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 00:00:23,390 --> 00:00:25,560 PROFESSOR: Let's finish this discussion 9 00:00:25,560 --> 00:00:29,990 of the spatial organization of the motor, the descending 10 00:00:29,990 --> 00:00:31,595 pathways of motor system. 11 00:00:35,060 --> 00:00:38,900 We had talked about these pathways 12 00:00:38,900 --> 00:00:42,065 shown in these diagrams, and gone over them a little bit. 13 00:00:48,140 --> 00:00:56,160 I just mentioned the bilateral lesions of the medial pathways. 14 00:00:56,160 --> 00:00:57,350 They had to be bilateral. 15 00:00:57,350 --> 00:01:00,660 Because those pathways tend to distribute on both sides. 16 00:01:00,660 --> 00:01:05,680 So the only way to really eliminate 17 00:01:05,680 --> 00:01:10,160 the medial pathways in a way that would really 18 00:01:10,160 --> 00:01:12,710 impact function, is to get rid of them on both sides. 19 00:01:12,710 --> 00:01:15,880 And they really can't control their body acts well at all. 20 00:01:15,880 --> 00:01:17,710 So they can't write. 21 00:01:17,710 --> 00:01:21,200 They can't walk straight. 22 00:01:21,200 --> 00:01:24,110 They can't even orient their heads very well. 23 00:01:24,110 --> 00:01:26,540 Because the tectum is pretty dominant. 24 00:01:26,540 --> 00:01:31,590 And after the cortex is removed, remember 25 00:01:31,590 --> 00:01:34,450 that was critical to these experiments. 26 00:01:34,450 --> 00:01:38,320 They had to remove the pyramidal tract first. 27 00:01:38,320 --> 00:01:39,850 Actually the cortex was intact. 28 00:01:39,850 --> 00:01:43,940 It's still connected to the brain stem, 29 00:01:43,940 --> 00:01:46,380 except the lower most brain stem. 30 00:01:46,380 --> 00:01:49,310 And that means they have normal eye movements. 31 00:01:49,310 --> 00:01:52,210 So you can tell that the monkey knows where he wants to walk. 32 00:01:52,210 --> 00:01:54,760 And yet he can't steer himself well, 33 00:01:54,760 --> 00:02:00,310 because he doesn't have good control of the axial muscles 34 00:02:00,310 --> 00:02:01,190 below his head. 35 00:02:07,450 --> 00:02:11,910 He does-- is able to control this hands though. 36 00:02:11,910 --> 00:02:13,360 The only way they could test that 37 00:02:13,360 --> 00:02:15,470 was to strap him in a chair so he doesn't 38 00:02:15,470 --> 00:02:18,390 have to struggle to try to balance. 39 00:02:18,390 --> 00:02:20,740 So then his arms are just dangling 40 00:02:20,740 --> 00:02:22,355 and they can present things to him, 41 00:02:22,355 --> 00:02:24,430 and he can be able to use his vision 42 00:02:24,430 --> 00:02:29,260 to guide his hand to grasp food objects. 43 00:02:29,260 --> 00:02:32,750 He does that pretty well. 44 00:02:32,750 --> 00:02:33,250 All right. 45 00:02:36,620 --> 00:02:40,160 And then the other lesion that is 46 00:02:40,160 --> 00:02:42,360 instead of cutting the medial pathways, 47 00:02:42,360 --> 00:02:44,800 they can go in and cut the lateral pathways just 48 00:02:44,800 --> 00:02:46,180 on one side. 49 00:02:46,180 --> 00:02:50,730 Because they don't tend to distribute bilaterally. 50 00:02:50,730 --> 00:02:53,140 And then they got very big differences 51 00:02:53,140 --> 00:02:55,970 in control of the two hands. 52 00:02:55,970 --> 00:03:01,330 So if they cut the pathways on the left side, 53 00:03:01,330 --> 00:03:04,910 he would reach in with his right hand and grasp things, 54 00:03:04,910 --> 00:03:08,710 not with single digits, but with using the whole hand. 55 00:03:08,710 --> 00:03:09,890 So he could grasp things. 56 00:03:09,890 --> 00:03:13,670 But with this hand he knows exactly what he wants to do. 57 00:03:13,670 --> 00:03:16,070 He would reach. 58 00:03:16,070 --> 00:03:18,152 The hand just wouldn't grasp. 59 00:03:18,152 --> 00:03:21,320 He has control of his arm muscles 60 00:03:21,320 --> 00:03:30,000 but he can't do that, so very selective types of paralysis. 61 00:03:30,000 --> 00:03:33,090 Now one of the most interesting parts of that lesion 62 00:03:33,090 --> 00:03:41,370 is that if they let the monkey go, so he can run and climb 63 00:03:41,370 --> 00:03:44,330 his cage and everything, while he's 64 00:03:44,330 --> 00:03:46,390 doing that he's got good control of the hands. 65 00:03:46,390 --> 00:03:49,160 So what's going on? 66 00:03:49,160 --> 00:03:53,840 When the whole body is involved that system for axial muscle 67 00:03:53,840 --> 00:03:57,005 control is really a whole body control system. 68 00:03:57,005 --> 00:04:01,090 It controls things like locomotion and climbing. 69 00:04:01,090 --> 00:04:05,365 And so in those movements he can control his grasping. 70 00:04:05,365 --> 00:04:09,450 But when you ask him to grasp as an individual movement, 71 00:04:09,450 --> 00:04:12,360 separate from other movements, then he can't do it. 72 00:04:15,482 --> 00:04:18,130 It's a good lesson on what paralysis 73 00:04:18,130 --> 00:04:21,290 means when it's due to a central lesion. 74 00:04:21,290 --> 00:04:24,740 If it's due to a lesion that affects the motor 75 00:04:24,740 --> 00:04:27,750 neurons or the axons from motor neurons, 76 00:04:27,750 --> 00:04:29,740 then you get a flaccid paralysis. 77 00:04:29,740 --> 00:04:31,490 The muscles are just totally relaxed. 78 00:04:31,490 --> 00:04:34,240 They're not getting their input anymore. 79 00:04:34,240 --> 00:04:36,940 We're just talking about central lesions here. 80 00:04:40,210 --> 00:04:43,740 So those experiments made clear two very different things. 81 00:04:43,740 --> 00:04:47,440 One is the spatial layout of the motor pathways, the descending 82 00:04:47,440 --> 00:04:49,190 pathways. 83 00:04:49,190 --> 00:04:53,060 And the other point was the quantitative dominance 84 00:04:53,060 --> 00:04:58,220 of the cortical pathways in monkeys and of course humans. 85 00:04:58,220 --> 00:05:01,000 All of those things described in monkeys, 86 00:05:01,000 --> 00:05:07,240 you can find clinical cases that match parts of them. 87 00:05:07,240 --> 00:05:09,120 But of course, the monkeys gave the advantage 88 00:05:09,120 --> 00:05:11,300 of being able to control the lesion much better. 89 00:05:16,720 --> 00:05:20,980 What's the major symptoms of you just cut all these pathways? 90 00:05:20,980 --> 00:05:24,640 You can do it-- say someone, a person or a monkey 91 00:05:24,640 --> 00:05:26,880 has a transected spinal cord. 92 00:05:26,880 --> 00:05:30,500 They die if the lesion is above C4. 93 00:05:30,500 --> 00:05:32,630 Why is that? 94 00:05:32,630 --> 00:05:35,270 They stop breathing. 95 00:05:35,270 --> 00:05:38,870 So you've got to have intact spinal cord down 96 00:05:38,870 --> 00:05:43,250 to the fourth cervical level to get control 97 00:05:43,250 --> 00:05:46,095 of the diaphragm for breathing. 98 00:05:52,000 --> 00:05:53,500 But what happens to them then? 99 00:05:53,500 --> 00:05:59,110 Say around C4 or C5 you get a spinal transection. 100 00:05:59,110 --> 00:06:01,200 Say there's an auto accident. 101 00:06:01,200 --> 00:06:03,500 The neck is broken. 102 00:06:03,500 --> 00:06:06,880 If his breathing survives, he will live. 103 00:06:06,880 --> 00:06:10,255 But he becomes what? 104 00:06:12,925 --> 00:06:15,250 What's the term? 105 00:06:15,250 --> 00:06:19,110 Quadriplegic or the actual grammatically correct word 106 00:06:19,110 --> 00:06:20,920 is tetraplegic. 107 00:06:20,920 --> 00:06:24,940 But we often mix Latin and Greek in these words. 108 00:06:24,940 --> 00:06:28,030 So quadriplegic is actually more commonly used. 109 00:06:32,630 --> 00:06:35,240 So you get a brain that's disconnected 110 00:06:35,240 --> 00:06:40,090 from the major motor output below the head, 111 00:06:40,090 --> 00:06:43,770 loses control of all four limbs. 112 00:06:43,770 --> 00:06:49,710 He does eventually recover reflex control. 113 00:06:49,710 --> 00:06:52,980 Of course the spinal reflex pathways are intact. 114 00:06:52,980 --> 00:06:55,940 He loses the spinal reflex for a while. 115 00:06:55,940 --> 00:06:58,720 That's, as we know, a diaschisic effect. 116 00:06:58,720 --> 00:07:01,470 You remove so much excitatory input 117 00:07:01,470 --> 00:07:03,820 from those neurons in the reflex pathways 118 00:07:03,820 --> 00:07:05,500 that they don't even function. 119 00:07:05,500 --> 00:07:07,100 The reflexes don't function. 120 00:07:07,100 --> 00:07:08,640 But they come back. 121 00:07:08,640 --> 00:07:11,710 And often they become even hyperactive, 122 00:07:11,710 --> 00:07:15,010 because of sprouting and denervations, 123 00:07:15,010 --> 00:07:20,400 super sensitivity, which are the major reasons 124 00:07:20,400 --> 00:07:21,990 you get recovery of the reflexes. 125 00:07:28,320 --> 00:07:32,270 They can think that they want to move. 126 00:07:32,270 --> 00:07:35,710 They're able to move in their minds. 127 00:07:35,710 --> 00:07:38,820 And we know that, because you can 128 00:07:38,820 --> 00:07:41,180 record with imaging methods. 129 00:07:41,180 --> 00:07:42,870 And that's what this figure is about. 130 00:07:42,870 --> 00:07:43,710 It's in the book. 131 00:07:48,010 --> 00:07:57,660 It shows here patients with-- I've forgotten now 132 00:07:57,660 --> 00:07:59,090 if one of these is a control. 133 00:07:59,090 --> 00:07:59,710 It should be. 134 00:07:59,710 --> 00:08:01,450 This should be the control. 135 00:08:01,450 --> 00:08:05,500 But anyway you can see that in the patients 136 00:08:05,500 --> 00:08:09,730 they are able to activate parts of the motor cortex. 137 00:08:09,730 --> 00:08:11,700 If they're trying to move, you ask 138 00:08:11,700 --> 00:08:15,550 them to try to move your right forearm. 139 00:08:15,550 --> 00:08:17,590 And the right forearm area of the cortex 140 00:08:17,590 --> 00:08:20,920 will increase in its activity. 141 00:08:20,920 --> 00:08:23,610 And similarly for other body parts, 142 00:08:23,610 --> 00:08:27,260 so they're able to map those areas just 143 00:08:27,260 --> 00:08:34,610 by getting the voluntary intention to move. 144 00:08:34,610 --> 00:08:36,750 But they don't move, because there's 145 00:08:36,750 --> 00:08:39,020 no way for these descending pathways 146 00:08:39,020 --> 00:08:42,600 to activate the motor neurons. 147 00:08:42,600 --> 00:08:46,610 So of course this big question remains. 148 00:08:46,610 --> 00:08:52,740 Is there any way to get those long pathways to reconnect? 149 00:08:52,740 --> 00:08:55,420 And people have worked on various ways 150 00:08:55,420 --> 00:08:59,230 to give such people some movement by artificial means. 151 00:08:59,230 --> 00:09:01,820 And there are ways that are being developed 152 00:09:01,820 --> 00:09:07,290 as you know, and get even some speaking ability in people 153 00:09:07,290 --> 00:09:08,840 that have lost these movements. 154 00:09:08,840 --> 00:09:15,380 But because of the deterioration of bodily functions 155 00:09:15,380 --> 00:09:19,740 that occurs in these kind of people, 156 00:09:19,740 --> 00:09:23,180 they usually don't live real long lives after that. 157 00:09:26,680 --> 00:09:31,650 Can you think of a famous actor that this happened to due 158 00:09:31,650 --> 00:09:34,300 to a horse accident? 159 00:09:34,300 --> 00:09:38,215 Not all that long ago, Christopher Reeve, 160 00:09:38,215 --> 00:09:43,920 the guy that played Superman in the long series 161 00:09:43,920 --> 00:09:45,270 of Superman movies. 162 00:09:45,270 --> 00:09:50,290 So he's very well known, from both films and TV. 163 00:09:54,060 --> 00:09:56,230 And they established, the Reeves, 164 00:09:56,230 --> 00:10:00,490 established the foundation to support work on regeneration. 165 00:10:03,090 --> 00:10:03,770 I met them. 166 00:10:03,770 --> 00:10:09,450 I talked mostly to Christopher Reeve's wife 167 00:10:09,450 --> 00:10:13,800 about the-- I was still pretty early on in the research 168 00:10:13,800 --> 00:10:16,330 on regeneration. 169 00:10:16,330 --> 00:10:19,110 It was after that that we developed these two methods 170 00:10:19,110 --> 00:10:23,405 of getting some vision back in animals using 171 00:10:23,405 --> 00:10:25,500 the visual systems model, which is easier 172 00:10:25,500 --> 00:10:28,210 to work with than the spinal cord. 173 00:10:28,210 --> 00:10:30,170 But now it is starting to be done, 174 00:10:30,170 --> 00:10:32,305 similar things with spinal cord, as well. 175 00:10:34,920 --> 00:10:39,265 Although as I was saying to some of you who 176 00:10:39,265 --> 00:10:41,460 talked to me after the class. 177 00:10:41,460 --> 00:10:43,280 These things are very slow to move 178 00:10:43,280 --> 00:10:47,680 into regular clinical practice. 179 00:10:47,680 --> 00:10:49,570 All right. 180 00:10:49,570 --> 00:10:54,910 A couple more topics here on these pathways. 181 00:10:54,910 --> 00:10:59,410 First of all, what do we mean by the sensory motor amalgam 182 00:10:59,410 --> 00:11:01,220 hypothesis? 183 00:11:01,220 --> 00:11:05,120 By amalgam, we mean amalgamation of the primary sensory area 184 00:11:05,120 --> 00:11:07,140 and the primary motor area. 185 00:11:07,140 --> 00:11:10,070 There are animals, especially the Virginia opossum, 186 00:11:10,070 --> 00:11:12,850 when you can't really separate them. 187 00:11:12,850 --> 00:11:16,940 That is if you map primary somatosensory cortex, 188 00:11:16,940 --> 00:11:20,310 and then you use the method of stimulation, 189 00:11:20,310 --> 00:11:23,140 define where the low threshold areas are 190 00:11:23,140 --> 00:11:25,080 in the cortex for getting movement, 191 00:11:25,080 --> 00:11:29,700 you find it just overlaps with S1, somatosensory area one. 192 00:11:32,250 --> 00:11:35,330 Well how do you know? 193 00:11:35,330 --> 00:11:37,930 Is there any purely anatomical method 194 00:11:37,930 --> 00:11:41,740 not using stimulation to map those? 195 00:11:47,280 --> 00:11:50,330 Then there's a couple other topics here I'll go over. 196 00:11:50,330 --> 00:11:52,080 So that's this question. 197 00:11:52,080 --> 00:11:58,480 And basically this is my figure about that. 198 00:11:58,480 --> 00:12:00,900 You do it by mapping the projections 199 00:12:00,900 --> 00:12:03,660 of the thalamic nuclei that project to this area. 200 00:12:03,660 --> 00:12:07,940 So if you take a human, a monkey or another primate 201 00:12:07,940 --> 00:12:12,550 like the galago, you'll find that the ventral posterior 202 00:12:12,550 --> 00:12:18,470 nucleus that gets the input from spinal thalamic tract 203 00:12:18,470 --> 00:12:21,515 from the medial lemniscus, this meta-sensory input, 204 00:12:21,515 --> 00:12:25,230 it projects to primary somatosensory cortex. 205 00:12:25,230 --> 00:12:27,820 It also projects to a second somatosensory area. 206 00:12:27,820 --> 00:12:30,520 But we don't show that here. 207 00:12:30,520 --> 00:12:33,070 And then the nucleus just in front of it, 208 00:12:33,070 --> 00:12:36,060 the ventral lateral nucleus, and there's one more-- 209 00:12:36,060 --> 00:12:38,140 the ventral anterior nucleus. 210 00:12:38,140 --> 00:12:42,210 The ventral lateral nucleus provides the primary input 211 00:12:42,210 --> 00:12:44,770 to motor one, motor cortex. 212 00:12:44,770 --> 00:12:47,540 It's just in front of the primary somatosensory cortex. 213 00:12:47,540 --> 00:12:50,780 And these two areas are quite separate 214 00:12:50,780 --> 00:12:57,990 in these large primates, even some of the smaller ones. 215 00:13:00,620 --> 00:13:02,950 But if you look at the rat, you'll find well, 216 00:13:02,950 --> 00:13:03,870 it's pretty similar. 217 00:13:03,870 --> 00:13:07,250 But there's an area there behind the representation 218 00:13:07,250 --> 00:13:08,570 where the two areas do overlap. 219 00:13:11,550 --> 00:13:17,440 Meaning that the VP and the VL both project to that area. 220 00:13:17,440 --> 00:13:19,520 If you look at the Virginia opossum, 221 00:13:19,520 --> 00:13:25,130 they overlap almost completely the area 222 00:13:25,130 --> 00:13:30,360 where the ventral posterior nucleus projects, 223 00:13:30,360 --> 00:13:32,890 overlaps completely with areas that 224 00:13:32,890 --> 00:13:36,160 the ventral lateral nucleus projects. 225 00:13:36,160 --> 00:13:37,750 So there's an amalgamation. 226 00:13:37,750 --> 00:13:40,290 They do have a separate ventral posterior 227 00:13:40,290 --> 00:13:43,730 nucleus and ventral lateral nucleus. 228 00:13:43,730 --> 00:13:47,060 They're segregated-- or no, they're 229 00:13:47,060 --> 00:13:49,440 segregated in the thalamus. 230 00:13:49,440 --> 00:13:52,920 But in the cortex, it's the same area. 231 00:13:52,920 --> 00:13:56,470 They just project in an overlapping way. 232 00:13:56,470 --> 00:14:00,530 In the brush-tailed possum, pretty similar to in some 233 00:14:00,530 --> 00:14:02,770 ways to the Virginia opossum, but notice 234 00:14:02,770 --> 00:14:06,070 that there's a large area where they are overlapping. 235 00:14:06,070 --> 00:14:08,500 But there's also a pretty sizable area 236 00:14:08,500 --> 00:14:13,010 where there's a somatosensory area that's 237 00:14:13,010 --> 00:14:15,360 not part of the motor cortex. 238 00:14:15,360 --> 00:14:17,570 I mean there's a small area of motor cortex 239 00:14:17,570 --> 00:14:21,390 that's separate from this somatosensory area. 240 00:14:21,390 --> 00:14:24,350 So you get these differences. 241 00:14:24,350 --> 00:14:27,700 So we're pretty sure that the motor cortex, primary motor 242 00:14:27,700 --> 00:14:31,330 cortex, evolved out of somatosensory areas, 243 00:14:31,330 --> 00:14:34,320 and was probably a separate somatosensory 244 00:14:34,320 --> 00:14:38,410 area that became specialized in its descending projections. 245 00:14:38,410 --> 00:14:42,230 All the cortical areas have descending projections. 246 00:14:42,230 --> 00:14:44,350 And most of them do control movement, even 247 00:14:44,350 --> 00:14:46,720 the visual cortex controls movement. 248 00:14:46,720 --> 00:14:49,530 It projects directly to the tectum, for example. 249 00:14:49,530 --> 00:14:54,330 So it can control eye and head movement, quite apart 250 00:14:54,330 --> 00:14:58,000 from-- you don't need motor cortex to get movement 251 00:14:58,000 --> 00:15:00,770 from the visual cortex. 252 00:15:00,770 --> 00:15:03,450 Don't think of motor-- motor cortex are not motor neurons. 253 00:15:03,450 --> 00:15:06,420 It's just a specialized meta-sensory area 254 00:15:06,420 --> 00:15:09,420 that's developed these long direct connections 255 00:15:09,420 --> 00:15:10,550 to the spinal cord. 256 00:15:13,250 --> 00:15:16,700 The last thing is this correlation 257 00:15:16,700 --> 00:15:22,030 of cortical projections with manual dexterity. 258 00:15:25,770 --> 00:15:27,650 And the first thing we look at is just 259 00:15:27,650 --> 00:15:32,350 comparing the volume of neocortex in various animals 260 00:15:32,350 --> 00:15:35,850 with the projections to the cord. 261 00:15:35,850 --> 00:15:41,980 Either how far down in the cord they project, 262 00:15:41,980 --> 00:15:45,680 do they go all the way down to the laminae where the motor 263 00:15:45,680 --> 00:15:49,245 neurons are, or are they only more dorsal? 264 00:15:52,520 --> 00:15:54,280 And sorry. 265 00:15:54,280 --> 00:15:59,270 These are-- layer 10 here is where the-- 10 and 9 are 266 00:15:59,270 --> 00:16:01,290 where the motor neurons are. 267 00:16:01,290 --> 00:16:04,180 8, there are the axial neurons. 268 00:16:06,790 --> 00:16:09,760 These don't contain any motor neurons at all. 269 00:16:09,760 --> 00:16:11,420 And you can see there are animals 270 00:16:11,420 --> 00:16:13,650 where there are no cortical axons 271 00:16:13,650 --> 00:16:15,912 going to the areas of motor neurons. 272 00:16:15,912 --> 00:16:20,720 And there's a number of animals though, where they do go there. 273 00:16:20,720 --> 00:16:27,100 They are the ones with greater-- that spinal projection is 274 00:16:27,100 --> 00:16:31,270 correlated, as other studies show, with their dexterity. 275 00:16:31,270 --> 00:16:32,820 Let's see this one. 276 00:16:32,820 --> 00:16:34,675 Well this one just is another measure 277 00:16:34,675 --> 00:16:35,781 of penetration of a cord. 278 00:16:35,781 --> 00:16:37,780 But here they're looking at something different, 279 00:16:37,780 --> 00:16:42,690 how far down the cord the axons of pyramidal tract go. 280 00:16:42,690 --> 00:16:45,600 This is the caudal most cord, [? casidual ?] area. 281 00:16:45,600 --> 00:16:48,750 This is the sacral area, lower lumbar. 282 00:16:48,750 --> 00:16:51,400 So these are the areas furthest down the cord. 283 00:16:51,400 --> 00:16:55,030 So you need the longest axons from cortex. 284 00:16:55,030 --> 00:16:59,700 And you can see if you're an armadillo or a tree shrew, 285 00:16:59,700 --> 00:17:02,595 the primal tract never projects to the caudalmost cord. 286 00:17:05,790 --> 00:17:10,770 Whereas a few of these animals with the greater dexterity, 287 00:17:10,770 --> 00:17:14,529 like humans and monkeys these are other monkeys, 288 00:17:14,529 --> 00:17:17,950 it goes all the way down to the [? casidual ?] cord. 289 00:17:17,950 --> 00:17:20,500 And then the correlations with their dexterity, 290 00:17:20,500 --> 00:17:22,520 they're not perfect, but if you have 291 00:17:22,520 --> 00:17:24,770 some index of measuring how dexterous 292 00:17:24,770 --> 00:17:26,640 they are with their hands, you'll 293 00:17:26,640 --> 00:17:30,120 find that there is a correlation with the deepest 294 00:17:30,120 --> 00:17:31,490 spinal laminae. 295 00:17:31,490 --> 00:17:34,160 And if you find the axons terminating in the lowest 296 00:17:34,160 --> 00:17:36,600 spinal segment, where do they go? 297 00:17:36,600 --> 00:17:38,790 The animals with the greatest dexterity, 298 00:17:38,790 --> 00:17:41,560 this group here, are the ones that 299 00:17:41,560 --> 00:17:45,630 have the most penetration in the cord. 300 00:17:45,630 --> 00:17:55,900 And in general, the larger the cortex is, as the cortex grows, 301 00:17:55,900 --> 00:17:59,790 it becomes not just bigger. 302 00:17:59,790 --> 00:18:03,800 The spinal cord doesn't grow at the same rate. 303 00:18:03,800 --> 00:18:09,400 So the cord, this neocortex, is relatively much larger 304 00:18:09,400 --> 00:18:14,570 than the cord in these animals with the highest dexterity, 305 00:18:14,570 --> 00:18:24,380 with humans having the greatest relative size of the neocortex. 306 00:18:24,380 --> 00:18:26,040 And what do we call that rule? 307 00:18:26,040 --> 00:18:31,250 That the larger a structure, the more connected it is. 308 00:18:31,250 --> 00:18:35,600 It was first enunciated by Deacon. 309 00:18:35,600 --> 00:18:36,950 So we call it Deacon's Rule. 310 00:18:36,950 --> 00:18:41,320 It's a general rule in comparative neurology 311 00:18:41,320 --> 00:18:44,090 that when the structure grows really big, 312 00:18:44,090 --> 00:18:46,000 it has more connections. 313 00:18:46,000 --> 00:18:48,330 So similarly, the optic tectum becomes 314 00:18:48,330 --> 00:18:50,290 very big in some species. 315 00:18:50,290 --> 00:18:52,210 And if you look in those species, 316 00:18:52,210 --> 00:18:54,840 according to this rule, you're going to find more connections. 317 00:18:54,840 --> 00:18:56,300 So when the tectum grew very big, 318 00:18:56,300 --> 00:19:00,400 you have more projections even to the thalamus from the tectum 319 00:19:00,400 --> 00:19:01,290 and to the cord. 320 00:19:01,290 --> 00:19:03,488 Yes? 321 00:19:03,488 --> 00:19:06,800 AUDIENCE: Are there some exceptions to that? 322 00:19:06,800 --> 00:19:07,980 PROFESSOR: Yeah. 323 00:19:07,980 --> 00:19:09,490 There are some exceptions. 324 00:19:09,490 --> 00:19:13,620 But it's been looked at in-- it's not 325 00:19:13,620 --> 00:19:16,960 been looked at for all structures. 326 00:19:16,960 --> 00:19:20,130 Like is it-- and it seems to hold 327 00:19:20,130 --> 00:19:23,360 when the differences in size are very big. 328 00:19:23,360 --> 00:19:28,330 When they're not so big, it's not a perfect correlation. 329 00:19:28,330 --> 00:19:28,830 All right. 330 00:19:28,830 --> 00:19:30,920 Good question. 331 00:19:30,920 --> 00:19:33,430 And this just shows various studies. 332 00:19:33,430 --> 00:19:36,050 I just included a bunch of them here, 333 00:19:36,050 --> 00:19:40,250 where they're showing where the corticospinal neurons are 334 00:19:40,250 --> 00:19:41,220 in the cortex. 335 00:19:41,220 --> 00:19:46,820 They're basically in the motor areas, 336 00:19:46,820 --> 00:19:50,520 and the somatosensory areas, both. 337 00:19:50,520 --> 00:19:54,750 Somatosensory areas tend not to project to the motor neurons. 338 00:19:54,750 --> 00:19:59,330 They project to the dorsal horn, and the motor areas 339 00:19:59,330 --> 00:20:03,190 project more to the ventral horn and intermediate layers 340 00:20:03,190 --> 00:20:03,716 of the cord. 341 00:20:06,540 --> 00:20:10,700 It looks like animals like rhesus monkey here have more. 342 00:20:10,700 --> 00:20:13,760 But that's-- look at the scale. 343 00:20:13,760 --> 00:20:17,610 Here are the smaller animals. 344 00:20:17,610 --> 00:20:21,410 They all represent one centimeter. 345 00:20:21,410 --> 00:20:28,160 So to really compare the rhesus monkey here with one of these, 346 00:20:28,160 --> 00:20:31,580 you would have to blow this up so the brain was bigger 347 00:20:31,580 --> 00:20:38,900 than the page here, to make the scale match. 348 00:20:38,900 --> 00:20:44,320 So you can't really see any indication of Deacon's Rule. 349 00:20:44,320 --> 00:20:46,300 But in fact, if you measure, if you 350 00:20:46,300 --> 00:20:48,520 count the number of corticospinal neurons, 351 00:20:48,520 --> 00:20:51,562 it's very strongly correlated with the total size 352 00:20:51,562 --> 00:20:52,270 of the neocortex. 353 00:20:57,130 --> 00:21:05,440 So I have a figure in the book that I 354 00:21:05,440 --> 00:21:07,560 didn't put in these slides. 355 00:21:07,560 --> 00:21:11,330 But it's fairly recent work that shows that there's really 356 00:21:11,330 --> 00:21:15,670 two separate motor regions in the motor cortex. 357 00:21:15,670 --> 00:21:20,170 They say the more caudal region is newer. 358 00:21:20,170 --> 00:21:22,880 How is it different from the older regions? 359 00:21:22,880 --> 00:21:24,130 They're both motor cortex. 360 00:21:24,130 --> 00:21:26,580 And you can stimulate both areas and get 361 00:21:26,580 --> 00:21:29,897 movement of the same body parts. 362 00:21:29,897 --> 00:21:30,730 So what's different? 363 00:21:34,370 --> 00:21:36,730 Did you read it? 364 00:21:36,730 --> 00:21:39,255 You've got to read it if you expect to do well. 365 00:21:42,157 --> 00:21:43,990 You got to read it more than once, actually. 366 00:21:46,690 --> 00:21:48,180 What's the difference? 367 00:21:48,180 --> 00:21:51,485 The difference is does the area contain 368 00:21:51,485 --> 00:21:55,180 neurons that project direct to motor neurons, 369 00:21:55,180 --> 00:21:57,100 rather than just to the interneurons. 370 00:21:57,100 --> 00:22:00,320 Remember I said the dominant connection to the cord 371 00:22:00,320 --> 00:22:04,539 isn't directly to motor neurons, even for a motor cortex. 372 00:22:04,539 --> 00:22:06,455 The dominant connection is to the interneurons 373 00:22:06,455 --> 00:22:09,430 that connect to the motor neurons. 374 00:22:09,430 --> 00:22:10,880 But there is an area. 375 00:22:10,880 --> 00:22:17,000 It's the more caudal area in the motor-- 376 00:22:17,000 --> 00:22:21,020 the strip of motor cortex. 377 00:22:21,020 --> 00:22:25,145 We're talking about this strip here. 378 00:22:25,145 --> 00:22:34,300 There you see it in the-- so you don't 379 00:22:34,300 --> 00:22:39,080 see any indication of that in these pictures, 380 00:22:39,080 --> 00:22:42,130 like in the marmoset here. 381 00:22:42,130 --> 00:22:44,780 But this would be a somatosensory area. 382 00:22:44,780 --> 00:22:46,560 This would be the motor area. 383 00:22:46,560 --> 00:22:49,582 There's a more rostral area, and a more caudal area. 384 00:22:49,582 --> 00:22:51,710 The more caudal area will contain 385 00:22:51,710 --> 00:22:55,790 the ones direct to the motor neurons. 386 00:22:55,790 --> 00:22:59,650 And that will vary a bit in size in different species. 387 00:23:03,295 --> 00:23:04,720 AUDIENCE: Is that all animals? 388 00:23:04,720 --> 00:23:06,620 Or does that start at-- 389 00:23:06,620 --> 00:23:10,544 PROFESSOR: These are maps that show all of the neurons. 390 00:23:10,544 --> 00:23:14,270 AUDIENCE: But that-- so that's in rodents and everything else, 391 00:23:14,270 --> 00:23:15,520 or it's not, or it's just in-- 392 00:23:15,520 --> 00:23:17,270 PROFESSOR: Yeah. 393 00:23:17,270 --> 00:23:20,610 There aren't so many studies that can really-- that have 394 00:23:20,610 --> 00:23:23,450 mapped exactly how many neurons there are. 395 00:23:23,450 --> 00:23:25,570 It's not easy to study. 396 00:23:25,570 --> 00:23:28,310 You see, when you just study projections 397 00:23:28,310 --> 00:23:31,930 you can look to see if there are axons that 398 00:23:31,930 --> 00:23:34,810 appear to be right in the motor neuron area. 399 00:23:34,810 --> 00:23:37,150 And that's about the only way we have of mapping it. 400 00:23:37,150 --> 00:23:40,405 And you do find them even in-- in all these species. 401 00:23:43,300 --> 00:23:44,590 All right. 402 00:23:44,590 --> 00:23:48,310 But there is-- there appears to be a lot more of them 403 00:23:48,310 --> 00:23:50,220 in the large primates. 404 00:23:53,420 --> 00:23:55,410 I have a last question here. 405 00:23:55,410 --> 00:23:57,470 Does anybody want to try to answer it? 406 00:23:57,470 --> 00:23:59,250 What's the highest level of motor control? 407 00:24:02,890 --> 00:24:07,450 To answer it, you've got to define what you mean by higher. 408 00:24:07,450 --> 00:24:09,180 Perhaps a more interesting question 409 00:24:09,180 --> 00:24:13,500 is one-- that's certainly an interesting question. 410 00:24:13,500 --> 00:24:18,480 Does movement begin with activity in the motor cortex? 411 00:24:18,480 --> 00:24:20,650 Probably not, right? 412 00:24:20,650 --> 00:24:23,100 What makes us want to move? 413 00:24:23,100 --> 00:24:26,245 Some motivation, right? 414 00:24:26,245 --> 00:24:28,185 AUDIENCE: I think it's in chapter 15 415 00:24:28,185 --> 00:24:30,610 that it's talking about what endogenous [INAUDIBLE]. 416 00:24:33,580 --> 00:24:35,890 PROFESSOR: That's one way you could start. 417 00:24:35,890 --> 00:24:38,555 So where would you find endogenous activity? 418 00:24:43,540 --> 00:24:45,310 Where would you find activity that's 419 00:24:45,310 --> 00:24:49,860 varying over time that's not originating 420 00:24:49,860 --> 00:24:51,083 outside the organism? 421 00:24:56,180 --> 00:24:57,940 Anybody? 422 00:24:57,940 --> 00:25:01,540 Probably the activity that corresponds 423 00:25:01,540 --> 00:25:05,690 to changing activity, with changing motivational levels. 424 00:25:08,430 --> 00:25:11,440 Yes, we do get a little hungrier when we see good food. 425 00:25:11,440 --> 00:25:11,990 That's true. 426 00:25:11,990 --> 00:25:13,440 That's a sensory effect. 427 00:25:13,440 --> 00:25:15,360 But we also get hunger just because we 428 00:25:15,360 --> 00:25:17,040 haven't eaten for a long time. 429 00:25:17,040 --> 00:25:20,400 That comes from internal instincts within our bodies. 430 00:25:20,400 --> 00:25:23,600 So in the sense it's endogenous to the organism. 431 00:25:23,600 --> 00:25:25,085 It doesn't mean there's no stimuli. 432 00:25:25,085 --> 00:25:26,285 It's coming from somewhere. 433 00:25:31,340 --> 00:25:35,675 So I answered the question here. 434 00:25:38,440 --> 00:25:40,200 I asked that last question. 435 00:25:40,200 --> 00:25:42,960 Why is motor cortex become so dominant 436 00:25:42,960 --> 00:25:48,070 in humans and in monkeys, and apes? 437 00:25:48,070 --> 00:25:52,670 I don't think it's only because of the striatal connections. 438 00:25:52,670 --> 00:25:57,400 And all of these areas project heavily to the corpus striatum, 439 00:25:57,400 --> 00:26:00,429 important for the learning of habits. 440 00:26:00,429 --> 00:26:02,970 I don't think it's because of the direct projections to motor 441 00:26:02,970 --> 00:26:05,980 neurons either. 442 00:26:05,980 --> 00:26:08,840 I think it's because of its close connections 443 00:26:08,840 --> 00:26:15,470 from the prefrontal areas of cortex 444 00:26:15,470 --> 00:26:21,760 that contains neurons whose firing is anticipating what's 445 00:26:21,760 --> 00:26:23,500 about to happen. 446 00:26:23,500 --> 00:26:25,970 So in the frontal eye fields there, 447 00:26:25,970 --> 00:26:28,340 part of the prefrontal cortex, caudal part 448 00:26:28,340 --> 00:26:31,940 the prefrontal cortex, you have neurons that fire 449 00:26:31,940 --> 00:26:36,300 in anticipation of where you expect something to be. 450 00:26:36,300 --> 00:26:36,980 So we move. 451 00:26:36,980 --> 00:26:39,724 We say well I move voluntarily to there. 452 00:26:39,724 --> 00:26:41,390 Well you were expecting something there. 453 00:26:41,390 --> 00:26:44,980 So you move your eyes there. 454 00:26:44,980 --> 00:26:45,855 We call it voluntary. 455 00:26:50,450 --> 00:26:52,770 That kind of activity from various parts 456 00:26:52,770 --> 00:26:56,820 of the prefrontal cortex reaches motor cortex. 457 00:26:56,820 --> 00:26:58,990 That's how it exerts its influence. 458 00:26:58,990 --> 00:27:01,740 The prefrontal cortex does not project directly 459 00:27:01,740 --> 00:27:04,090 to the spinal cord, and control these movements. 460 00:27:04,090 --> 00:27:06,070 It goes through motor cortex. 461 00:27:06,070 --> 00:27:08,400 And I think one reason the motor cortex became 462 00:27:08,400 --> 00:27:10,980 so dominant is because it's getting 463 00:27:10,980 --> 00:27:13,750 that input from the prefrontal areas. 464 00:27:13,750 --> 00:27:16,580 And it's most dominant in the animals with a larger 465 00:27:16,580 --> 00:27:17,490 prefrontal cortex. 466 00:27:17,490 --> 00:27:18,770 Yes? 467 00:27:18,770 --> 00:27:21,710 AUDIENCE: So maybe this is really off track. 468 00:27:21,710 --> 00:27:28,100 But did they find motor deficits in the [INAUDIBLE] patients? 469 00:27:28,100 --> 00:27:30,870 PROFESSOR: It's hard to call them motor deficits. 470 00:27:30,870 --> 00:27:35,520 But you have incredible changes in the way they behave. 471 00:27:38,220 --> 00:27:41,460 Probably the most dramatic are they lose normal inhibitions. 472 00:27:44,130 --> 00:27:46,370 It's almost like a release of activity, 473 00:27:46,370 --> 00:27:51,280 because there are other influences too on motor cortex. 474 00:27:51,280 --> 00:27:54,910 And movement doesn't all go through motor cortex. 475 00:27:54,910 --> 00:27:57,610 But what we call voluntary movement 476 00:27:57,610 --> 00:27:59,260 does go through motor cortex. 477 00:27:59,260 --> 00:28:02,220 It doesn't originate there. 478 00:28:02,220 --> 00:28:04,760 It originates usually in the limbic system, 479 00:28:04,760 --> 00:28:06,690 but it's these association areas that 480 00:28:06,690 --> 00:28:09,460 include the prefrontal areas, prefrontal association 481 00:28:09,460 --> 00:28:15,215 areas, that seem to be where expected things control 482 00:28:15,215 --> 00:28:16,560 our movements. 483 00:28:16,560 --> 00:28:17,060 All right. 484 00:28:17,060 --> 00:28:23,270 Let's say a little bit about temporal patterns, 485 00:28:23,270 --> 00:28:25,340 and about brain states. 486 00:28:25,340 --> 00:28:27,430 If we don't have time, we can say a little bit 487 00:28:27,430 --> 00:28:28,830 about brain states on Monday. 488 00:28:28,830 --> 00:28:32,050 But I'm going to spend a lot of that hour just reviewing 489 00:28:32,050 --> 00:28:35,600 to help you get ready for the midterm. 490 00:28:35,600 --> 00:28:37,990 But let's just talk briefly about temporal patterns. 491 00:28:37,990 --> 00:28:49,780 And this is an interesting area, because the explanations 492 00:28:49,780 --> 00:28:53,620 have been generated as much from theory as 493 00:28:53,620 --> 00:28:55,140 from actual experiments. 494 00:28:55,140 --> 00:29:01,010 There are experiments related to this. 495 00:29:05,280 --> 00:29:07,960 We usually start by talking about rhythmic output, 496 00:29:07,960 --> 00:29:10,340 and timing the simplest kind of temporal patterns, 497 00:29:10,340 --> 00:29:13,760 it's a rhythmic pattern. 498 00:29:13,760 --> 00:29:16,150 And there are various ways that we 499 00:29:16,150 --> 00:29:20,200 can talk about how temporal patterns are generated. 500 00:29:20,200 --> 00:29:23,680 We can talk just about reflex types of connections 501 00:29:23,680 --> 00:29:25,170 that go from input to output. 502 00:29:25,170 --> 00:29:33,000 So the rhythm depends on the inputs, 503 00:29:33,000 --> 00:29:35,755 and on the timing of those pathways. 504 00:29:38,290 --> 00:29:42,660 It takes time for input to travel, 505 00:29:42,660 --> 00:29:45,870 activity to travel through the central nervous system. 506 00:29:45,870 --> 00:29:48,800 And then, of course, you can have feedback connections 507 00:29:48,800 --> 00:29:53,380 of various sorts that will generate temporal patterns. 508 00:29:53,380 --> 00:29:59,090 And you can also have endogenous activity, activity originating 509 00:29:59,090 --> 00:30:01,580 in the nervous system and even in single cells. 510 00:30:06,430 --> 00:30:09,320 So first of all, how can the concept 511 00:30:09,320 --> 00:30:13,500 of reflexes or more generally stimulus 512 00:30:13,500 --> 00:30:18,760 response connections of the sort that underlies fixed action 513 00:30:18,760 --> 00:30:22,420 patterns of innate behavior, be used 514 00:30:22,420 --> 00:30:27,280 to explain sequences that are longer than a single reflex? 515 00:30:29,950 --> 00:30:34,950 If we start with just a single reflex, 516 00:30:34,950 --> 00:30:39,200 then we have to talk about conduction time, various things 517 00:30:39,200 --> 00:30:42,090 that affect conduction time. 518 00:30:42,090 --> 00:30:45,850 If we talk about beyond the simple reflex, 519 00:30:45,850 --> 00:30:48,130 then the only way we can use that model 520 00:30:48,130 --> 00:30:50,480 is to talk about some kind of chaining. 521 00:30:50,480 --> 00:30:52,910 So let's start by that. 522 00:30:52,910 --> 00:30:56,970 And I mentioned the startle reflex. 523 00:30:56,970 --> 00:31:00,720 If there's a very loud noise, louder 524 00:31:00,720 --> 00:31:03,370 than I could produce here, because I don't have 525 00:31:03,370 --> 00:31:08,100 a good amplifier here; you get the sequence 526 00:31:08,100 --> 00:31:11,330 of movements that are always the same. 527 00:31:11,330 --> 00:31:14,570 The eyes blink first. 528 00:31:14,570 --> 00:31:18,290 And then you get contraction of the facial muscles. 529 00:31:18,290 --> 00:31:20,180 Then you get neck flexion. 530 00:31:20,180 --> 00:31:21,950 Then you get arm flexion. 531 00:31:21,950 --> 00:31:26,350 You see this around explosions. 532 00:31:26,350 --> 00:31:30,130 And with a loud explosion you even get leg flexions. 533 00:31:30,130 --> 00:31:31,520 But it's always in that sequence. 534 00:31:34,160 --> 00:31:38,540 And you can explain that timing by the length of pathways, 535 00:31:38,540 --> 00:31:43,020 the fiber size, which makes changes to conduction time. 536 00:31:43,020 --> 00:31:46,640 You can explain it by synaptic delays in the pathway. 537 00:31:46,640 --> 00:31:49,135 You can explain it by temporal summation times. 538 00:31:53,300 --> 00:31:57,415 And the startle reflex has been a reflex 539 00:31:57,415 --> 00:31:59,390 that's been studied in this way. 540 00:31:59,390 --> 00:32:03,950 And you get this-- you can explain it just 541 00:32:03,950 --> 00:32:09,376 in terms of these timing through the stimulus to response 542 00:32:09,376 --> 00:32:09,875 pathway. 543 00:32:13,680 --> 00:32:16,700 But when we get to chaining, it's 544 00:32:16,700 --> 00:32:18,550 been very difficult to prove there's 545 00:32:18,550 --> 00:32:21,820 any real chaining of reflexes. 546 00:32:21,820 --> 00:32:24,320 But when it comes to fixed-action patterns, 547 00:32:24,320 --> 00:32:25,270 it's much easier. 548 00:32:27,970 --> 00:32:32,520 And then we'll talk about the swallowing reflex, so-called 549 00:32:32,520 --> 00:32:33,380 swallowing reflex. 550 00:32:33,380 --> 00:32:39,150 As it turns out it's not a reflex in the usual sense. 551 00:32:39,150 --> 00:32:44,095 I like Tinbergen's example of fixed action patterns, where 552 00:32:44,095 --> 00:32:46,250 you have a whole sequence of movements. 553 00:32:46,250 --> 00:32:48,230 But it actually involves two different animals. 554 00:32:48,230 --> 00:32:52,230 So for example it starts with a female. 555 00:32:52,230 --> 00:32:53,260 The female appears. 556 00:32:53,260 --> 00:32:55,630 She's got the swollen belly which 557 00:32:55,630 --> 00:32:58,580 is the key stimulus for triggering 558 00:32:58,580 --> 00:33:03,410 the male response, which is if he's in a courtship mood, 559 00:33:03,410 --> 00:33:06,020 he will start this-- they call it the zigzag dance. 560 00:33:06,020 --> 00:33:12,880 A particular way he moves to get the female to approach him. 561 00:33:12,880 --> 00:33:17,660 And when she does, then he's swims toward his nest, 562 00:33:17,660 --> 00:33:18,720 and she follows him. 563 00:33:18,720 --> 00:33:22,220 So that's her next response. 564 00:33:22,220 --> 00:33:23,510 She follows him. 565 00:33:23,510 --> 00:33:25,550 And then when he gets to the nest, 566 00:33:25,550 --> 00:33:28,390 he adopts a particular posture that 567 00:33:28,390 --> 00:33:30,420 causes her to enter the nest. 568 00:33:30,420 --> 00:33:32,620 He doesn't enter it first. 569 00:33:32,620 --> 00:33:34,780 He changed his posture. 570 00:33:34,780 --> 00:33:37,895 She enters the nest. 571 00:33:40,430 --> 00:33:46,160 And then the male stimulates her in a very specific way. 572 00:33:46,160 --> 00:33:49,620 He trembles, puts his snout at her tail. 573 00:33:49,620 --> 00:33:52,050 It causes her to spawn. 574 00:33:52,050 --> 00:33:54,770 It's just an innate response. 575 00:33:54,770 --> 00:33:58,890 And when she spawns-- actually I left out 576 00:33:58,890 --> 00:34:01,750 she swims out of the nest. 577 00:34:01,750 --> 00:34:04,140 And as she swims out of the nest, he's right behind her. 578 00:34:04,140 --> 00:34:06,950 But he pauses in the nest, and fertilizes the eggs. 579 00:34:10,370 --> 00:34:11,980 They don't have sexual intercourse. 580 00:34:11,980 --> 00:34:14,690 This is a way they fertilize. 581 00:34:14,690 --> 00:34:17,429 And it's a sequence of fixed-action patterns. 582 00:34:17,429 --> 00:34:20,210 Each step is a necessary stimulus 583 00:34:20,210 --> 00:34:21,469 for triggering the next step. 584 00:34:21,469 --> 00:34:27,340 And in the book I had used that sequence 585 00:34:27,340 --> 00:34:30,560 of fixed-action patterns explanation 586 00:34:30,560 --> 00:34:32,960 for a behavior, which I've observed many times 587 00:34:32,960 --> 00:34:36,549 with Syrian hamsters when they forage for food. 588 00:34:36,549 --> 00:34:38,400 It shows the same thing. 589 00:34:38,400 --> 00:34:41,710 One fixed-action pattern follows another. 590 00:34:41,710 --> 00:34:45,360 Because one fixed-action pattern leads to a stimulus, 591 00:34:45,360 --> 00:34:47,460 that then triggers the next fixed-action pattern, 592 00:34:47,460 --> 00:34:49,260 and so on. 593 00:34:49,260 --> 00:34:52,340 And that ends with they're pushing the seeds out 594 00:34:52,340 --> 00:34:55,424 of their pouch back in their nest area. 595 00:34:55,424 --> 00:34:57,545 They push it onto a food horn. 596 00:35:01,450 --> 00:35:04,440 So then I ask you here to name a movement pattern 597 00:35:04,440 --> 00:35:07,090 in an animal or human that's largely 598 00:35:07,090 --> 00:35:10,780 under the control of the hindbrain spinal cord, that 599 00:35:10,780 --> 00:35:13,240 is centrally generated once it's triggered. 600 00:35:17,344 --> 00:35:20,740 And I want to know how it's different from a reflex, 601 00:35:20,740 --> 00:35:24,932 even though it might be called a reflex in clinical neurology. 602 00:35:24,932 --> 00:35:26,760 AUDIENCE: Like swallowing. 603 00:35:26,760 --> 00:35:29,010 PROFESSOR: Like swallowing, exactly. 604 00:35:29,010 --> 00:35:30,940 We call it the swallowing reflex. 605 00:35:30,940 --> 00:35:34,366 Why do we call it the swallowing reflex? 606 00:35:34,366 --> 00:35:38,690 You know how swallowing is triggered? 607 00:35:38,690 --> 00:35:40,985 It's triggered by a-- you actually, 608 00:35:40,985 --> 00:35:45,170 you think you trigger it voluntarily. 609 00:35:45,170 --> 00:35:47,050 But you're not triggering it directly. 610 00:35:47,050 --> 00:35:50,630 What you're doing is moving the back of your tongue, 611 00:35:50,630 --> 00:35:55,270 so you stimulate the area behind a row of papillae, 612 00:35:55,270 --> 00:35:56,750 called the circumvallate papillae 613 00:35:56,750 --> 00:36:00,380 on the back of the tongue. 614 00:36:00,380 --> 00:36:04,380 And so a doctor stimulates it if he slides a stick. 615 00:36:04,380 --> 00:36:06,780 You can trigger very easily with your finger. 616 00:36:06,780 --> 00:36:08,310 What do you get as soon as you get 617 00:36:08,310 --> 00:36:10,350 beyond that place on your tongue? 618 00:36:10,350 --> 00:36:11,330 You start gagging. 619 00:36:11,330 --> 00:36:14,260 What you're doing is trying to swallow. 620 00:36:14,260 --> 00:36:16,840 You can't swallow, because your fingers in your throat. 621 00:36:16,840 --> 00:36:20,570 And similarly with a stick, so he's simply 622 00:36:20,570 --> 00:36:25,660 triggering what he calls the swallowing reflex, or the gag 623 00:36:25,660 --> 00:36:27,065 reflex, he will call it. 624 00:36:30,820 --> 00:36:39,520 But that-- we'll come back to the other one there. 625 00:36:39,520 --> 00:36:41,835 So it's called reflex swallowing, 626 00:36:41,835 --> 00:36:48,290 or reflex deglutition, the name used by neurologists. 627 00:36:48,290 --> 00:36:50,930 It actually involves about 20 muscles 628 00:36:50,930 --> 00:36:53,400 controlled by neurons all the way 629 00:36:53,400 --> 00:36:56,640 from the midbrain to the cervical spinal cord levels, 630 00:36:56,640 --> 00:37:01,780 mostly in the hindbrain and upper most spinal cord. 631 00:37:01,780 --> 00:37:06,920 Many experiments have been done to eliminate, after one muscle 632 00:37:06,920 --> 00:37:10,670 contracts, to see which stimuli that causes. 633 00:37:10,670 --> 00:37:13,580 And you could eliminate all the sources of proprioception. 634 00:37:13,580 --> 00:37:17,830 You can even take out some of the muscles involved 635 00:37:17,830 --> 00:37:21,200 in the sequence of movements involved in swallowing, 636 00:37:21,200 --> 00:37:25,036 and the pattern will continue exactly even when 637 00:37:25,036 --> 00:37:26,410 some of the elements are missing. 638 00:37:30,980 --> 00:37:34,290 And those experiments show that it's centrally programmed. 639 00:37:34,290 --> 00:37:38,430 Once it's triggered by the key stimulus, 640 00:37:38,430 --> 00:37:41,610 it's a centrally programmed movement. 641 00:37:41,610 --> 00:37:46,650 It's a fixed-action pattern in the ethological sense. 642 00:37:46,650 --> 00:37:48,690 It even has a motivation that builds up. 643 00:37:48,690 --> 00:37:50,380 We don't pay a lot of attention to that. 644 00:37:50,380 --> 00:37:53,620 But we swallow occasionally to keep our throat lubricated. 645 00:37:53,620 --> 00:37:54,980 We don't even think about it. 646 00:37:54,980 --> 00:37:59,350 Now that you're thinking about it, you'll probably swallow. 647 00:37:59,350 --> 00:38:00,215 I'm doing it myself. 648 00:38:09,950 --> 00:38:13,245 I mentioned here name a movement pattern 649 00:38:13,245 --> 00:38:17,030 that's largely under the control of the spinal cord, 650 00:38:17,030 --> 00:38:18,940 and completely so in many species. 651 00:38:18,940 --> 00:38:22,580 We talked about that one earlier. 652 00:38:22,580 --> 00:38:26,200 The pattern-- a pattern that's almost completely 653 00:38:26,200 --> 00:38:31,580 determined, probably completely, in the spinal cord. 654 00:38:31,580 --> 00:38:37,030 In mammals it requires some external input 655 00:38:37,030 --> 00:38:41,540 to get it started, or some input from the brain. 656 00:38:41,540 --> 00:38:46,210 But it doesn't require any pattern in those inputs. 657 00:38:46,210 --> 00:38:50,286 We're just talking about the movements of locomotion. 658 00:38:50,286 --> 00:38:53,076 It's a spinally generated pattern. 659 00:38:57,510 --> 00:39:03,090 Again, it's a fixed-action pattern 660 00:39:03,090 --> 00:39:07,360 that's wired in by our genetics. 661 00:39:07,360 --> 00:39:11,410 This problem of how patterns are generated 662 00:39:11,410 --> 00:39:16,400 was what Karl Ashley called the problem of serial order 663 00:39:16,400 --> 00:39:17,880 in behavior. 664 00:39:17,880 --> 00:39:20,530 How is a sequence, an ordered sequence-- 665 00:39:20,530 --> 00:39:22,590 he used to say how do we do this? 666 00:39:22,590 --> 00:39:25,410 And he would move his hand like this. 667 00:39:25,410 --> 00:39:27,390 [INAUDIBLE] used to do that. 668 00:39:27,390 --> 00:39:28,767 How do we do that? 669 00:39:31,570 --> 00:39:35,480 And he argued, the key part of his argument 670 00:39:35,480 --> 00:39:39,780 was that many of our movements are simply 671 00:39:39,780 --> 00:39:45,380 too fast for each movement to be separately triggered by reflex. 672 00:39:45,380 --> 00:39:46,570 They're too fast. 673 00:39:46,570 --> 00:39:49,800 Our reaction times when you measure them for reflexes 674 00:39:49,800 --> 00:39:51,720 simply aren't that fast. 675 00:39:51,720 --> 00:39:54,570 He talks about the finger strokes of a musician 676 00:39:54,570 --> 00:39:58,510 can reach 16 per second. 677 00:39:58,510 --> 00:40:02,010 In passages which call for a definite and changing order 678 00:40:02,010 --> 00:40:06,340 of successive finger movements, so that 679 00:40:06,340 --> 00:40:10,390 has to central generation of movements like that. 680 00:40:10,390 --> 00:40:15,530 And there's not a lot of evidence for various centrally 681 00:40:15,530 --> 00:40:17,470 generated patterns, like grooming 682 00:40:17,470 --> 00:40:22,910 in mice we mentioned last time, John Fentress experiments. 683 00:40:22,910 --> 00:40:27,890 He asked whether, when the mouse starts grooming, well 684 00:40:27,890 --> 00:40:30,240 he is generating stimuli, right? 685 00:40:30,240 --> 00:40:32,950 So is each stimulus triggering the next movement? 686 00:40:32,950 --> 00:40:36,720 So he did things like amputate the arm, 687 00:40:36,720 --> 00:40:39,220 and trigger the grooming. 688 00:40:39,220 --> 00:40:42,610 The mouse grooms as is if the arm were there. 689 00:40:42,610 --> 00:40:44,005 He's not producing any stimuli. 690 00:40:46,840 --> 00:40:49,260 You can get rid of any source of the stimulus, 691 00:40:49,260 --> 00:40:53,160 and yet the movement goes off in the proper order. 692 00:40:53,160 --> 00:40:56,640 Egg rolling in gulls, it's the same way. 693 00:40:56,640 --> 00:41:00,050 They will roll an egg back into the nest, 694 00:41:00,050 --> 00:41:03,910 remove the egg in the middle of it, and he keeps doing it. 695 00:41:03,910 --> 00:41:07,450 He just does it as if the egg were there. 696 00:41:07,450 --> 00:41:10,700 We call those in vacuo movement patterns, 697 00:41:10,700 --> 00:41:12,910 movement patterns innate behavior 698 00:41:12,910 --> 00:41:16,885 without any stimulus that's any normal stimulus. 699 00:41:19,970 --> 00:41:22,030 And locomotion has been studied a lot. 700 00:41:22,030 --> 00:41:24,330 We know that the fin movements in fish 701 00:41:24,330 --> 00:41:25,680 are centrally generated. 702 00:41:25,680 --> 00:41:28,885 They've even found neurons that are generating those movements. 703 00:41:32,110 --> 00:41:34,320 And I mentioned locomotion in mammals. 704 00:41:34,320 --> 00:41:36,140 It does require some activation. 705 00:41:36,140 --> 00:41:38,000 But it doesn't require patterned activation. 706 00:41:40,970 --> 00:41:45,340 So how are they generated then if it's not by reflexes? 707 00:41:45,340 --> 00:41:48,680 And there's basically two kinds of patterns. 708 00:41:48,680 --> 00:41:52,110 Either there's got to be feedback in neural circuits, 709 00:41:52,110 --> 00:41:54,710 or there's got to be endogenous activity. 710 00:41:57,620 --> 00:41:59,450 Or there could be various combinations 711 00:41:59,450 --> 00:42:00,950 of those kinds of mechanisms. 712 00:42:00,950 --> 00:42:03,320 Those are the kinds we know about. 713 00:42:03,320 --> 00:42:06,820 So with feedback, you can talk about self exciting loops, 714 00:42:06,820 --> 00:42:10,260 and I put in this little diagram just to illustrate that. 715 00:42:10,260 --> 00:42:13,090 You make certain assumptions about how these neurons are 716 00:42:13,090 --> 00:42:15,530 firing, simplifying assumptions. 717 00:42:15,530 --> 00:42:18,410 And now you can have a steady input here. 718 00:42:18,410 --> 00:42:21,490 It doesn't generate any patterned output. 719 00:42:21,490 --> 00:42:25,390 But with one pulse coming in from another source, 720 00:42:25,390 --> 00:42:30,260 you could start this feedback circuit, 721 00:42:30,260 --> 00:42:36,140 and get the output here to be a series of pulses. 722 00:42:36,140 --> 00:42:37,160 How would you stop it? 723 00:42:37,160 --> 00:42:39,070 Well you'd have to either by fatigue 724 00:42:39,070 --> 00:42:43,470 or by an inhibitory input, a very simple way 725 00:42:43,470 --> 00:42:48,390 you can have a feedback circuit generating a pattern. 726 00:42:48,390 --> 00:42:51,260 This system that's been studied the most that 727 00:42:51,260 --> 00:42:55,816 is controlled by such circuits is breathing. 728 00:42:55,816 --> 00:42:57,410 There's been a number of studies. 729 00:42:57,410 --> 00:43:00,015 There's a guy here at MIT in engineering, 730 00:43:00,015 --> 00:43:03,090 named Poon that has studied breathing a lot. 731 00:43:03,090 --> 00:43:05,010 It's actually pretty complex. 732 00:43:05,010 --> 00:43:09,260 But the basic story always involves these feedback 733 00:43:09,260 --> 00:43:09,760 circuits. 734 00:43:12,490 --> 00:43:15,510 And there's many examples in our anatomical studies 735 00:43:15,510 --> 00:43:19,930 of the brain that show these loops. 736 00:43:19,930 --> 00:43:22,390 Anatomists love to talk about loops. 737 00:43:22,390 --> 00:43:25,880 That doesn't mean they always know what they do. 738 00:43:25,880 --> 00:43:28,320 But there certainly-- the nervous system 739 00:43:28,320 --> 00:43:30,950 is full of connections like this. 740 00:43:30,950 --> 00:43:32,955 And then we have endogenous activity. 741 00:43:35,860 --> 00:43:38,050 How can a neuron, a single neuron, 742 00:43:38,050 --> 00:43:40,140 generate a temporal pattern? 743 00:43:40,140 --> 00:43:42,380 This for example, is an example. 744 00:43:42,380 --> 00:43:45,260 I took this from Felix Strumwasser's work. 745 00:43:45,260 --> 00:43:48,990 He studied big neurons in the abdominal ganglion of Aplysia, 746 00:43:48,990 --> 00:43:51,720 because he could identify the same neuron in one animal 747 00:43:51,720 --> 00:43:53,070 after the other. 748 00:43:53,070 --> 00:43:57,610 And he found that they generated rhythmic activity. 749 00:43:57,610 --> 00:44:02,550 Just the-- they had a membrane potential that oscillated, 750 00:44:02,550 --> 00:44:06,110 even if you blocked the action potentials, 751 00:44:06,110 --> 00:44:07,340 they still generate. 752 00:44:07,340 --> 00:44:09,160 How does it do that? 753 00:44:09,160 --> 00:44:12,380 What in the membrane is causing that? 754 00:44:12,380 --> 00:44:14,910 They call-- they find specific areas 755 00:44:14,910 --> 00:44:19,160 in the membrane they call a pacemaker locus that generates 756 00:44:19,160 --> 00:44:22,140 these changes, particular types of molecules. 757 00:44:22,140 --> 00:44:27,220 They use energy, and they cause the membrane potential 758 00:44:27,220 --> 00:44:28,160 to oscillate. 759 00:44:28,160 --> 00:44:32,340 And of course if you don't block the action potentials when 760 00:44:32,340 --> 00:44:34,490 the depolarization is enough, you 761 00:44:34,490 --> 00:44:35,840 will trigger action potential. 762 00:44:35,840 --> 00:44:38,800 So some of those neurons then depolarize enough 763 00:44:38,800 --> 00:44:42,460 with every cycle to generate action potentials. 764 00:44:42,460 --> 00:44:46,890 And that's true of some of the very slow oscillators 765 00:44:46,890 --> 00:44:48,970 have endogenous activities like this, 766 00:44:48,970 --> 00:44:51,160 like the endogenous clock. 767 00:44:51,160 --> 00:44:53,695 Single neurons in the suprachiasmatic nucleus 768 00:44:53,695 --> 00:44:55,570 will oscillate like this. 769 00:44:55,570 --> 00:45:00,450 In this case in the Aplysia abdominal ganglion 770 00:45:00,450 --> 00:45:03,090 the rhythm was 40 seconds. 771 00:45:03,090 --> 00:45:07,050 But he claims that in that neuron 772 00:45:07,050 --> 00:45:11,300 there's also circadian rhythm that changes over 24 hours. 773 00:45:11,300 --> 00:45:15,140 I'm not convinced he recorded from them long enough 774 00:45:15,140 --> 00:45:16,884 to be sure about that. 775 00:45:16,884 --> 00:45:18,800 Because other things could have been changing. 776 00:45:18,800 --> 00:45:20,970 But there's definitely good evidence. 777 00:45:20,970 --> 00:45:24,360 [CELL PHONE RINGING] 778 00:45:24,360 --> 00:45:26,699 That just means I have to stop. 779 00:45:26,699 --> 00:45:28,240 AUDIENCE: That's your startle reflex. 780 00:45:31,007 --> 00:45:31,590 PROFESSOR: OK. 781 00:45:31,590 --> 00:45:33,220 Yeah, the startle. 782 00:45:33,220 --> 00:45:35,700 I'd like you to read the rest of this, 783 00:45:35,700 --> 00:45:38,660 and read what I say about overall state 784 00:45:38,660 --> 00:45:40,120 of the brain and its control. 785 00:45:40,120 --> 00:45:41,860 And we'll have a chance to discuss that 786 00:45:41,860 --> 00:45:44,090 a little bit on Monday. 787 00:45:44,090 --> 00:45:47,555 And then we'll spend the rest of the time reviewing.