Higher Cortical Functions

Basic and Clinical Neurosciences

28th Annual Postgraduate Review Course December 3, 2005, through March 11, 2006

Higher Cortical Functions Randolph S. Marshall, MD, MS March 4, 2006 Chapter 1: Introduction Randolph Marshall: Okay, so we get to move on with our discussion of higher cerebral function. You heard about language function and dysfunction from Dr Lazar. I work with Dr Lazar in the cerebral localization lab in the stroke division in the neurology department. And my research interests include some behavioral aspects of stroke, but I’m particularly interested in stroke recovery and how the brain reorganizes after injury. But today I’m going to give the lecture about dyspraxia and hemineglect, so we’ll extend the information you’ve already heard from left hemisphere function; we’ll discuss dyspraxia, which can be left and right hemisphere; and then hemineglect, which is predominantly dysfunction of the right hemisphere, as we’ll see. The information that you’ll get will appear I’m sure on some tests or elements in the boards eventually, but it also makes great cocktail party conversation, and you’ll see from some of the videos that I have that a picture is worth a thousand words in these cases. Chapter 2: Defining Dyspraxia So let me first begin by defining dyspraxia. It’s been very ably described in text-

http://neuroscienceupdate.cumc.columbia.edu

1

Basic and Clinical Neurosciences

28th Annual Postgraduate Review Course December 3, 2005, through March 11, 2006

books and the literature, and so I’m going to use this one here. The basic concept is an impairment in the execution of a motor act, learned or imitated, in the absence of primary weakness, sensory loss, or incoordination. Testing those elements individually, patient has no hemiparesis, has no sensory loss, and has no incoordination, and yet is unable to do motor acts, simple or complex. The dyspraxia types again is divided variably in the literature, but I’m going to use this nomenclature now—ideomotor apraxia or dyspraxia is interchangeable, is considered the inability to integrate these basic sensory motor elements to achieve a simple motor goal. The so-called limb-kinetic apraxia is basically the inability to carry out those motor acts with the hands—for example, using or imitating the use of scissors. Bucco-facial apraxia, I don’t know whether Dr Lazar showed an example of speech dyspraxia, but that’s an example where the individual elements . . . there’s no loss of strength, sensory loss, or dysarthria per se, but targeting the articulatory output for speech and language is a form of dyspraxia. And walking likewise, no weakness, no particular ataxia, but inability to walk properly is seen certainly in the rehab field. Ideational apraxia, and so the basic idea, ideomotor apraxia—referring to more directed goal-simple motor acts—ideational apraxia, the inability to combine those simple motor elements to achieve a complex or sequential motor act. It’s often seen in the later stages of Alzheimer’s disease or other dementias. But I’ll show you some examples where focal brain injury can produce this effect as well. An example would be something like a more complex act, like dressing or cooking, where those sequential elements, getting things in the right order, combining the elements to produce the overall goal of a more complex motor act is the ideational apraxia. Then somewhat separate from that is constructional apraxia, which has to do with the ability to produce a mental image, either copying or usually from a mental image of an object to produce it on paper. For example, a patient with hemineglect may have a type of constructional apraxia whereby the left side of the objects are not recreated correctly, a missing hand, a missing eyebrow, a difference on the left versus the right; or a generalized dyspraxia where there’s sort of some rough resemblance of the object, you know that the patient knows what

http://neuroscienceupdate.cumc.columbia.edu

2

Basic and Clinical Neurosciences

28th Annual Postgraduate Review Course December 3, 2005, through March 11, 2006

they’re trying to draw, but they are so disordered, and these are patients who have no hemiparesis, this is not a motor problem per se, but cannot create the image of the object on paper. A typical test for neglect or apraxia is this ray complex figure, which is copied or then recreated for visual-spatial memory, but in particular a ray copy like this may be disordered, and you can see how the elements are not created in the correct proportion, and there are errors made with lines and so on. This is interesting because this is a patient with a focal brain injury, a hypoperfusion syndrome on the right. He also had an AVM [arteriovenous malformations]. With a right hemisphere dysfunction he produced this ray figure, and a surgery which revascularized the right hemisphere allowed the recovery of that dyspraxia. So localization of dyspraxia, you can see it with dominant frontal or parietal lobe, or you can see bifrontal injury producing this syndrome. Often when it’s bilateral or dominant you’ll have both limbs involved. It can be associated with an aphasia, because of course the aphasia is predominantly from injury of the left hemisphere; and sometimes it can be a little difficult to dissociate the dyspraxia from the aphasia, because you ask a patient to, for example, pantomime scissors. If they don’t know what you’re asking them to do, if there’s comprehension impairment, you may not be able to identify or dissociate the dyspraxic component from the aphasic component. This is mitigated by having them just imitate, because not requiring a language command to produce the act, imitating or giving the patient an object you can see that appear even with aphasia. Then there’s the very interesting syndrome, and I’m going to show you some of this of a disconnection, where the corpus callosum is involved, and you get an apraxia of the nondominant hand only. We’ll review the anatomy of that after I show you an example of that. Chapter 3: Cases of Dyspraxia So, let’s go to the videotape. This is a patient who has one of these disconnection syndromes. What you’re going to see, he actually has a right hemiparesis so that he’s weak in this right hand, but you’ll watch as I discuss using the move-

http://neuroscienceupdate.cumc.columbia.edu

3

Basic and Clinical Neurosciences

28th Annual Postgraduate Review Course December 3, 2005, through March 11, 2006

ment of the left hand. Now often with ideomotor dyspraxia you can get a dissociation between attempting to do the act, or imitating, pantomiming the motor act, versus using the object itself. In this case you’ll see that there’s a dissociation; and I have another example later on, where the thought process of getting the act from the brain to the hand is impaired, and yet when you have the cue of the real object, you can sometimes see an overcoming of the dyspraxia. [Video] “Okay. And you were telling me yesterday that sometimes you could get your hand to do what you wanted, and other times not. Is that still happening today? Can you, for example, can you show me how you would put on your glasses, just pretending how you would put on?” “All right. You can’t show me how you would put on.” “No.” “Okay. Now let me just give you your glasses here, okay? And I’m going to have you read something, okay? Let’s get out what you have to read. You showed me . . . you looked at some pictures earlier, okay. Now before all this, your hand was working okay, right, the left hand?” “It’s working now.” “Yeah, okay, just put it right on. Okay. Good.” So you saw that trying to get that idea of the motor act to his hand without the real object, he failed, and yet you put the object in his hand and there it is, you know, the sensory cues, the automatic action actually just comes out. This is a sagittal view of an MRI, here’s the brainstem down here, where the medial portion of the frontal and parietal lobe is shown here, and of course above the ventricles is the corpus callosum. You can see on this T2 image that he has infarction of the anterior cingulate and some portion of the corpus callosum. And now if I could have the lights up, I’m just going to draw this on the board. I know it’s old fashioned, but what the heck? So let’s say this is the brain here, and this is the left side and the right side, and corpus callosum of course is connecting both sides of the brain. Here is the Wernicke’s area, so that’s the left. Here’s the right hand, forgive my rendition here, and here’s the left hand. Now to move the right hand we’re going to use, let’s just call this motor area M1, which of course crosses down in the decussation of the pyramid, so it has nothing with the corpus callosum. And so movement of the right hand, although he’s got a hemiparesis, he would normally be able to move fine. Movement of the left hand,

http://neuroscienceupdate.cumc.columbia.edu

4

Basic and Clinical Neurosciences

28th Annual Postgraduate Review Course December 3, 2005, through March 11, 2006

though, is going to also require the downward projecting cortical spinal tracks across the decussation of the pyramids in moving the left hand. But if the information has to get to the motor system to instruct it, and you have a lesion in the corpus callosum, and you can’t get the information across, you can still move the hand just fine but you can’t get the information across when you’re instructing it to do so. However, no problem just sending the information up and moving the right hand, because the intrahemispheric connections are still intact. That’s how this disconnection syndrome works. It’s pretty rare, but it’s fun to see it, and it tells you something about neuroanatomy when it happens. Let’s move on to another person. She has actually both an ideomotor apraxia, which I’m going to demonstrate here, and then I’ll show you her ideational apraxia. [Video] The instruction was to pretend she’s using scissors. “Now try. Pretend you’re using scissors.” This was a former clerk at a hospital, so she should know how to use scissors, right? “A piece of paper.” She has this ideomotor dyspraxia which is present in both hands and is present for both the imitated or the idea of the act, as well as use of the real object. Now she also has ideational apraxia, and I’ll just demonstrate that here. [Video] “Just pretend, okay.” “What about your . . . ?” So no aphasia, clearly able to describe. “Actually I have a coat for you. Try to put it on, okay? I know, I know. You can do it. No problem.” “All right.” “Here you go.” “But I’m going wrong. For some reason . . .” “For some reason?” “Yup. Okay? Okay.” “I’ll bet you did.” She actually was admitted for what was interpreted as confusion because she was not able to get dressed in the morning, that was her presentation. No headache, no weakness, no sensory loss, no discoordination—was putting her underwear over her pants, couldn’t get her shirt on properly. And it’s now a few days later, so it’s recovered to a certain degree, but you saw that she had difficulty figuring out the order of things, the direction of things, the visual-spatial orientation, and so on. Now she ended up having a bifrontal lesion, so emboli that

http://neuroscienceupdate.cumc.columbia.edu

5

Basic and Clinical Neurosciences

28th Annual Postgraduate Review Course December 3, 2005, through March 11, 2006

went to both frontal lobes here. This is an axial flare image of an MRI up in the upper regions. This is left, this is right, and so you can see the two lesions here, in the posterior frontal region, frontal parietal on the left. And that produced this combined ideomotor and ideation apraxia. I’ve got one more, which is really bizarre. This guy has the inability . . . he’s also got this disconnection syndrome, and he happens to also have a right hemiparesis. You’ll see he’s able to use his right hand, it’s weak but you’ll see how he’s able to use it. But he has, when he attempts to use his left hand with an instruction—so a language component—he defaults to this bizarre motor program which puts his arm up over his head. He was normal before, I forget what his job was, but he was a normal guy with otherwise no mental status problems. So just watch this. The tape is a little shaky so I apologize for that, but we’ll see. [Video] So completely normal coordinated movement of the left hand when it’s doing what it needs to do, balancing a peach on a fork to get it to his mouth, and yet either when he was instructed to do a motor act, like hold up two fingers, or he was instructing himself, which probably what was happening just before that, the fork, to get his hand to the fork with a verbal instruction presumably in his head to get it, he couldn’t do it. And yet when given the fork, and this is another example of that dissociation between using the real object and having to use a verbal command to accomplish the act. Chapter 4: Hemineglect I’m going to move on to hemineglect here. Hemineglect also is somewhat of an unusual syndrome seen mostly in the acute phases of stroke anyway. You can see it in other examples of brain injury such as tumor, head trauma, but generally it occurs in the acute phases. These are manifestations of hemineglect. Its core element is an inattention to one side of space, and usually with a right hemisphere lesion, it’s an inability to attend leftward. You can see it as unilateral extinction when giving the patient double simultaneous stimuli, either in the visu-

http://neuroscienceupdate.cumc.columbia.edu

6

Basic and Clinical Neurosciences

28th Annual Postgraduate Review Course December 3, 2005, through March 11, 2006

al or tactile mode, and asymmetrical orienting response such that instead of orienting to the midline they tend to preferentially orient to the right rather than to the left, asymmetrical drawing or copying like that picture I showed you at the first slide of the constructional apraxia. Motor neglect is this unilateral limb hypokinesia, where if you ask the patients to raise both hands, for example, they may just raise the right hand; yet on encouragement and confrontational testing their motor function is actually just fine on the left side. Anosognosia which you probably know is the unawareness of the deficit, of a deficit. Patients come into the emergency room, for example, with left-sided weakness, plegia, inability to walk because of that or move their hand, and you ask them what the problem is. They say something like, “I just can’t walk.” And you say, “Why is that?” They say, “I’m just sort of generally weak,” unawareness that it’s the whole left side of the body that’s impaired. A kind of a submanifestation of that is asomatognosia, which is a striking syndrome where the patient does not recognize the left side of their body as their own. You can hold their left hand in front of them and say, “Whose hand is this?” and they say, “It’s your hand” or “It’s not mine” or there was one example of a senior colleague of mine [who] said a patient reported to him that that was the hand of a Zulu warrior. Now what it was doing in bed with him, he wasn’t sure. In order to test for hemineglect we have some standardized testing which allows us to quantify and characterize the hemineglect. That picture description, like the cookie theft picture that was used for the aphasia that Dr Lazar mentioned, can be used to look at asymmetrical orientation, extinction to visual or tactile stimuli were mentioned already, having the patient identify one or both fingers held up in front of them; so when the dissociation being, of course, when you hold one finger up and say, if you’re the patient, “Which finger is moving?” they could identify the right side, they can identify the left side; but when both are given simultaneously they only identify the right as being moved, likewise in the tactile mode, right-left, extinguishing the left one. Spontaneous drawing, as I showed before. This motor delay or impersistence . . . so asking patients to raise both hands, then if only one goes up, the left delayed, that’s a manifestation of motor neglect. Then the more quantitative, which we’ve really tried to standardize here at Columbia for the residents, is to use line bisection and target cancellation. These

http://neuroscienceupdate.cumc.columbia.edu

7

Basic and Clinical Neurosciences

28th Annual Postgraduate Review Course December 3, 2005, through March 11, 2006

are excellent tests because they’re simple to administer, they’re quick to administer, they’re quantitative, and you can follow the progress of the patient over time. This is that cookie-theft picture that was used earlier. A patient with hemineglect typically you’ll hold this card in front of them and ask them to describe what’s in the picture and they say something like, “Well I see a curtain and some dishes.” And you say, “What else is going on?” “Oh, I see, I’m sorry, yes, there’s water overflowing the sink here.” “Is there anyone in the picture?” “Oh yes, I see, oh, I’m sorry, yes, there’s a woman drying a dish there.” “What else is going on in the picture?” “Oh, I’m sorry, yes, there’s an open window and another curtain.” “Anyone else in the picture?” “No, I just see the one person. Oh yeah, I’m sorry, yes, this is a cabinet down here,” and so on. So always orienting toward the right side of the picture and never moving leftward. This is a presentation of a stimulus on a computer screen, but the classic test is just horizontal lines, asking the patient to bisect the line, and those with certain aspects of hemineglect will bisect the line to the right of the true midpoint, indicating that they are perceiving the line asymmetrically with attention more to the right side than the left. I’ll show you a little more of that and how we can ferret that out. These manifestations of hemineglect are often described in a battery. If you look in the literature on hemineglect patients will be said to have hemineglect yes or no, based on a battery of tests which may include target cancellation and line bisection tests. However, this is a paper we published way back, ancient history now, but we showed a dissociation between these two basic types of hemineglect testing. One set of patients was relatively normal on their line bisection, these were lines given sequentially on individual pieces of paper, and the bisections were done fairly accurately. And yet on the target cancellation test you can see—the task is to circle all the A’s on the paper—and only the ones on the far right side of the page were identified. That was in contrast to another set of patients who did fairly well on their cancellation test, and yet were markedly asymmetrical on their line bisections.

http://neuroscienceupdate.cumc.columbia.edu

8

Basic and Clinical Neurosciences

28th Annual Postgraduate Review Course December 3, 2005, through March 11, 2006

Now how did that happen? It turned out that there was a dissociation anatomically between these two sets of [patients, and this is somewhat] analogous to the aphasia syndrome where posterior lesions of the left hemisphere produce a sensory aphasia, and anterior produce a motor aphasia. Similarly, you can think about these two aspects of hemineglect in terms of motor and sensory, such that those who had abnormal cancellation with normal line bisection tended to be those who had right—and this is anatomical orientation, right dorsal lateral prefrontal predominantly. This is a template of overlapped lesions of patients who had a given syndrome subtracting out all the lesions of those who didn’t have the syndrome. The one on the top was those who had the cancellation with normal line bisection, and these were patients down here in the temporal parietal occipital junction who had line bisection abnormality. So that perceptual type of neglect, and I’m going to go into that in a little more detail in a moment, tended to have the posterior lesions. You can think of this as a motor or exploratory inability to move leftward on a cancellation target task. Those are also patients who tend, not surprisingly, to have hemiparesis, because they have frontal lesions. They tend to have gaze deviation, or at least gaze preference to the right side, because of the proximity to the frontal eye fields. But they can dissociate in having normal perceptual abilities in a line bisection task. Chapter 5: Functional Imaging of Hemineglect Some more recent work, this is by Corbetta, et al, just published in Nature Neuroscience last year, in which they did a functional imaging study [an fMRI study] of patients in acute and chronic neglect. These were patients with right hemisphere lesions. The task was the Posner task where you have a cue followed by a target stimulus, so the arrow goes right or left; and then you get either a valid target, which is the stimulus appears where it’s supposed when the arrow’s pointing that way, or an invalid cue. And so you look at the degree to which the orienting response helps the accuracy on the task. Normally, these are control subjects, activate basically bilaterally, left hemisphere and right hemisphere, predominantly parietal regions and the dorsal lateral frontal on the left side. In the neglect patients in the acute phase they had lesions here, but not

http://neuroscienceupdate.cumc.columbia.edu

9

Basic and Clinical Neurosciences

28th Annual Postgraduate Review Course December 3, 2005, through March 11, 2006

only did they have no activity of course where the stroke was, but on that task had no activity in these critical other frontal and temporal parietal regions. On recovery later on, so a few months later, they showed this reactivation in the right hemisphere and normal performance then on that task, also a reaccumulation of some of the lost activity on the left hemisphere. So correct and accurate attentional tasks require bilateral activation and a balance between the right and left hemisphere, and if the right hemisphere is absent that looks like that, from the lesion and then beyond the activation in the right hemisphere absent produces, this was more of the orientation type of syndrome, that would be commensurate with the target cancellation task. Hemineglect can also occur with a thalamic lesion, and some subcortical lesions, particularly if they’re bigger—head of caudate and larger thalamic lesions—and the idea here is that it’s not just the thalamus, but its connections to the cortex. If you look at a SPECT scan you can see an asymmetry in the temporal lobes, and an asymmetry in the posterior parietal lobes here, showing hypoperfusion in the right hemisphere associated with this deep lesion in the thalamus. This patient had hemineglect. In a small series we looked at patients who had these remote SPECT effects. The ones who did, so for example this patient on CAT scan— anterior limb of internal capsule and centrum semiovale had this hypopefusion on SPECT and had hemineglect. This patient, the one I just showed you with the thalamic hemorrhage, had that temporal and posterior parietal hypoperfusion and left hemineglect. The left sensory motor, but no neglect was present in this patient with an equally large hemorrhage, but no hypoperfusion. Then a patient with a cortical infarct had hemineglect, and had frontal, parietal, temporal, and occipital hypoperfusion. The idea of that SPECT scan is that not so much that the blood flow is down from a loss of blood flow with larger artery disease, but this idea of diaschisis whereby a lesion in one location metabolically suppresses an anatomically connected but remote lesion. And so the manifestation of hemineglect probably is a cortical one, but can be manifested from the lesion in a deep location.

http://neuroscienceupdate.cumc.columbia.edu

10

Basic and Clinical Neurosciences

28th Annual Postgraduate Review Course December 3, 2005, through March 11, 2006

Chapter 6: Crossover Effect I want to just discuss one last syndrome in hemineglect, because it was a thorn in the side of people studying this syndrome for many years. And that was this crossover effect. It turns out if you present patients with varying lengths of line, patients with hemineglect, the longer the line the further to the right they tend to bisect the line, so the further abnormal away from the true midpoint they tend to bisect the line. Percentage-wise about the same, but as the line gets longer, it’s further to the right. If you present shorter and shorter lines there reaches a point, it seems, that they actually bisect the lines—the short lines, to the left, to the wrong side of the true midpoint. Now why should that happen? It really doesn’t make sense from traditional hemineglect theory that the inability to look leftward—to attend to space on the left side—is impaired. Some people thought, well maybe you’re getting the line short enough that you’re within foveal vision, and so you can encompass the whole line grasping it with a single visual angle; but that didn’t really match, it didn’t make sense that that mere fact would alter the performance. In fact, what we did was look at the lines first individually, and then in combination. That was done this way, we first presented these line lengths individually to patients with hemineglect. The shorter one did have slightly less deviation to the right, but basically each of these—4, 6, 9, 12 centimeter lines—averaged about 17% deviation to the right, no matter what length line, if it was presented individually it was bisected to the same degree to the right. However, if we took a 6 centimeter line, for example, and gave the patient that line to bisect, with 6 alone would be the average of this 17% bisected to the right. If you then mixed the set of 6 centimeter lines with longer lines, 9 or 12 centimeter lines, the performance on the 6 centimeter line shifted to the left. So that now if you mixed it in, the 6 centimeter lines were being bisected at 5 to 10 degrees. If you gave 6 and then added in shorter lines, the performance on the 6 centimeter line shifted to the right side. We then carried this further and showed that in several of these patients—so 6 centimeter line with 3 deviated to the right—and we could in some cases add in a line that would actually make the patients on the index line bisect to the opposite hemisphere. This was one either on manual bisection or presenting the lines on a computer screen that are bisected and dividing the line into two colors— which one is longer—essentially the same type of line bisection assessment but http://neuroscienceupdate.cumc.columbia.edu

11

Basic and Clinical Neurosciences

28th Annual Postgraduate Review Course December 3, 2005, through March 11, 2006

without the motor component. In this case 6 alone, adding in a longer one shifted the line leftward, with a 4 centimeter line and adding in a longer one shifted the patient across the midline. So what was happening here? Well, the working model of hemineglect, there have been a variety of theories about what’s happening here, dating back to the ‘70s and then the ‘80s was this idea of attentional asymmetry, Kinsbourne and then Heilman and the Denoble described this, and then in the ‘80s and ‘90s that was additionally discussed. The role of the parietal lobes was of course first described by Brain and Denny-Brown and Critchley back in the ‘40s and ‘50s— that the role of the parietal lobe was to integrate sensory information, and if you knocked out the parietal lobe you wouldn’t be able to integrate sensory information from both sides of space. The motor neglect idea was put out in the late ‘70s by Watson and Heilman, showing that the frontal lobe played some role in what he called the intention to move, and that if you knocked out one side you would produce an inability to move to that side. Posner proposed that there was not so much an inability to get to the opposite hemisphere but to disengage from stimuli like those cancellation targets on the right side—inability to disengage and move leftward. The attentional asymmetry idea was the one in which the right hemisphere is supposed to be able to direct attention both to the left and to the right side of space, whereas the left hemisphere only is able to direct attention to the right side of space. So if you knock out the right hemisphere, all you’re left with is an ability to orient to the right side, and that was the theory of why hemineglect tends to be more prominent in right hemisphere injury than left hemisphere injury. We explored this idea of the context effect that I just showed you with the different length lines, and this is the way we thought it probably worked. Here’s the way the patient performs on an index line. They see this line and the perceived line is this. They don’t have any kind of psychosis or memory problem, they’re simply bisecting to the line that they see here. Now if you add in a new line in a set, so now this is a longer line than this one, the new perception of the index line is a longer one. When they bisect that line it comes down here, a leftward

http://neuroscienceupdate.cumc.columbia.edu

12

Basic and Clinical Neurosciences

28th Annual Postgraduate Review Course December 3, 2005, through March 11, 2006

shift from here to here, so leftward shift by adding in a longer line. If it was just a matter of having sort of more cues over on the left side, then you wouldn’t expect the opposite to occur when you added in a shorter line, but that’s what happens. The response to the index line when you add in a shorter line is here. And why is that? So this is identical. When you add in the shorter line there is some idea that the universe of lines includes shorter lines, so this one is now perceived this way, and bisecting that line produces this rightward shift. We called this the context effect, and it looks like it’s probably a role of the right hemisphere to organize and prioritize and understand stimuli in context. If you or I were faced with this task, this doesn’t happen in normals, it doesn’t matter how many or what combination of lines that we see. If I gave you 6 centimeter lines and then added in a combination of 9, you’d simply say well, here’s a 9, here’s a 6, and the stimulus itself gives enough information to perform accurately on that task. And yet with right hemisphere damaged patients have this dissociation between the information that’s in front of them, and the inability to dissociate with the other stimuli that have appeared. It gets incorporated into an abnormal performance when the line is reassessed. We looked at line position as well and cueing to the left. You can alter performance by doing those type of manipulations. But when you remove those cues patients revert back to the same behavior. There is this continued dissociation in a variety of ways that we see clinically. Just to give an example, a patient who was a partner in a law firm, an intelligent guy as far as lawyers go, got to the hospital with a right posterior lesion. Up in his hospital room he said, “This is really bizarre. I don’t know why you guys have these weird phones, they only have two columns of numbers.” And we said, “Mr. So-and-So, obviously phones are always built the same way,” and when we pointed it out to him, “Oh, yes, I see, there are three columns of numbers there.” You know, knowledge of the world did not seem to influence his ability to take what’s in front of him and operate on that basis. It’s a function of the right hemisphere, even if you manipulate with cues or in individual situations, that dissociation is present, and that seems to be a characteristic of the right hemisphere that’s required for its function. So I will stop there, and thank you for your attention and take any questions.

http://neuroscienceupdate.cumc.columbia.edu

13