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MITOCW | MIT9_14S09_lec16-mp3

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PROFESSOR: OK, today let's continue with the . The quiz for this week will be posted. Just a few questions. One of them might require you to do a little bit on the web, but it should be pretty easy for you to finish it by-- I'll accept them through Saturday.

We were talking about hierarchical control of local motor behavior. And I pointed out how local motor pattern controllers and initiators in the hypothalamus or sub- -- they call it the mid--- get a lot of input from the end-brain, as I show

here in blue.

And I just want to point out that this picture might lead you to believe that locomotion is always originating in the end-brain. Show it being initiated by olfactory inputs,

other kinds of sensory inputs that come in through the older pathways through the old thalamus and . And the newer pathways reaching the neocortex. But I note here that some inputs from the visual system, they actually reach that area, the

mid-brain locomotor area more directly without going through the striatum. They come through a part of the [? pretectural ?] [? legion ?].

And it's very likely that other systems do the same, but we know-- remember those lesion experiments I talked about some time ago? Animals with decerebrations where the whole end-brain was removed? They didn't initiate much locomotion at all. You'd have to push them, nudge them in various ways to get them to locomote. But of course that might be partly an artifact of that huge brain lesion you're making.

So I think there's some initiation of locomotion without too much above the mid- brain. It's been-- it's not been studied as much as these pathways shown here in the far left.

1 So this is the pathway from olfactory bulbs that goes through the ventral striatum, that then goes to this area, the caudal hypothalamus. We call that, that's the region of the hypothalamic locomotor area. And then, to this region of the caudal mid- brain, the mid-brain locomotor area. Just to show you on that diagram I've been using, of the ancestral brain, where these pathways are found. And have been found since very early evolution.

But we know the generation of the actual pattern of locomotion, control of those movements, is spinal and . It depends on [? propria ?] spinal input, from muscles and joints. It depends on tactal inputs from the limbs.

So I want to talk now a little bit about these circuits that influence locomotion in various ways. We know its execution can be modulated by reflex inputs to the directly, from the field. They come in through the dorsal roots and use propria spinal connections to reach motor neurons. But I want to say now more about these hindbrain mechanisms, coming through to the stibula nuceli, and the . Let's just take a look at what they're like.

The stibula nuclei get input through the eighth nerve. So the eighth nerve carries both auditory and vestibular input from the inner ear. The stibula nuclei are actually a collection of four different nuclei. One of them has very, very large cells. It's called

Deiters' nucleus. This nucleus gets direct input from the . It has direct projections to the spinal cord. So it's just one , the vestibular system can reach the spinal motor mechanisms. We call that the vestibular spinal track. It comes from Deiters' nucleus.

We also get pretty direct input to the motor neurons controlling eye muscles. These follow the MLF, the media longitudinal fasciculus, it's called. And you'll see that in the diagrams here. Directly connects and the ocularmotor nuclei.

So a lot of the stabilization of our eyes as we move our head-- when I do this, my eyes stay pretty much in the same position, looking out at the class. Part of that's visual, of course. I'm maintaining fixation. But even if I close my eyes and if you kept track of the position of my eyeballs, you'd see pretty much the same thing

2 happening. It's under vestibular control, not just visual control.

So these are the [? Nauder ?] pictures, where he shows the of a human as if it were transparent. And he's showing the secondary sensory cell groups and the groups of motor neurons. And I've shown the vestibular nuclei there with the blue stippling. So you can see its location there, on the rostral hindbrain.

These are the cerebellar peduncles. So that's where all the fibers come to connect the cerebellum to the brainstem. All these fibers in this really big bundle here in the side come from the . Hearing input from the cortex up to the cerebellum. That's been removed. The region there of the and the vestibular nuclei, you wouldn't see all if the cerebellum were there. So the cerebellum has to be removed to get this kind of picture.

So now let's look at the part of the cerebellum that's closely related to the vestibular system. The vestibulocerebellum. It's probably the most ancient part of the cerebellum, and it's somewhat different in its connections from the rest of the cerebellum.

These parts of the cerebellum have these peculiar names, the flocculus and the nodulus. They get direct input from the vestibular nerve. And they influence muscles of the body axis, as does this medialmost most of the deep nuclei of the cerebellum, where all the other outputs of the cerebellum come from. They come from deep nuclei. They don't come from the cortex of the cerebellum.

So I just want to show you, here's a diagrammatic top view of a cerebellum.

Probably based on the cerebellum of a cat, or a rat. And in the dark red there, and over here in the red dots, you see the vestibulocerebellum. or So that's the part that's getting the direct input there, on the sagittal picture there, it's tucked under in the back. The other structure's located medially here in the lighter, in the pink dots, we refer to as the spinocerebellum, because it's dominated by input coming from the spinal cord.

Whereas the hemisphere's the largest part-- in the large animals, anyway-- shown

3 on the small black dots, is getting its input through the pons coming from [UNINTELLIGIBLE]. So they call that the cerebrocerebellum here. It's because of that cerebellum has expanded so much in recent evolution, because with the expansion of the hemispheres the cerebellum expands along with it. But primarily in the hemispheres.

And in this picture you see the diagram here of the primary sensory neurons. Out here in the inner ear. And here comes the into the hindbrain, through the eighth nerve. And note that some of them go directly to that floccular, nodular cortex of the cerebellum without any synapse. So they're secondary sensory neurons of the vestibular system in that this part of the cerebellum here.

There's also secondary sensory cells there in the vestibular nuclei that project up to that region of the cerebellum. So you get both types of inputs to these vestibular parts of the cerebellum.

And then here we see those regions of the cerebellum projecting to the vestibular nuclei, just bypassing the vestigial nucleus. Bypassing the deep nuclei. So in these respects, the vestibular parts of the cerebellum are different from all the rest of the cerebellum. Primary sensory neurons reaching them from the vestibular system, and output cells coming directly from that cortex to the vestibular nuclei of the hindbrain, and not going to the deep nuclei here in the cerebellum.

And then those vestibular nuclei, as we mentioned, have direct projections to the spinal cord. There's a diagram of it. Calls it the vestibulospinal pathway, or tract.

And then here, of that medial longitudinal fasciculus that are connecting to the third, fourth, and sixth nerve nuclei controlling the eye muscles.

This is much too complicated at this point. I just want to show you here, this diagram of the cerebellar cortex. Which is taken from what a frontal section through the cerebellum would look like. And they've shown three deep nuclei there. That's where most of the output, with the exception of those vestibular system projections, these deep nuclei receive the output of the cortex of the cerebellum. And then they project to the rest of the brain. And this medialmost one not only connects with the 4 vestibular nuclei, but connects with the spinal cord also. Like the vestibular nucleus does. So does this vestigial nucleus. It go straight down to the cord of cerebellospinal tract. It's often called the . Not to confuse you, just that's the way neuroanatomists name it. They name if after the source and the termination.

The other projection of the cerebellum, we'll mention bit by bit as we go along.

We're not going to put any great emphasis on the cerebellum except to point out the cerebellum has enlarged as the hemispheres have enlarged. And these are just some of the basic connections. There's a lot of ascending connections that reach the cortex through the thalamus that we can mention also later when we talk about cortex.

So we've talked about the locomotor movements. They're one of the three major types of multipurpose movements, so let's say a little more now about orienting the body and head. Important for reaching the goals of locomotor approach.

We know that early controls were, we call them reflexive visual inputs reaching neurons that simply, whenever the input is novel, can trigger reflexive type movements. I don't think all of them came through the tectum. Probably the early ones went through subthalamus and pretectum. But that's an understudied area. Not very much is known about the role of these other systems. We'll mention them when we talk about visual systems, but we know most about the role of the midbrain tectum. And that's the structure where there's been an evolution of these topographic representations of the world. We know the whole retina is represented, it gets direct inputs from the retina to various parts of the tectum where there's sort of a map of a retina.

And over the tactal surface, and then there's been an evolution of auditory maps of the world too, and some other sensory in the deeper layers of the tectum that precisely match the visual map.

What do we mean by an auditory map of space? Well, we can detect space around us by the source of sounds. So when we talk about our auditory system, we'll talk a 5 little bit about how that happens. Some animals have really good ability to locate by the source of a sound. Birds of prey, for example, can do that almost as well as they can use their vision. These animals have both very good vision, very good audition. They use both of them for localizing prey. So they can detect, for example, a mouse running on a forest floor without actually being able to see him, just by the little sounds that he's making.

Now we know that that tectum gets that input. That's topographic in the way it represents the visual world. That structure, the tectum, can elicit not just orienting movements but also escape movements. And they're different kinds of pathways. The pretectal does similar things. Non-mammals it's a larger structure. Relatively smaller in mammals. We know in mammals it plays a role in protective responses. It controls contraction of the pupil to bright light.

We know, if there's a rapidly approaching object, it can elicit avoidance movements. We also know in some animals where it's been studied well, and there's some evidence in certain mammals, that the animal can avoid stationary barriers with mechanisms in the pretectum.

So that kind of orienting it seems to be important for. But its role in simple orienting towards novel objects in the visual field, we know much less about it because the studies have focused on the tectum. We talk about the visual grasp reflex, so just like we reach out and grasp something with our hands, we grasp something with our fovea, by turning our eyes to directly look at an object in the visual field. And the use of electrical stimulation, as well as brain lesions, have identified these two distinct outputs. One for escape, and that involves an uncrossed, descending pathway from the tectum. And then the cross, tectal's final track, that moves the head and eyes towards the object. And we talked a little bit about that already. I'm mentioning it again now that we're talking about motor system.

Now, a little more about that third type of movement, of grasping. Which can be with the mouth or with the limbs. So the animal approaches something. He orients to it.

And he can grasp it either directly with this mouth or by reaching, and oral grasping

6 is part of the orienting movement in many animals. They move their head towards something. They often move towards it at the same time. And then, how do they actually grasp it orally? There are some connections from the tectum to the fifth nerve nucleus to control the jaws. But the major control of that movement is not through the visual system, but through the .

So, for example, a little rodent is bringing the fluid or whatever he's turning towards into his whisker field. And then the somatosensory stimulation triggers the movement. That's true for the cat as well, and probably for many other animals. But animals that use a less somatic sensation, like a fish, it's more under the control of vision.

So even after neocortical expansion, these mechanisms remain important. The higher controls are there, but both spinal and hindbrain mechanisms are controlling these orienting and the grasping movements.

There are also reflex types of controls, involving somatic sensation. For example, in a human baby, before he is really able to control grasping by vision, his endbrain is very immature. You can actually elicit grasping movements simply by touching, for example, the back of the hand. And he will turn the hand and grasp. And that's partly done by the tactal reflexes, but also by proprioceptor reflexes. For example, when his arm is pulled up, he will also grasp as if he's attempting to hold on to something that causing his arm to stretch. So we know there are many levels of control of these types of movements. And I'm only going to talk about the midbrain mechanisms here.

The structure in the midbrain that's most important is the . It's an interesting nucleus when we do comparative studies, because it's not there at all in those very primitive vertebrates, the hagfish and sea lampreys. These are the primitive jawless vertebrates. Very few animals in that group that haven't gone extinct. But they are present in more advanced fish, and in frogs. And it's pretty prominent in the reptiles, the birds and the mammals. Because I emphasize the role of the red nucleus in grasping, many people have asked me-- because I used to

7 leave this out-- is there a red nucleus all in animals that don't have limbs and can't grasp? And the answer is, many of them, yes. And we know a lot less about its role in these animals.

A little more about comparisons. If you just take the red nucleus in the midbrain, seen at the bottom here, we see it's got two major components. That descending projection that we know is important in controlling the muscles of the hands and feet, comes from this large-celled component, which is the caudal component. So I've indicated that by the blue dots here. And then the [UNINTELLIGIBLE] part, of course, is in yellow. It just has smaller cells. And I've colored for you here.

Note the change in different animals. Here, in carnivores, like the cat, the small cell red nucleus is pretty small. Most of it's the large cell red nucleus, giving rise to the rubrospinal spinal tract. But in monkeys it's like half of it is the small celled nucleus.

And in apes and humans the small celled nucleus is by far the dominant. That small celled component does have connections to within the red nucleus, but it has important connections that ascend to the thalamus.

Which means providing information to the . Because in apes and humans, the motor cortex control has become the dominant means of controlling this kind of movement.

One other thing about the rubrospinal projection, in another kind of comparative study and this is described there in the [? Streeter ?] book but I'll go over it right now, was a study of those neurons in the red nucleus that project to the spinal cord.

We know they project mainly to the enlargements that control the limbs, because they're controlling this kind of movement.

Look at the lower right here initially. And then let me describe the experiment. They used retrograde tracers, so here they've injected a tracer into the lumbar cord. It's a pretty big injection, so they get all the neurons in one region of the lumbar cord. And then they look up in the red nucleus, and they find neurons that project to the lumbar cord. By that experimental means. And they find them distributed through one part of the red nucleus. 8 Then they do a similar experiment, and sometimes they do this with two different retrograde tracers in the same animal. They inject the that controls the upper lips. Do the same experiment, and they find where those neurons are located. And we see that in the cat they're located in a different part of the red nucleus. There was one neuron that actually projected to both cervical and lumbar enlargements.

Similar experiments were done on the rat, and here we see a greater intermixing.

The red nucleus has not become so neatly divided into one part controlling upper limbs and one part controlling lower limbs. And there's more of those neurons that projected [UNINTELLIGIBLE].

If we look at the opossum, it's even more disorganized. Even though the very same experiment was done in all these animals. Same methods, same experiment. And that kind of change, we see in a number of different systems when we do comparative studies. And the usual differences are like this. That in more recently evolved animals, there's been a great parcelation, we call it. Separation of different functional regions.

To talk about somatic motor control, we'll talk about how the motor neurons in the spinal cord are organized. First just let's recall that the somatic motor neurons are just one type of motor system. We have the autonomic systems, the neuroendocrine systems. And this is the way they were diagrammed once. Here's the somatic motor neuron for the synaptic connection to muscle cells.

Here's the autonomic system, with preganglionic motor neurons connected to a ganglion cell. It's in the peripheral nervous system, which then connects to motor neurons of the autonomic system. Parasympathetic or sympathetic. And then we have the neuroendocrine system, where the neurons in the CNS secrete in the bloodstream.

These are three major kinds of systems. This is Swanson's diagram of the three motor systems, where he shows some further subdivisions. He shows that there's

9 really both small celled and large celled components of the endocrine secretory system. Here's the two components of the autonomic nervous system. It's the different positions of the ganglia. And then here's the somatic system.

So now what I want to talk about is this system and how it's organized. He just shows it as one system here.

First of all, where are the motor neurons located? This is Swanson's diagram, and we've seen this in the [? Schmubrain ?] diagrams too. The motor neurons are located in the ventral horn of the spinal cord. Here's the cervical enlargement. The of the cord, where there's more motor neurons controlling the hands and feet.

And then we get up into the hindbrain, we have these motor neuron groups that send their axons out through the various , which are numbered here.

And there the motor neurons are not in a continuous column all through the hindbrain and midbrain, but they're found in these separate little nuclei or cell groups. Those are the motor neurons of the somatic system. He's left out the motor neurons of the preganglionic motor neurons of the autonomic system. And he's left out the endocrine system. Just the somatic system. And he's named here the various cranial nerve and components of these groups of motor neurons.

So now I'm going to show the spinal cord at one of the enlargements, how the are organized there. And how the descending connections from the brain relate to those motor neurons. Which is where I was supposed to start today, but--

First of all if you look at the spinal cord at the cervical level, there's been-- some medical school texts like to show the organization of motor neurons there in the ventral horn at the cervical enlargement this way. What this is supposed to show is that the motor neurons that control the axial muscles, nearest the body axis, are located more immediately. And the more neurons controlling the most distal muscles are located most laterally in the core. The muscles controlling the [UNINTELLIGIBLE] muscles of the hips and shoulders are in between. 10 And this comes from a detailed study by a Dutch neuroanatomist Henricus Kuypers, who did a wonderful study, published in 1968, of the organization of the somatic motor system. He included [UNINTELLIGIBLE] they did neuroanatomical studies, and Kuypers had been doing a number of those before this, and then they did a functional study using lesion method. And I'm going to go through what they did.

So here's, then, the picture of the cord. So here you see just a little picture of motor neurons from medial to lateral. And he's showing that the distal muscles of the limbs are located laterally. Proximal muscles are enervated by the medial motor neurons. And he also shows that the interneurons here, which he shows only on the left side here, the interneurons have the similar [? enrangement. ?] That is, the lateral interneurons are connecting to the lateral motor neurons. So the lateral interneurons are also more concerned with distal muscles, and the medial interneurons are concerned with the axial and girdal muscles.

And notice here that he shows a cell, an here, that connects to both sides. Only the interneurons concerned with the axial muscles do that. It tends to be a bilateral system. And just remember the term girdle here refers to control of the shoulders and hips.

So there's that picture, down below. And above it he's showing pictures from studies summarizing studies of the descending projections from the brain. First of all, on the left there, he's showing all of the various studies of . He wants to show where, if you just look at all the corticospinal tract axons, where do they terminate at one of the cord enlargements?

And he finds out that they terminate throughout the interneuronal pool on both sides. But on the opposite side, only to that medial part. So apparently there's some bilateral projection controlling the axiom muscles,e but not the more distal muscles.

And we'll see a functional reason for that in a minute.

Notice also that they go directly into the groups of motor neurons. Now, of course, those groups include interneurons too, so that doesn't prove that they connect

11 directly with motor neurons. But separate studies have shown that they indeed do.

There are direct connections to motor neurons, especially in the higher animals.

Then they separate. With [? Lorenz ?], he did study separating pathways coming from the lateral brainstem, the lateral hindbrain primarily. Also the midbrain. They travel laterally through the hindbrain, laterally through the cord. They come in through these lateral columns. And they project in the dorsolateral part of the interneuronal pool primarily, very few go to this medial area.

The central medial brainstem pathways that includes the vestibulospinal, tectospinal and some reticulospinal axons, they have a contrasting pattern. They go to this ventral medial position, and they also tend to go to the opposite side also. The most medial part of the opposite side.

So the two systems are rather different. Just by separating the lateral brainstem and the media brainstem pathways. This lateral brainstem pathway, much of it comes from the nucleus [UNINTELLIGIBLE], that red nucleus in the midbrain. But, others it is joined by cells in the lateral of the hindbrain as well.

All right. Now, I'll enlarge these. I want you to see the overview first here. First I'm going to show you that the corticospinal projections, which I show in these diagrams, using a monkey brain here, and here the embryonic brain that we've been using, I'm showing the corticospinal projections. And I've separated the systems for controlling the distal muscles of the limbs, like the hands, shown in the solid line. And the axial muscles. They come from different parts of the motor cortex here.

And then I separate the lateral brainstem pathways and the medial brainstem pathways, showing where they originate and how they travel. So first, the corticospinal. We see the body has a topographic representation in the motor cortex. What is the motor cortex, again? How do we define it? It's the cortex where we can elicit movements by electrical stimulation with the lowest current. The tiniest currents. So with tiny currents through our electrode, that can't elicit movement from any other parts of the cortex, we can elicit movements by stimulating the motor 12 cortex. And that's how it was discovered. That's how it was defined initially.

It's not that it's the only cortical area where you can elicit movements. You can elicit movementts from many different cortical areas. For example, from the visual cortex, or the somatosensory cortex. You can certainly elicit movements from those areas.

But the motor cortex where you can do it is where you can do it with the tiniest currents. That's because there are large neurons there in the fifth layer that send their axons directly to the cord and some of them even directly to motor neurons.

And we can divide it. We find the larger areas that represent the distal muscles, but we also find the rest of the body muscles represented there. And I've shown those in the dashed lines.

So the lateral brainstem pathways, I show here coming from the red nucleus in the midbrain. And it's a cross-projection, crossed like this. It's joined by some neurons in the reticular formation of the hindbrain. And they project primarily-- not exclusively, but largely to the enlargements. The cervical enlargement and the lumbar enlargement.

And here in the hindbrain, here's the cross-section in the midbrain. And here's where they travel through the hindbrain, in this lateral position. The corticospinal axons are down here. There they are coming through the midbrain through the cerebral peduncles in the midbrain. There they are in the pyramidal tracts at the base of the hindbrain.

The medial brainstem pathways are coming from the optic tectum, up here in the midbrain. They only go as far as the cervical cord. They're coming from vestibular nuclei there, in the rostral hindbrain. And many neurons in the medial hindbrain reticular formation contribute axons also to those descending pathways. And they travel medially through the cord. Here they are in the hindbrain, being joined by axons of these medial neurons. They travel in that menial position through the hindbrain. They travel in the ventromedial columns of the spinal cord. And they terminate all the way up and down the cord. Not just at the enlargements. And they tend to terminate on both sides, more on the same side than the other side. 13 So here was what [? Lorenz ?] and Kuypers did. They began by eliminating the corticospinal projections. Why did they do that first? Well, they tried just eliminating the descending hindbrain, the pathways that come through the hindbrain. The lateral pathways and the medial pathways. And they found that they didn't get much of an effect as long as the corticospinal tract was still there.

So they reasoned that the corticospinal tract had become so dominant in these monkeys that they were studying, that the only way they were going to see the role of these other pathways was if they eliminated the corticospinal tract axons first. So they did what we call a pyramidotomy. They cut the pyramidal tracts in the hindbrain. And of course they got some [? diascescus ?] effects. Animals got weak.

They had a little trouble moving for a while, but they recovered. So they waited for some recovery to occur.

They did get some residual effects. It's not that the corticospinal tract isn't doing anything new. The movements were a little slower, they were a little weaker, and the monkey couldn't do this. Couldn't do that anymore. He could only do that. So the monkeys could still function pretty well. But they lacked some of the finesse of the animals with corticospinal tracts.

So then they worked with those monkeys that had the pyramidotomy. And then they did either this leson or that lesion. They eliminated one or the other of those pathways from the hindbrain. Now, remember the medial pathways tend to go to both sides. And if they made that lesion on just one side, they didn't get much of an effect. So that lesion, they had to get both sides. The lateral pathways tend to stay on one side, so that one they could usually do just on one side. And they could compare the two hands.

So here's their lesions. First pyramidotomy, and they were doing it up there in the hindbrain. When the pyramidal track travels right along the base of the hindbrain. I've done this legion also in hamsters to be able to compare with the monkey results.

14 Here you see the lesion where it was in the hindbrain, and it goes across the midline, it gets both sides. Both pyramidal tracts.

And then they allowed recovery from that lesion. Then they added the second lesion. And what they did is expose the base of the hindbrain again. Same way they had done for the pyramidal tract lesion. But now they inserted a knife that went up along the midline. But left all the lateral pathways intact. They cut all those medial traveling axons, as I show here. And they observed what happened. Other animals, they added a lesion of the lateral pathways making it at the hindbrain level. Here's a cross-section of the hindbrain. They went in there with an electrode and burned a lesion, burned an area out, eliminating the and many of those other axons.

So that was the logic they were following. So, what happened? With the pyramidotomy, loss of speed and strength and loss of control of the digits used one at a time. They had a little food board, with little cups. Large cups, small cups, with tiny bits of food in the small ones and larger bits of food in the large cups. And they just looked at what the monkey could do.

I have a film of this, I wish we had time to show the film. It's a very nice film and you see these defects in the monkey. But the monkey with the pyramidal tract lesion could get all the larger bits of food and the larger cups out using his whole hand. But he couldn't get the little bits that he needed to his oppositional thumb and the single fingers. So that remained lost with the pyramidal tract lesion.

So now those pyramidotomized monkeys, some of them had a destruction of the medial pathways. When you first see these monkeys, it looks really bad. The monkey's just lying there. He can't even right himself. So in fact, it took them about some of them up to 40 days before they could right themselves. How could they ever right themselves? They're missing all the pathways from the vestibular nuclei. Well, they have somatosensory inputs coming in through their limbs, through their touch system. And they gradually reacquired the kind of movement that those inputs caused. And they regained the ability to right themselves. But it shows the

15 dominance of the vestibular system for this kind of movement.

They didn't really have the normal corrective movements when they would be falling, as you expect without the vestibular system. They walked in a really odd way. They could recover pretty good walking, although it was not good at all at the first. But they didn't seem to be able to orient normally. They would be walking towards some food there, and they would wander off to the side. They seemed very unable to direct their movements towards a goal. It was very dramatic, these effects.

So did they seem really helpless? Yes. But, you strap them in a chair where they don't have to control their axial muscles. You strap them in a chair and give them use of their hands. Now, they had a little trouble extending. But if you brought the food close enough, they could reach out and they could make this movement and they could pick up the food. So they definitely had some movement control. They couldn't control their axial muscles as well, but they could control those distal muscles. They had those pathways. As the anatomical studies had predicted, they should still have, after that lesion. So distal control was much better than axial control.

If they did the lateral brainstem pathway lesion instead, and they did this only on one side, now it was very interesting. They sat them, strapped them in the chair. One of the hands could reach and grasp quite readily. The other hand would start to reach but couldn't grasp the object.

And it seemed very odd because if you let the monkey go, let him run around the lab, he could climb the cage using both hands, as long as he was doing locomotive movements and whole body movements, they called them, he could control the hands. But you put him in a chair and you're asking him to just control that one hand in a grasping movement, he couldn't do it.

That tells you something about the nature of paralysis. You can be paralyzed for one use of the muscles in one situation, and not in other situations. It depends on the movement and how it's organized in the central nervous system. 16 I just want to mention here that the people that have lost their tetraplegics, sometimes we say quadriplegics, when the like to combine the Latin and the Greek. I like the one just from the Greek, tetraplegic, complete losing ability to move all four limbs. If those people, you ask them to just think about doing something, you do activate parts of the motor cortex. And here they're showing, when they asked them to move their lips, of course the lips weren't moving, but they were imagining moving their lips. They felt they were moving their lips. They activated that part of the motor cortex.

Similarly, for one hand or the other hand, one arm and the other arm. So they still have an organized motor cortex. So we know if we had a way to get those long pathways reconnected, or are some other way to use that activity of the brain, we should be able to get those people to move again, and various people working on new prosthetic devices are trying to

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