39,380 So what I did here is I've shown positions of 17 and 18, 378 00:21:39,380 --> 00:21:42,400 the oldest visual areas. 379 00:21:42,400 --> 00:21:48,820 And then, can you see my-- looks like it's a yellow there. 380 00:21:48,820 --> 00:21:52,550 I show this huge expansion of visual cortex 381 00:21:52,550 --> 00:21:57,690 there into the temporal lobe going all the way down there. 382 00:21:57,690 --> 00:22:01,600 And going in here into the parietal cortex, posterior 383 00:22:01,600 --> 00:22:05,070 parietal, down into the-- this is 384 00:22:05,070 --> 00:22:09,660 infratemporal gyrus, the infratemporal cortex. 385 00:22:09,660 --> 00:22:12,800 The equivalent areas in the rat, some of them 386 00:22:12,800 --> 00:22:14,790 have been found only fairly recently. 387 00:22:14,790 --> 00:22:16,210 So here's 17. 388 00:22:16,210 --> 00:22:21,290 This they call 18a in the rat or mouse or hamster. 389 00:22:21,290 --> 00:22:26,140 It's actually several different areas. 390 00:22:26,140 --> 00:22:29,240 So it's actually not a single area. 391 00:22:29,240 --> 00:22:33,240 So it's not totally equivalent, even though it's always 392 00:22:33,240 --> 00:22:34,180 pictured that way. 393 00:22:34,180 --> 00:22:36,990 It's really not equivalent to area 18 394 00:22:36,990 --> 00:22:40,090 in primates the primates or in the cat 395 00:22:40,090 --> 00:22:43,505 because it's multiple areas, all with separate representations 396 00:22:43,505 --> 00:22:46,710 of the visual field, not a single one. 397 00:22:46,710 --> 00:22:47,955 So that's one difference. 398 00:22:47,955 --> 00:22:50,510 And the other thing is, the area here 399 00:22:50,510 --> 00:22:56,150 I've put the orange line around or yellow-orange line is 400 00:22:56,150 --> 00:23:00,160 the area-- the only area that we know of in the rodent that's 401 00:23:00,160 --> 00:23:05,170 equivalent to this expanded area in the primates. 402 00:23:05,170 --> 00:23:09,070 It contains the postrhinal cortex, 403 00:23:09,070 --> 00:23:10,880 an area that's really parahippocampal. 404 00:23:10,880 --> 00:23:15,000 It projects pretty directly into the hippocampus. 405 00:23:15,000 --> 00:23:19,840 And the perirhinal cortex right next to the olfactory cortex. 406 00:23:23,340 --> 00:23:27,760 Those are all areas that you do find in these larger brains 407 00:23:27,760 --> 00:23:28,270 as well. 408 00:23:31,920 --> 00:23:34,470 Now let's just review something. 409 00:23:34,470 --> 00:23:37,500 I want to know about axons coming 410 00:23:37,500 --> 00:23:39,820 from somatasensory and motor areas. 411 00:23:39,820 --> 00:23:43,190 They go all the way to the spinal cord. 412 00:23:43,190 --> 00:23:49,650 These are the longest axons coming out of neocortex, 413 00:23:49,650 --> 00:23:53,660 even in animals like a rat or a mouse. 414 00:23:56,730 --> 00:23:58,250 You should be able to name them. 415 00:23:58,250 --> 00:24:00,295 We've done this before the midterm 416 00:24:00,295 --> 00:24:03,842 and you should still remember this. 417 00:24:03,842 --> 00:24:07,300 This is the picture we showed earlier. 418 00:24:07,300 --> 00:24:10,270 And I show axons coming out of the cortex, 419 00:24:10,270 --> 00:24:12,140 going through the internal capsule, 420 00:24:12,140 --> 00:24:14,760 and they become the cerebral peduncle 421 00:24:14,760 --> 00:24:19,040 along the sides of the diencepalon in this region. 422 00:24:19,040 --> 00:24:22,330 And then they become the pyramidal tract 423 00:24:22,330 --> 00:24:24,200 after passing through the pons. 424 00:24:24,200 --> 00:24:27,400 And then they're just called corticospinal tract axons 425 00:24:27,400 --> 00:24:32,370 when they're inside the spinal cord. 426 00:24:32,370 --> 00:24:35,740 And we also use this name corona radiata. 427 00:24:35,740 --> 00:24:38,150 So here when they're coming out of the cortex-- 428 00:24:38,150 --> 00:24:40,840 and they have this in a dissection. 429 00:24:40,840 --> 00:24:45,140 You can see this radiating pattern of axons. 430 00:24:45,140 --> 00:24:49,510 That's the white in the white matter, the thick white matter 431 00:24:49,510 --> 00:24:50,962 of the cerebral hemispheres. 432 00:24:50,962 --> 00:24:55,720 They're called the corona radiata. 433 00:24:55,720 --> 00:24:58,610 And those funnel into the internal capsule, 434 00:24:58,610 --> 00:25:02,490 which is what the axons are called when they're 435 00:25:02,490 --> 00:25:04,670 within the corpus striatum or going 436 00:25:04,670 --> 00:25:06,140 through the corpus striatum. 437 00:25:06,140 --> 00:25:09,310 They're called the internal capsule. 438 00:25:09,310 --> 00:25:13,120 They're encapsulated by the corpus striatum. 439 00:25:13,120 --> 00:25:16,140 And then they become-- same axons-- 440 00:25:16,140 --> 00:25:21,330 become cerebral peduncle when they're further down going 441 00:25:21,330 --> 00:25:24,750 alongside the diencephelon. 442 00:25:24,750 --> 00:25:30,280 And then they become-- we can keep calling them peduncle 443 00:25:30,280 --> 00:25:32,470 when they're at the base of the midbrain. 444 00:25:32,470 --> 00:25:35,930 Then we change the name after they go through the pons. 445 00:25:35,930 --> 00:25:38,900 So what's the difference in the axons of the cerebral peduncle 446 00:25:38,900 --> 00:25:42,790 and the axons of the pyramidal tract? 447 00:25:42,790 --> 00:25:46,130 What's missing when you get caudal to the pons? 448 00:25:46,130 --> 00:25:48,610 Well, all the cortical pontine fibers have terminated 449 00:25:48,610 --> 00:25:50,430 and there's huge numbers of them. 450 00:25:50,430 --> 00:25:53,990 So it's a lot smaller now. 451 00:25:53,990 --> 00:25:57,130 You could ask the same question about internal capsule 452 00:25:57,130 --> 00:26:00,420 versus the peduncle at the base of the midbrain. 453 00:26:00,420 --> 00:26:02,970 Well, all the fibers terminating in the tweenbrain 454 00:26:02,970 --> 00:26:06,260 are gone now unless they're branches. 455 00:26:11,580 --> 00:26:16,000 So that's all just one of the major axon bundles leading 456 00:26:16,000 --> 00:26:19,690 into and out of the mammalian forebrain. 457 00:26:19,690 --> 00:26:21,350 What is the other one? 458 00:26:21,350 --> 00:26:24,176 This is all lateral forebrain bundle. 459 00:26:24,176 --> 00:26:26,050 The other one is the medial forebrain bundle. 460 00:26:26,050 --> 00:26:28,120 And these are the pictures we had. 461 00:26:28,120 --> 00:26:31,700 So all of those axons we were just talking about 462 00:26:31,700 --> 00:26:34,200 are lateral forebrain bundle axons. 463 00:26:34,200 --> 00:26:37,000 They do include some axons from the corpus striatum that 464 00:26:37,000 --> 00:26:42,950 don't go anywhere near as far as the ones from cortex. 465 00:26:42,950 --> 00:26:47,560 The corpus striatum fibers reach-- the longest ones 466 00:26:47,560 --> 00:26:50,000 get to the caudal midbrain. 467 00:26:50,000 --> 00:26:53,197 That midbrain locomotor region and midbrain extrapyramidal 468 00:26:53,197 --> 00:26:54,360 region. 469 00:26:54,360 --> 00:26:59,880 [INAUDIBLE] in the midbrain in the reticular formation. 470 00:26:59,880 --> 00:27:03,880 So these are those pictures that show those two major bundles. 471 00:27:03,880 --> 00:27:06,005 And I named the components here. 472 00:27:13,970 --> 00:27:15,010 Thought I opened this. 473 00:27:19,920 --> 00:27:25,760 So let's talk more about thalamalcortical organization 474 00:27:25,760 --> 00:27:30,240 and transcortical connections and association cortex. 475 00:27:30,240 --> 00:27:33,460 And then at the end about thalamic evolution, which 476 00:27:33,460 --> 00:27:35,230 we might not get to in class, but it just 477 00:27:35,230 --> 00:27:39,835 summarizes for you things that I talk about in the book. 478 00:27:42,550 --> 00:27:47,115 So first of all, if you look at these hemispheres 479 00:27:47,115 --> 00:27:53,010 of a rodent, a cat, or a dog-- this is a cat-- and a human, 480 00:27:53,010 --> 00:27:57,080 what is the rhinal sulcus? 481 00:27:57,080 --> 00:27:59,260 In a rodent it's the one sulcus you 482 00:27:59,260 --> 00:28:01,790 can see from the lateral side. 483 00:28:01,790 --> 00:28:03,720 That sulcus. 484 00:28:03,720 --> 00:28:08,180 It simply separates the neocortex on one side 485 00:28:08,180 --> 00:28:10,470 from the olfactory cortex on the area. 486 00:28:10,470 --> 00:28:13,250 Two areas that have very different inputs 487 00:28:13,250 --> 00:28:15,350 and different functions. 488 00:28:15,350 --> 00:28:17,700 You see it in the cat here as well. 489 00:28:17,700 --> 00:28:22,260 You can follow it even in to the temporal lobe. 490 00:28:22,260 --> 00:28:24,214 In the human, it's there all right, 491 00:28:24,214 --> 00:28:25,880 but you don't see it in the lateral view 492 00:28:25,880 --> 00:28:32,570 because you would have to look from underneath to see it. 493 00:28:32,570 --> 00:28:37,480 And in these simplified drawings here of the hemisphere, 494 00:28:37,480 --> 00:28:39,420 look at the lower one here. 495 00:28:39,420 --> 00:28:41,470 There's the rhinal sulcus. 496 00:28:41,470 --> 00:28:43,900 There is one other sulcus, but it's on the medial side. 497 00:28:43,900 --> 00:28:49,290 It's the hippocampal where the infolding of the hippocampus 498 00:28:49,290 --> 00:28:50,710 forms a little sulcus there. 499 00:28:53,370 --> 00:28:56,690 I'm trying it here sort of the very rostral hippocampus 500 00:28:56,690 --> 00:28:58,475 in an animal like an opossum. 501 00:29:03,400 --> 00:29:07,110 Other mammals have it there too, but it's much tinier. 502 00:29:07,110 --> 00:29:10,220 It's only large caudally. 503 00:29:10,220 --> 00:29:11,830 What does this name mean? 504 00:29:11,830 --> 00:29:14,640 Olfactory peduncle. 505 00:29:14,640 --> 00:29:17,174 You go to medical school and these terms come up 506 00:29:17,174 --> 00:29:19,090 and you'll say, well, why didn't I learn that? 507 00:29:19,090 --> 00:29:20,170 Well, look. 508 00:29:20,170 --> 00:29:22,440 Here's the ventral view of the human brain. 509 00:29:22,440 --> 00:29:25,142 And this is the olfactory bulb. 510 00:29:25,142 --> 00:29:30,510 And then the darker orange there is the actual bulb. 511 00:29:30,510 --> 00:29:34,070 But if you insert a spatula under it--and we did this 512 00:29:34,070 --> 00:29:36,851 for the sheep, too-- you can actually lift that whole thing 513 00:29:36,851 --> 00:29:37,350 out. 514 00:29:37,350 --> 00:29:39,860 It's not just the bulb you're lifting out. 515 00:29:39,860 --> 00:29:44,020 It's the connections to the olfactory cortex. 516 00:29:44,020 --> 00:29:46,270 In fact, there's a little bit of olfactory cortex 517 00:29:46,270 --> 00:29:48,940 right in the peduncle. 518 00:29:48,940 --> 00:29:51,900 This all lifts up about back to here. 519 00:29:51,900 --> 00:29:53,440 And then the axons continue caudally 520 00:29:53,440 --> 00:29:57,080 and they go here and to the olfactory tubercle 521 00:29:57,080 --> 00:29:59,186 in the case of the forebrain and then 522 00:29:59,186 --> 00:30:01,270 to the various parts of the olfactory cortex. 523 00:30:01,270 --> 00:30:03,680 You can look back at the olfactory system chapters ans 524 00:30:03,680 --> 00:30:06,480 see these pictures. 525 00:30:06,480 --> 00:30:10,990 So that's what the olfactory tubercle is. 526 00:30:10,990 --> 00:30:13,090 And many animals have it. 527 00:30:13,090 --> 00:30:14,800 Many fish have the olfactory bulb. 528 00:30:14,800 --> 00:30:17,300 It's way, way out in the snout, and the brain's 529 00:30:17,300 --> 00:30:18,480 much further back. 530 00:30:18,480 --> 00:30:23,014 So you have the peduncle connecting the bulb 531 00:30:23,014 --> 00:30:24,055 to the rest of the brain. 532 00:30:24,055 --> 00:30:25,190 It's mostly axons. 533 00:30:30,390 --> 00:30:35,060 So we know that those axons of the peduncle 534 00:30:35,060 --> 00:30:36,830 are going to olfactory cortex. 535 00:30:36,830 --> 00:30:38,965 But they also-- olfactory information 536 00:30:38,965 --> 00:30:41,220 does reach the neocortex. 537 00:30:41,220 --> 00:30:42,400 How does it get there? 538 00:30:45,190 --> 00:30:46,860 It doesn't go directly. 539 00:30:46,860 --> 00:30:49,010 That's the first answer. 540 00:30:49,010 --> 00:30:53,370 It doesn't go from olfactory bulb to any area of neocortex. 541 00:30:53,370 --> 00:30:59,090 It goes to olfactory cortex and closely related structures 542 00:30:59,090 --> 00:31:02,300 like the amygdala and the olfactory tubercle. 543 00:31:06,670 --> 00:31:08,670 And there's several parts to the amygdala that's 544 00:31:08,670 --> 00:31:10,260 got such direct projections. 545 00:31:10,260 --> 00:31:15,700 We're not actually sure about the amygdala projections 546 00:31:15,700 --> 00:31:17,030 in humans. 547 00:31:17,030 --> 00:31:19,420 But it appears that it's similar human. 548 00:31:19,420 --> 00:31:24,320 And hamer has a nice picture of that. 549 00:31:24,320 --> 00:31:27,216 Then I based the picture in Chapter 19, 550 00:31:27,216 --> 00:31:28,840 picture of human olfactory projections, 551 00:31:28,840 --> 00:31:32,610 on the Hamer summary of that work. 552 00:31:35,810 --> 00:31:37,810 So how it does then it get to neocortex? 553 00:31:41,030 --> 00:31:44,190 It gets there mainly by way of the thalamus, 554 00:31:44,190 --> 00:31:50,050 just like all the other sensory pathways do. 555 00:31:50,050 --> 00:31:53,530 Most of the sensory information goes 556 00:31:53,530 --> 00:31:55,680 through the thalamic relay. 557 00:31:55,680 --> 00:32:00,850 So what is the olfactory nucleus of the thalamus? 558 00:32:00,850 --> 00:32:05,680 Well, there's the medial part of the medial dorsal nucleus which 559 00:32:05,680 --> 00:32:08,720 projects to the orbitofrontal context. 560 00:32:08,720 --> 00:32:12,920 You can consider it sort of the limbic part of the thalamus. 561 00:32:12,920 --> 00:32:14,770 Carries limbic system information 562 00:32:14,770 --> 00:32:16,985 to the orbitofrontal cortex. 563 00:32:16,985 --> 00:32:22,200 And that does get information from olfactory cortex, as well 564 00:32:22,200 --> 00:32:25,650 as other areas. 565 00:32:25,650 --> 00:32:28,640 Like it gets input from the hypothalamus as well, 566 00:32:28,640 --> 00:32:31,910 and from the amygdala. 567 00:32:31,910 --> 00:32:34,727 But there are other pathways. 568 00:32:34,727 --> 00:32:36,810 I probably should have mentioned them in the book, 569 00:32:36,810 --> 00:32:40,340 but they're not as prominent. 570 00:32:40,340 --> 00:32:43,590 Most of these areas go through the medial dorsal nucleus 571 00:32:43,590 --> 00:32:45,990 to get to the orbitofrontal cortex, 572 00:32:45,990 --> 00:32:48,880 but the amygdala itself gets olfactory input 573 00:32:48,880 --> 00:32:54,840 and the amygdala has projections to the prefrontal cortex 574 00:32:54,840 --> 00:32:56,430 as well. 575 00:32:56,430 --> 00:32:58,310 And those parts that get olfactory inputs 576 00:32:58,310 --> 00:33:01,860 have projections to the orbitofrontal. 577 00:33:01,860 --> 00:33:05,770 And then there are some basal forebrain projections 578 00:33:05,770 --> 00:33:10,070 that are getting olfactory input that have some projections that 579 00:33:10,070 --> 00:33:11,820 reach that same area. 580 00:33:17,980 --> 00:33:23,270 So let's just summarize now these major thalamalcortical 581 00:33:23,270 --> 00:33:24,720 projections. 582 00:33:24,720 --> 00:33:29,800 Here's a verbal description of the major areas of thalamus-- 583 00:33:29,800 --> 00:33:31,810 the geniculate bodies, the lateral thalamus, 584 00:33:31,810 --> 00:33:35,420 the ventral thalamus, both the somatosensory part 585 00:33:35,420 --> 00:33:39,780 and the motor part, and then the medidorsal nucleus, 586 00:33:39,780 --> 00:33:43,730 the anterior nuclei, and finally the older parts 587 00:33:43,730 --> 00:33:46,060 of the thalamus, the intralaminar and midline. 588 00:33:46,060 --> 00:33:48,870 And these are the pictures I used. 589 00:33:48,870 --> 00:33:52,870 So I've used a color code here and I've 590 00:33:52,870 --> 00:33:55,860 outlined in different colors the major regions. 591 00:33:55,860 --> 00:33:59,230 So what is in blue here? 592 00:33:59,230 --> 00:34:03,760 The areas that project to what we call central cortex. 593 00:34:03,760 --> 00:34:07,600 Central means somatosensory, motor, and premotor. 594 00:34:07,600 --> 00:34:11,699 Or just sensory and somatosensory and somatomotor. 595 00:34:14,890 --> 00:34:20,170 And probably also somatosensory to begin with, originally. 596 00:34:20,170 --> 00:34:22,150 So these are the central areas. 597 00:34:22,150 --> 00:34:25,690 They're the areas that give rise to the longest axons 598 00:34:25,690 --> 00:34:31,139 that we've talked about earlier, many of which 599 00:34:31,139 --> 00:34:34,739 go to the spinal cord from all of these areas. 600 00:34:34,739 --> 00:34:37,440 So I show in the darkest color there 601 00:34:37,440 --> 00:34:41,969 the primary somatosensory areas; Brodmann's areas 3, 1, and 2; 602 00:34:41,969 --> 00:34:44,646 and this would be area 4 and this 603 00:34:44,646 --> 00:34:47,389 would be area 6, the premotor cortex. 604 00:34:47,389 --> 00:34:51,440 Those get their inputs primarily from these cell groups 605 00:34:51,440 --> 00:34:53,534 in the thalamus of the ventral nucleus. 606 00:34:56,360 --> 00:34:58,710 It's hard to see the way I've drawn it here, 607 00:34:58,710 --> 00:35:00,990 that these are all more ventral. 608 00:35:00,990 --> 00:35:03,440 Actually, the VA does get quite dorsal 609 00:35:03,440 --> 00:35:06,220 when go-- that's in the more anterior thalamus. 610 00:35:06,220 --> 00:35:10,220 It reaches dorsal surface right next to the anterior nuclei. 611 00:35:13,370 --> 00:35:17,140 So the ventral basal, the most caudal and most ventral 612 00:35:17,140 --> 00:35:21,460 part of that goes-- that group of nuclei 613 00:35:21,460 --> 00:35:23,360 is getting the direct somatosensory 614 00:35:23,360 --> 00:35:28,080 input from spinalthalamic tract and the lemniscus and so forth. 615 00:35:28,080 --> 00:35:30,990 These are the ones that go to motor cortex. 616 00:35:30,990 --> 00:35:33,190 Primary motor mainly from VL, which 617 00:35:33,190 --> 00:35:35,440 is getting heavy inputs from the cerebellum. 618 00:35:39,870 --> 00:35:46,060 Some from the corpus striatum, the globus pallidus. 619 00:35:46,060 --> 00:35:50,750 And then the VA, which gets heavy input 620 00:35:50,750 --> 00:35:56,170 from the globus pallidus, the striatal outputs. 621 00:35:56,170 --> 00:35:58,030 And that's going to the premotor area. 622 00:36:01,960 --> 00:36:04,530 And remember the difference in function between these two 623 00:36:04,530 --> 00:36:05,300 areas. 624 00:36:05,300 --> 00:36:09,250 Premotor areas stays more involved in actual behavior 625 00:36:09,250 --> 00:36:11,440 because they always get patterns in behavior 626 00:36:11,440 --> 00:36:13,130 when they simulate there. 627 00:36:13,130 --> 00:36:14,870 So simulate the motor cortex, you're 628 00:36:14,870 --> 00:36:21,210 getting individual components, single digits, single muscle 629 00:36:21,210 --> 00:36:22,970 groups. 630 00:36:22,970 --> 00:36:26,100 There's been a lot of argument about what exactly-- 631 00:36:26,100 --> 00:36:27,360 what's represented here. 632 00:36:27,360 --> 00:36:30,821 But it's always a small piece of the body. 633 00:36:34,200 --> 00:36:40,080 Anterior nuclei are going to that cortex 634 00:36:40,080 --> 00:36:43,615 just above, in front, and behind the corpus callosum. 635 00:36:43,615 --> 00:36:45,920 The cingulate cortex and the retrosplenial cortex. 636 00:36:49,340 --> 00:36:51,510 And that I've outlined in the pink there. 637 00:36:54,950 --> 00:36:56,490 So now let's what's left? 638 00:36:56,490 --> 00:36:59,230 Start with the geniculate bodies. 639 00:36:59,230 --> 00:37:01,290 Lateral and medial geniculate bodies, 640 00:37:01,290 --> 00:37:03,245 primary visual and primary auditory areas. 641 00:37:06,170 --> 00:37:08,360 And depending on how much you include 642 00:37:08,360 --> 00:37:10,140 in the medial geniculate, you would 643 00:37:10,140 --> 00:37:13,510 include some of the areas around the primary auditory cortex 644 00:37:13,510 --> 00:37:14,010 there. 645 00:37:16,680 --> 00:37:19,420 And then what's left? 646 00:37:19,420 --> 00:37:21,850 Other than the intralaminar which I don't show here 647 00:37:21,850 --> 00:37:25,620 which project quite widely to the cortex. 648 00:37:25,620 --> 00:37:27,720 You two major structures. 649 00:37:27,720 --> 00:37:31,180 The MD, the medial dorsal nucleus, 650 00:37:31,180 --> 00:37:35,870 and the lateral thalamus, which has several components. 651 00:37:35,870 --> 00:37:40,616 But some people call-- in primates-- call the whole thing 652 00:37:40,616 --> 00:37:44,790 the pulvinar, except, perhaps, for the anterior areas. 653 00:37:44,790 --> 00:37:47,180 Other people like to keep the LP, 654 00:37:47,180 --> 00:37:51,120 LV be here, LP, and pulvinar separate. 655 00:37:51,120 --> 00:37:53,910 But it's all lateral thalamus, so I grouped it all together 656 00:37:53,910 --> 00:37:55,960 and I've shown that that projects 657 00:37:55,960 --> 00:37:59,760 to this entire huge expanse in primates. 658 00:37:59,760 --> 00:38:05,580 Not so big in other animals, like the rodent. 659 00:38:05,580 --> 00:38:08,500 The posterior association cortex, 660 00:38:08,500 --> 00:38:12,720 both unimodal and multimodal or heteromodal. 661 00:38:16,190 --> 00:38:20,210 And the MD, same kinds of projections 662 00:38:20,210 --> 00:38:22,020 but now they hit prefrontal areas, 663 00:38:22,020 --> 00:38:24,780 the areas in front of the motor areas. 664 00:38:27,310 --> 00:38:31,540 And I do show here-- you see that I've mixed here 665 00:38:31,540 --> 00:38:35,810 with the model pink for the MD projections. 666 00:38:35,810 --> 00:38:38,010 I mixed some orange. 667 00:38:38,010 --> 00:38:40,280 You see it ventrally here. 668 00:38:40,280 --> 00:38:41,630 You see it here. 669 00:38:41,630 --> 00:38:43,880 And then I've mixed some of the model pink 670 00:38:43,880 --> 00:38:47,300 there with-- in the temporal pole. 671 00:38:47,300 --> 00:38:50,370 That's, quite simply, because these areas-- 672 00:38:50,370 --> 00:38:52,830 to the medial part of the mediodorsal 673 00:38:52,830 --> 00:38:57,090 and the medial part of the pulvinar-- 674 00:38:57,090 --> 00:39:01,270 do have overlapping projections to both these areas. 675 00:39:01,270 --> 00:39:04,630 In fact, it's continuous into parts of the cingulate 676 00:39:04,630 --> 00:39:05,590 here as well. 677 00:39:08,320 --> 00:39:13,290 So those are the major territories. 678 00:39:13,290 --> 00:39:15,770 Obviously there's many different regions 679 00:39:15,770 --> 00:39:19,490 that get input from various parts of the lateral thalamus. 680 00:39:19,490 --> 00:39:24,157 Same is true for the mediodorsal nucleus. 681 00:39:24,157 --> 00:39:28,370 Now of you take a section from an embryonic human, 682 00:39:28,370 --> 00:39:32,680 it looks just like a rat or a hamster or a mouse. 683 00:39:32,680 --> 00:39:35,900 There's the geniculate body. 684 00:39:35,900 --> 00:39:40,660 That's where the-- you could call it lateral posterior 685 00:39:40,660 --> 00:39:43,100 nucleus in a rodent-- but that's what 686 00:39:43,100 --> 00:39:48,000 will become the pulvinar as the human goes up. 687 00:39:48,000 --> 00:39:50,530 This is an embryonic human. 688 00:39:50,530 --> 00:39:53,330 This is a picture of a cross-section 689 00:39:53,330 --> 00:39:55,320 of the very caudal pulvinar. 690 00:39:55,320 --> 00:39:58,750 So you would make a section here and this 691 00:39:58,750 --> 00:40:00,350 would be a transverse section. 692 00:40:00,350 --> 00:40:05,680 It would go right through the two geniculate bodies 693 00:40:05,680 --> 00:40:08,440 and through the caudal into the pulvinar, 694 00:40:08,440 --> 00:40:10,300 and that's what you're seeing here. 695 00:40:10,300 --> 00:40:12,620 This isn't even the biggest part of the pulvinar. 696 00:40:12,620 --> 00:40:14,610 But you see it's grown so much it's 697 00:40:14,610 --> 00:40:16,780 pushed the geniculate body over. 698 00:40:16,780 --> 00:40:20,860 So you have that horseshoe shape. 699 00:40:20,860 --> 00:40:24,507 The medial geniculate is now medial 700 00:40:24,507 --> 00:40:25,590 to the lateral geniculate. 701 00:40:30,250 --> 00:40:34,050 And here's the rodent, where I've used the same color scheme 702 00:40:34,050 --> 00:40:36,390 to indicate the same kinds of things. 703 00:40:36,390 --> 00:40:40,170 You'll note here that the premotor and the prefrontal 704 00:40:40,170 --> 00:40:44,280 are not as sharply distinguishable, 705 00:40:44,280 --> 00:40:49,380 though they-- by projections you can indicate 706 00:40:49,380 --> 00:40:51,690 where the main prefrontal nucleus is just 707 00:40:51,690 --> 00:40:53,744 by MD projections. 708 00:40:53,744 --> 00:40:55,160 It goes right to the frontal pole, 709 00:40:55,160 --> 00:40:59,400 and then on the medial side it covers this whole region. 710 00:40:59,400 --> 00:41:01,630 Colors maybe didn't show that too well, 711 00:41:01,630 --> 00:41:03,975 but it's-- also the rostral. 712 00:41:07,540 --> 00:41:09,950 This rostral cingulate area, and people 713 00:41:09,950 --> 00:41:11,630 vary in how they name those. 714 00:41:11,630 --> 00:41:14,440 It could just be called prefrontal cortex. 715 00:41:17,590 --> 00:41:20,552 And paraolfactory region down here. 716 00:41:20,552 --> 00:41:24,760 But anyway, those are the equivalent areas in a rodent. 717 00:41:24,760 --> 00:41:28,255 And you'll note that the size of the prefrontal areas 718 00:41:28,255 --> 00:41:33,750 and the size of the posterior associations 719 00:41:33,750 --> 00:41:38,840 are nowhere near the size in large primates, especially 720 00:41:38,840 --> 00:41:41,810 in humans. 721 00:41:41,810 --> 00:41:46,390 So Nauta used to say that the association areas are what's 722 00:41:46,390 --> 00:41:49,740 left when you specify the sensory functions 723 00:41:49,740 --> 00:41:53,470 of the [INAUDIBLE] of the neocortex. 724 00:41:53,470 --> 00:41:56,810 But we've learned a lot since that time 725 00:41:56,810 --> 00:41:58,160 by functional studies. 726 00:41:58,160 --> 00:42:02,860 Now we've expanded the size of the-- it's 727 00:42:02,860 --> 00:42:07,310 been quite surprising how many unimodal visual areas there 728 00:42:07,310 --> 00:42:09,320 are. 729 00:42:09,320 --> 00:42:13,790 They include a lot of this cortex. 730 00:42:13,790 --> 00:42:19,300 So let's just show that here. 731 00:42:19,300 --> 00:42:22,720 The best definition now of association areas 732 00:42:22,720 --> 00:42:24,030 is in terms of the anatomy. 733 00:42:26,760 --> 00:42:28,815 Many psychologists use to think, oh, 734 00:42:28,815 --> 00:42:32,850 that should be for-- that's where we form associations, 735 00:42:32,850 --> 00:42:37,120 between different modalities and between sensory and motor. 736 00:42:37,120 --> 00:42:39,020 But in fact, it's defined anatomically 737 00:42:39,020 --> 00:42:42,440 by the long transcortical connections. 738 00:42:42,440 --> 00:42:46,360 It is the multimodal areas that have the longest connection. 739 00:42:46,360 --> 00:42:48,660 You can see a lot of them in a brain dissection. 740 00:42:48,660 --> 00:42:55,530 This another picture of the major fiber 741 00:42:55,530 --> 00:42:58,240 bundles that you can make out in a dissection. 742 00:42:58,240 --> 00:43:01,880 And they were given names just on the basis of the dissection. 743 00:43:01,880 --> 00:43:05,725 This unciante transmitted or the hook-shaped bundle 744 00:43:05,725 --> 00:43:10,930 from anterior temporal to the orbital prefrontal. 745 00:43:10,930 --> 00:43:13,390 And then the arcuate, these fibers 746 00:43:13,390 --> 00:43:16,460 that arc around from the posterior 747 00:43:16,460 --> 00:43:19,070 parts of the temporal lobe all the way into frontal lobe. 748 00:43:21,690 --> 00:43:25,270 And then long longitudinal bundles, 749 00:43:25,270 --> 00:43:28,600 superior longitudinal fasiculus, superior occipitofrontal 750 00:43:28,600 --> 00:43:29,862 fasiculus. 751 00:43:29,862 --> 00:43:31,653 Now, these have been traced experimentally. 752 00:43:34,230 --> 00:43:36,780 Not in humans, of course, although there 753 00:43:36,780 --> 00:43:40,390 are better and better methods for seeing these now in humans. 754 00:43:40,390 --> 00:43:43,090 But this is a summary that I made up 755 00:43:43,090 --> 00:43:45,800 from the various studies that Deepak 756 00:43:45,800 --> 00:43:50,590 Pandya and his associates had found. 757 00:43:50,590 --> 00:43:55,910 And Kathy Rockland, who has been working with the Tonegawa 758 00:43:55,910 --> 00:44:02,110 group for a while, participated in some of these studies. 759 00:44:02,110 --> 00:44:07,855 But this just shows these major transcortical fiber bundles. 760 00:44:07,855 --> 00:44:11,380 They're coming from those association areas, primarily 761 00:44:11,380 --> 00:44:17,340 the multimodal areas, but also unimodal, here 762 00:44:17,340 --> 00:44:19,930 especially for the visual system. 763 00:44:19,930 --> 00:44:23,820 You see these many long fiber bundles. 764 00:44:23,820 --> 00:44:27,860 So then I just said, how can you verify 765 00:44:27,860 --> 00:44:32,030 these for the human brain other than the use of postmortem 766 00:44:32,030 --> 00:44:34,490 dissection? 767 00:44:34,490 --> 00:44:35,710 What is the method called? 768 00:44:40,090 --> 00:44:42,040 It uses diffusion of water molecules 769 00:44:42,040 --> 00:44:44,050 in a primary direction. 770 00:44:44,050 --> 00:44:48,010 So diffusion tensor imaging is a common name for it. 771 00:44:48,010 --> 00:44:50,450 It has a couple of other terms that are used 772 00:44:50,450 --> 00:44:53,029 and you will find if you just search under diffusion tensor 773 00:44:53,029 --> 00:44:54,820 imaging, you'll find many of these studies. 774 00:44:57,800 --> 00:45:00,950 I asked some of the limitations of the method. 775 00:45:00,950 --> 00:45:02,910 Main one is resolution. 776 00:45:02,910 --> 00:45:08,070 You can't-- you're never anywhere near the level 777 00:45:08,070 --> 00:45:13,070 of cells as you are when you do experimental tracing work. 778 00:45:13,070 --> 00:45:16,950 And another limitation is it depends on the computer 779 00:45:16,950 --> 00:45:19,710 algorithm that you're using to do the tracing. 780 00:45:19,710 --> 00:45:22,700 So the picture I put in the book, if you look carefully, 781 00:45:22,700 --> 00:45:25,140 I believe it shows fibers going from cortex up 782 00:45:25,140 --> 00:45:27,220 into the cerebellum. 783 00:45:27,220 --> 00:45:30,800 Do any fibers do that in any of the experimental studies? 784 00:45:30,800 --> 00:45:31,760 No. 785 00:45:31,760 --> 00:45:34,260 But they cross, they come right next 786 00:45:34,260 --> 00:45:39,280 to fibers of the pontocerebellar projection. 787 00:45:39,280 --> 00:45:42,180 So depending on how your algorithm is set, 788 00:45:42,180 --> 00:45:46,780 you might get some of these fibers. 789 00:45:46,780 --> 00:45:51,170 You would cross from one major bundle to another. 790 00:45:51,170 --> 00:45:55,000 So it's very dependent on the math 791 00:45:55,000 --> 00:45:59,005 and on the computational methods you're using. 792 00:45:59,005 --> 00:46:01,820 But people are-- they're getting better and better at it. 793 00:46:01,820 --> 00:46:04,230 But you always have that limitation of resolution. 794 00:46:08,010 --> 00:46:10,781 This just shows some of the diffusion tensor imaging 795 00:46:10,781 --> 00:46:11,280 picture. 796 00:46:11,280 --> 00:46:13,570 I think I put this one in the book. 797 00:46:13,570 --> 00:46:17,510 It was interesting because it showed a developmental change 798 00:46:17,510 --> 00:46:20,140 in fibers that come into the Broca's 799 00:46:20,140 --> 00:46:22,375 region of the frontal lobe, areas we know 800 00:46:22,375 --> 00:46:24,610 are important for speaking. 801 00:46:24,610 --> 00:46:30,840 And you see in the newborn, they showed two major routes. 802 00:46:30,840 --> 00:46:33,390 A third route appeared later. 803 00:46:33,390 --> 00:46:37,990 So in the adults, you see three major groups of fibers. 804 00:46:37,990 --> 00:46:42,640 You only see two in the babies. 805 00:46:42,640 --> 00:46:44,120 So that's the kind of information 806 00:46:44,120 --> 00:46:50,700 that we didn't have just on basis of dissections these-- 807 00:46:50,700 --> 00:46:53,329 to study things related to Broca's area. 808 00:46:53,329 --> 00:46:54,995 Of course, you have to use human brains. 809 00:46:58,840 --> 00:47:03,252 I want you to understand those Mesulam types 810 00:47:03,252 --> 00:47:05,785 which we mentioned briefly earlier. 811 00:47:08,590 --> 00:47:10,530 And you should know what the association 812 00:47:10,530 --> 00:47:12,140 layers of mediocortex are. 813 00:47:12,140 --> 00:47:13,570 You can guess what they are. 814 00:47:13,570 --> 00:47:15,910 When we talk about association layers, 815 00:47:15,910 --> 00:47:19,496 which layers give rise to-- the main layers that give rise 816 00:47:19,496 --> 00:47:24,050 to transcortical projections and callosal fibers too? 817 00:47:24,050 --> 00:47:29,320 Layers 2 and 3 above-- remember, when neocortex appeared, 818 00:47:29,320 --> 00:47:30,610 these new layers appeared. 819 00:47:30,610 --> 00:47:33,740 They were superficial layers, layers 2, 3, and 4. 820 00:47:36,740 --> 00:47:40,890 The older cortex, the dorsal cortex of non-mammals, 821 00:47:40,890 --> 00:47:43,570 they had the equivalent of the deeper two layers. 822 00:47:46,990 --> 00:47:49,720 The association layer, the association fibers, 823 00:47:49,720 --> 00:47:54,430 transcortical, come from those superficial layers 2 and 3. 824 00:47:54,430 --> 00:47:56,200 So there have been some special studies 825 00:47:56,200 --> 00:47:58,680 now of those two layers. 826 00:47:58,680 --> 00:48:02,465 And first of all, I just summarized for you 827 00:48:02,465 --> 00:48:04,490 the Mesulam types. 828 00:48:04,490 --> 00:48:06,610 I show you this picture, which doesn't 829 00:48:06,610 --> 00:48:09,282 show the transcorticals. 830 00:48:09,282 --> 00:48:13,720 If you look here under higher order heteromodal association 831 00:48:13,720 --> 00:48:16,840 areas, what it's not showing is that these areas 832 00:48:16,840 --> 00:48:18,526 interconnect with each other. 833 00:48:18,526 --> 00:48:22,030 The posterior association areas interconnect 834 00:48:22,030 --> 00:48:25,720 the anterior association areas. 835 00:48:25,720 --> 00:48:30,490 I'm just showing the connections between these areas 836 00:48:30,490 --> 00:48:34,990 and the adjoining unimodal areas and the, 837 00:48:34,990 --> 00:48:37,800 on the other side, the paralimbic areas. 838 00:48:37,800 --> 00:48:40,430 The major route to paralimbic areas 839 00:48:40,430 --> 00:48:43,606 is from those multimodal association areas. 840 00:48:46,930 --> 00:48:52,720 And this is a very useful picture of Mesulam. 841 00:48:52,720 --> 00:48:54,860 A beautiful color picture that I use 842 00:48:54,860 --> 00:48:59,640 the base the functional picture that I drew up 843 00:48:59,640 --> 00:49:04,530 for the book showing these major types of functions-- sensory 844 00:49:04,530 --> 00:49:09,490 and perceptual, motor, behavior-- meaning pattern 845 00:49:09,490 --> 00:49:14,360 movements-- and then motivation. 846 00:49:14,360 --> 00:49:22,950 And it's based on the Mesulam depiction of the various types 847 00:49:22,950 --> 00:49:27,620 of cortex he shows in this box diagram. 848 00:49:27,620 --> 00:49:29,550 And if you blow it up, you'll see 849 00:49:29,550 --> 00:49:32,390 the see the Brodmann numbers listed. 850 00:49:32,390 --> 00:49:38,260 He's used-- what do his letters mean? 851 00:49:38,260 --> 00:49:42,590 This is M1. 852 00:49:42,590 --> 00:49:43,890 What does MA mean? 853 00:49:43,890 --> 00:49:47,090 It means motor association. 854 00:49:47,090 --> 00:49:51,800 That's what he calls the premotor areas. 855 00:49:51,800 --> 00:49:53,470 So it's unimodal. 856 00:49:53,470 --> 00:49:54,950 Still motor. 857 00:49:54,950 --> 00:50:01,280 But it's getting many connections from its primary. 858 00:50:01,280 --> 00:50:04,280 He doesn't mean it doesn't get any thalamic input. 859 00:50:04,280 --> 00:50:05,260 It does. 860 00:50:05,260 --> 00:50:08,340 But it also gets a lot more transcortical input. 861 00:50:08,340 --> 00:50:14,420 And then prefrontal cortex we see. 862 00:50:14,420 --> 00:50:18,930 So similarly here, the unimodal association provision. 863 00:50:18,930 --> 00:50:23,410 But look at the two heteromodal areas. 864 00:50:23,410 --> 00:50:27,550 I've left those areas-- the multimodal areas-- white here. 865 00:50:27,550 --> 00:50:30,282 So I talk about what are the two heteromodal fields 866 00:50:30,282 --> 00:50:33,030 or multimodal fields in the primate brain? 867 00:50:33,030 --> 00:50:34,300 Which is larger? 868 00:50:34,300 --> 00:50:37,160 And what are the thalamic nuclei that connect with them? 869 00:50:37,160 --> 00:50:40,002 Well, you can see them right away here. 870 00:50:40,002 --> 00:50:43,430 The prefrontal area anteriorly. 871 00:50:43,430 --> 00:50:47,680 And posteriorly, it's posterior, parietal, and temporal. 872 00:50:47,680 --> 00:50:51,220 And much of it is buried in the sulcus here. 873 00:50:51,220 --> 00:50:54,300 Those are where the main multimodal areas are. 874 00:50:54,300 --> 00:50:56,570 And it looks like prefrontal is bigger, 875 00:50:56,570 --> 00:50:58,140 though there has been argument. 876 00:50:58,140 --> 00:51:03,320 And one reason is that the primarily unimodal visual areas 877 00:51:03,320 --> 00:51:06,220 occupy so much of the association cortex posteriorly. 878 00:51:09,740 --> 00:51:14,700 Here you see them from the medial side. 879 00:51:14,700 --> 00:51:17,340 And what are the thalamic nuclei? 880 00:51:17,340 --> 00:51:21,490 Well, the lateral nuclei and the medial dorsal nucleus. 881 00:51:21,490 --> 00:51:27,700 Here it is in a rodent and here it is in an embryonic human 882 00:51:27,700 --> 00:51:31,625 and in an adult human where you just see the pulvinar there. 883 00:51:31,625 --> 00:51:34,860 Maybe a dorsal would still look similar. 884 00:51:34,860 --> 00:51:38,290 And there you see the colors showing 885 00:51:38,290 --> 00:51:43,610 the relative size in rodent and then in human. 886 00:51:43,610 --> 00:51:47,450 And I won't spend time on Mesulam's different way 887 00:51:47,450 --> 00:51:50,260 of dividing up major divisions of cortex. 888 00:51:50,260 --> 00:51:52,740 It's rather interesting, but much more difficult 889 00:51:52,740 --> 00:51:57,495 to get your head around. 890 00:51:57,495 --> 00:52:00,090 And this is the one would be more 891 00:52:00,090 --> 00:52:02,880 useful to anyway in the future. 892 00:52:02,880 --> 00:52:06,700 So what we will do next time, I'll 893 00:52:06,700 --> 00:52:13,110 say a little bit about Poliakoff and the study he presented done 894 00:52:13,110 --> 00:52:16,110 in Moscow of the association layers 895 00:52:16,110 --> 00:52:20,240 and the work done in the West that relates to it. 896 00:52:20,240 --> 00:52:23,860 The most interesting fact there is that in those association 897 00:52:23,860 --> 00:52:26,260 layers, layers 2 and 3, are where, 898 00:52:26,260 --> 00:52:28,115 when you look at individual cells 899 00:52:28,115 --> 00:52:30,990 and hold them in imaging over a long enough time, 900 00:52:30,990 --> 00:52:35,220 you see the cells are changing. 901 00:52:35,220 --> 00:52:36,320 They're plastic. 902 00:52:36,320 --> 00:52:39,820 The GABAergic interneurons appear 903 00:52:39,820 --> 00:52:43,410 to be the plastic cells of the cortex. 904 00:52:43,410 --> 00:52:45,180 And that probably holds true throughout 905 00:52:45,180 --> 00:52:47,200 the entire cortical mantle. 906 00:52:47,200 --> 00:52:49,940 And more and more physiology studies are supporting that, 907 00:52:49,940 --> 00:52:55,320 but we had data from morphology even before the studies I just 908 00:52:55,320 --> 00:52:58,845 mentioned, which were done here at MIT by Elly Nedivi working 909 00:52:58,845 --> 00:53:01,950 with engineers. 910 00:53:01,950 --> 00:53:05,360 We knew that that's where the growth associated protein 911 00:53:05,360 --> 00:53:06,490 remained. 912 00:53:06,490 --> 00:53:09,180 It's always present in developing axons, 913 00:53:09,180 --> 00:53:12,835 but it remains in the cortex primarily in those association 914 00:53:12,835 --> 00:53:18,680 layers, and also in association areas of the thalamus. 915 00:53:18,680 --> 00:53:20,690 I was involved in only a few of those studies 916 00:53:20,690 --> 00:53:21,860 with Larry Benowtiz. 917 00:53:21,860 --> 00:53:25,390 He did most of it. 918 00:53:25,390 --> 00:53:30,450 Rachel Neve, who's working upstairs on the sixth floor, 919 00:53:30,450 --> 00:53:33,180 was also involved in those studies. 920 00:53:33,180 --> 00:53:34,063 All right. 921 00:53:34,063 --> 00:53:38,610 So we'll come back to that and say a little more 922 00:53:38,610 --> 00:53:41,690 about neocortex in the last lecture.