Conversations with Neils Brain|
The Neural Nature of Thought & Language
Copyright 1994 by William H. Calvin and George A. Ojemann.
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William H. Calvin, Ph.D., is a neurophysiologist on the faculty of the Department of Psychiatry and Behavioral Sciences, University of Washington.
George A. Ojemann, M.D., is a neurosurgeon and neurophysiologist on the faculty of the Department of Neurological Surgery, University of Washington.
If Language Is Left, Whats Right?
THE HALF-A-BRAIN TEST. Thats the name Neil had invented, by the
time we next met in the atrium. In the intervening week, hed experienced one of the
major diagnostic tests used on all epilepsy surgery candidates.
[FIGURE 23 A typical Woodrow-Wilson-type right brain stroke]
WILSONS STROKES had many of the other features we now associate with right brain
damage, such as defective body image. A person may be lying in bed, with the left side of his
body paralyzed, and still deny that anything is wrong. If you pick up his left hand, place it on his
right chest, and then ask him about it, he may deny that its his hand. He may become
obsessed with what another person is doing in bed with him.
[FIGURE 24 How left vision winds up in right brain]
In less dramatic cases, you can see what neurologists call neglect. While the right eye sees both to the left and to the right side of the nose, everything to the left of the midline is sent to the right brain. The right brain winds up with what is seen by both eyes of the left side of the visual world. And vice versa. Some patients with right-brain strokes tend to ignore anything on the left side of their visual world.
Others pay attention to objects on their left side but only if there is nothing else on their right side to compete for their attention. When driving a car and approaching an intersection, such a person may be able to see cars approaching from the left just as readily as cars approaching from the right, but only so long as they dont approach from both directions at once. If they do, the patient may ignore the car on the left and pay attention exclusively to the car on the right.
For some patients, such as my father after he had a small left parietal lobe stroke, the neglect is temporary; his lasted only a few days. But for others, it persists and becomes a big problem. Such patients must stop driving, but it is difficult to persuade them to do so; as far as they can tell, nothing is wrong with them.
Thats hard to believe. They really have no insight into their condition?
The very first neurology patient I ever saw, at a Saturday morning conference at Harvard Med, had this kind of problem. He seemed normal in every other way, and he was quite articulate. It was very impressive to see the neurologist stand behind this patient and bring his hands slowly forward around the patients head while the patient was looking straight ahead. The patient reported seeing the hand off to his left when it had reached halfway around his head. When the neurologist repeated the test on the right side, the patient saw that hand normally as well. But when the neurologist brought both hands around at the same time, the patient reported only the one on his right even though the neurologist was waving his fingers on the left, trying to attract the patients attention. The patient had stopped driving, at the insistence of doctors and family, but maintained that everything seemed normal from his point of view.
A self portrait painted by the German artist Anton Räderscheidt after he suffered a right-brain stroke illustrates what neurologists mean by neglect and defective body image. The portrait fills only the right half of the canvas, and in that right side, only one side of the face is accurately depicted.
If you dont have an internal image of the left half of your body, to say that nothing is wrong with it does have a certain logic, Neil said.
Agreed. But the problems caused by this kind of right-brain stroke are anything but trivial. Imagine a president who claims to be normal and still speaks in an authoritative tone of voice. He has no interest in participating in rehabilitation and does not know his own limitations. These are among the most difficult of all the brain-damaged patients to rehabilitate because they have so little insight into their problem.
Which raises the question, Where do we get insight?
Well, the psychotic patient often lacks insight into the illness. And we suspect that animals lack the mental capacity for such insight.
Maybe insight is part of consciousness, Neil said. Whatever that is. Something else to add to the consciousness list.
[FIGURE 25 Neglect of the left side of visual space]
UNUSUALLY GOOD FUNCTION OF THE RIGHT BRAIN is said to characterize those who
excel in the visual arts: painters, sculptors, architects, moviemakers. Neurologists suspecting a
right-brain stroke often try to test for elementary versions of these abilities.|
Neurologists like to draw a circle and ask the patient to fill in a clock face. The right-brain stroke patient knows that there should be numbers from one to twelve, but he is likely to crowd all of these into his good side, the right half of the circle between twelve and six oclock.
The patient just ignores the left half of the clock face?
Right. Ask such a patient to draw a cross, and it is likely to be drawn missing the left arm. You can get a house that has only details on its right side, a face with only one eye, a flower with only the half of its petals all drawings that the patient will claim are complete and normal sketches. The auto mechanic with such a stroke may be able to identify all the parts of an engine, but nonetheless be unable to assemble them. Subtle forms of this constructional apraxia are tested in the mental rotation of objects, seen in the multiple-choice questions on standard intelligence tests. These are all examples of visual-spatial functions.
The other deficit often present with a large right-hemisphere stroke is dressing apraxia: the patient cant get his arms into the sleeves, even though not paralyzed. The patient can name sleeves or pant legs and describe their use, but still cant perform, apparently because his image of his own body is defective. Even if Woodrow Wilson hadnt been partially paralyzed, it is likely that Mrs. Wilson would have needed to help him get dressed every morning.
So does sign language operate out of the right brain? Neil asked.
In a word, no. Deaf patients using sign language are just as impaired with left-brain strokes as the rest of us, and their sign language is just as unimpaired by right-brain strokes as ours is.
People have also wondered if the pictographs of some Asian languages involve the right brain. But a language, no matter how it is implemented, seems to be a language even for pictographs or hand gestures. And it depends primarily on the left brain, although some emotional aspects of prosody the way your voice rises at the beginning of a question or falls at the end of a sentence are affected by right-brain strokes. People with right-brain strokes sometimes talk in more of a monotone than they did before.
Clearly, right-brain strokes and left-brain strokes have different symptoms. You can see where the popular notions of left brain for language, versus right brain for spatial skills, have gotten their impetus. But the reality of biology is much more complicated. As George likes to say, the popular view is slightly more than half right. For every patient who has bilateral or right-brain language, there are 13 with left-brain language. Yet lateralization of spatial skills to the right brain is not the reverse. Nothing there is as strongly lateralized as even six to one.
Lateralized? Neil asked, raising his eyebrows.
Thats when functions with no left-right intrinsic aspect are not equally represented in both hemispheres. Functions like judging the distance of an object are not lateralized: both sides of the brain can do it, seemingly equally well. You usually measure lateralization by reviewing numerous patient records to see if right- and left-brain damage is equally likely to disrupt a particular function, such as knowing how to put on a shirt. Maybe five patients have dressing apraxias after right brain strokes, for every one patient with a dressing apraxia after a left-brain stroke. Only two patients show constructional apraxia after right damage, for every one with that symptom after a left-brain stroke. So constructional abilities are less lateralized than dressing abilities, but they are both lateralized, compared to depth perception.
Estimating distances sounds like one of those survival mechanisms, handy for hunting with spears and such.
The ability evolved much earlier than that. Lateralizations were originally thought to be uniquely human, but now theyre thought to go back to the monkeys, probably to a specialization for hanging on to the tree branch with the left hand while using the right hand to move food to the mouth. Monkeys have a minor version of our tendency to use the left brain for listening carefully to rapid sound sequences. So its a matter of the extent of lateralization, as well as the emergence of additional specialties such as language. And the corpus callosum can be a real bottleneck, simply because impulses travel rather slowly on that pathway. Coordination has its price.
Many patients with strongly lateralized language do not necessarily have strongly lateralized visual-spatial functions. Visual-spatial functions are more strongly lateralized in males than in females, probably because they depend on adequate levels of testosterone, the male sex hormone, during brain development, back when you were a fetus in your mothers womb. The difference between individuals in the degree of lateralization of different functions is just another example of how variable individuals are.
So does your degree of lateralization make any difference in your abilities say, as a painter?
Thats still an open question. Certainly some evidence suggests that more lateralization is associated with better function. When both sides of the brain have some language ability, certain types of language disability seem to be more likely. Stuttering, in particular. Its as if the two language areas cant coordinate their act properly, with all of those messages being sent back and forth through the corpus callosum.
I know. I worked for a company where the higher-ups were split, half on the East Coast, half on the West Coast. They could never make up their collective mind. People said that when we introduced a new product, we stuttered. Now I run a start-up with two other guys. We dont have that problem.
COMPARED TO THE LANGUAGE SUBDIVISIONS in the left brain, we know much less
about how these visual-spatial abilities are housed in the right brain. For the right brain,
were not even up to the nineteenth-century Broca-Wernicke level of theoretical summary.|
We find it difficult to even place neglect, denial of illness, and defective body image on a right-brain map or to be sure that their definitions dont overlap. The strokes that produce these visual-spatial problems tend to be large, with smaller strokes producing symptoms that are difficult to recognize by present methods. Defects of body image may be more likely with a stroke centered in the lower portions of the parietal lobe. Neglect is more likely with strokes higher in that lobe.
And thats consistent with the generalization thats made about monkeys, about what happens in analyzing the visual world after the information leaves the primary visual cortex. Damage to the underside of the temporal lobe tends to interfere with object recognition, but damage to parietal lobe tends to impair awareness that objects are even there and, of course, making movements toward them.
So temporal lobe takes care of what something is and parietal lobe handles the where?
Pretty much, though there is always overlap. For example, we know a lot about the parietal lobes Area 7 from the study of single neurons at least in monkeys, which probably arent very lateralized. With a little wiretapping, you can figure out what the neurons in Area 7 are interested in. They respond best to objects moving in the space just beyond your skin. Those neurons are truly egocentric.
Just outside you mean, like when I hold a fork?
No, mostly for things youre not touching yet. The next time youre on an airline flight, watch the flight attendants as they serve trays of food in very close quarters. You can watch the elbow of a flight attendant, poised inches away from the head of a person in the row ahead, and marvel at how well she seems to know where that persons head is, even though no longer looking in that direction. Out of sight, perhaps, but not out of mind.
I once asked a flight attendant about this. She claimed that she had eyes in the back of her head. Those eyes were probably neurons in her parietal lobes, contributing to a mental model of her extrapersonal space. The parietal lobes are probably what keep our visual experiences from looking like an amateur videotape, jerking from here to there. Our eyes do indeed jerk from here to there, even faster than a camera, but we dont perceive it that way. The seeming stability of our perceived world is porbably because it is, in large part, actually a mental model of our visual world that we update from all those jerky images we get.
THE RIGHT TEMPORAL LOBE functions are a little better known, compared to those of the
right parietal lobe. The right temporal lobe is interested in faces, among other things.|
The man who mistook his wife for a hat?
Not exactly. But the ability to recognize faces can be disrupted by temporal lobe strokes damaging either side of the brain, particularly if they involve the undersurface of the back part of temporal lobes. The famous patients who cannot recognize familiar faces, such as that of a spouse, may have a more general problem. Someone tested such patients on a series of pictures of cars, perhaps just as a control to testing them on portraits of people. The patients who couldnt pick out the faces of relatives from among the portraits also could not pick out a picture of their own car from among other somewhat similar cars. They can get the general category cars and faces but not unique examples. Their problem is with proper nouns, not ordinary nouns.
[FIGURE 26 Emotional facial expressions and right brain]
The right temporal lobe is particularly interested in the emotional content of the facial expression. This was discovered by using the fact that the image from the left half of your retinal images goes to the right brain. If half of a face is smiling, and the other half frowning, the side to the observers left is likely to be picked.
Better yet, you get yourself a set of pictures of faces, those of actors trying to portray an emotion using both sides of the face such as happiness, sadness, disgust, anger, and so on. George has tried stimulating the right temporal lobe while showing patients such actors faces depicting a standard emotion like disgust. Normally, the patients are quite reliable at naming the emotion being acted out. But they make mistakes when stimulated at some sites in the temporal lobe.
Do they see happy or angry? I mean, is the right brain a pessimist or an optimist?
Sorry, but they make errors in both directions. They just pick the wrong name, from among the possibilities. In the real world, that could lead to some serious misunderstandings.
So when another animal approaches you, and you misread its facial expression as one of friendliness rather than hunger, you arent likely to leave many offspring behind.
Yes and no. Basically, that turns out to be the wrong evolutionary argument. Primates usually dont eat others of their own species. And you dont need to check out the expression on his face to know that an approaching tiger presents a threat. But facial expressions are extraordinarily important among the apes, for judging the intentions of other members of the group. Thats how an solicits help in a dispute, judges what the dominant animal will permit without retaliation, or just finds a grooming partner.
Reading the emotional state of another member of your species is probably more important for sexual selection than for staying alive. Males that misread the body and facial postures of a potential mate get bitten or kicked. Thats the real law of the jungle. Those that are particularly good at judging readiness to mate may wind up with a lot more offspring. Staying alive is the name of the game when youre a juvenile, which, because of all that juvenile mortality, is when most natural selection occurs. But sexual selection may be more important in adulthood.
[FIGURE 27 Three-part model of facial recognition]
In the temporal lobes of monkeys, neurons can be found that are interested in faces but only faces of the appropriate species, and then only the eyes or the mouth. Nearly two-thirds of the neurons recorded from the human temporal lobe seemed to be interested in faces. In monkeys, there are a number of face-specialist neurons in the first fold below the sylvian fissure. And the monkeys are also lateralized for emotional face features, reacting more appropriately when the emotional clues are in the left half of their field of view.
We think there is a series of steps in recognizing a face as a familiar person. One of the higher-order visual areas, running along the underside of the temporal lobe, is particularly good at extracting facial features such as eyebrows. The front of the temporal lobe is thought to be involved with storing biographical information and proper names. A third area, in between them, is thought to be an association area that relates facial features to the biographical information. The right brain is far more involved with this job than the left brain.
So what about my storehouse of peoples names? Do I lose it with this operation thats going to shave off the front of my left temporal lobe?
No, but patients occasionally complain afterward that they have more trouble with proper names than with memories in general. We like to talk about areas of the brain having specialties, but the information is usually stored redundantly over a wide area. And removing the front end of one temporal lobe still leaves the other temporal tip.
So how about adding two and two together? Where do I do that in the right brain?
Either right- or left-brain damage can disturb arithmetic, particularly when it involves the parietal lobe. When you see disturbances in calculation abilities after a left-brain stroke, its usually complicated by some links with language abilities. Theres a constellation of symptoms known as Gerstmanns syndrome in which calculating fails but also the labeling of body parts, especially fingers. And those patients get confused about labeling things as being right or left.
Sounds as if they were counting on their fingers! But what about fancier counting abilities, balancing the checkbook, and so on?
There are some stimulation mapping studies on calculating abilities done in the O.R. George has occasionally asked patients undergoing right-brain operations to do some simple problems of addition, subtraction, division and multiplication while he stimulates sites in the right parietal lobe. He identified a number of sites where only one of these four functions was altered, and few sites where more than one was altered.
But no checkbook-balancing studies. The existing studies do suggest, however, that there are somewhat different neural systems for each type of calculation. With the evidence of difference between sexes in the degree of lateralization of visual-spatial functions its greater in males and now this evidence of specific right-brain mechanisms in mathematics, you can see how eventually we might answer some of the questions about why males are so overrepresented in the tail of the distribution for math abilities. Were talking here not about the average engineering student sweating his or her way through advanced calculus, but about those extremely gifted in mathematics, regardless of schooling or environmental emphasis, most of whom are male. And more are left-handed, allergic, and dyslexic than youd normally expect.
MUSIC IS SIMILAR TO LANGUAGE in its neurology, but some differences have been seen.
For example, George tells about a patient who was a country and western musician, a quite gifted
amateur. After he had the worst headache of his life, his doctors diagnosed a bleed, a
hemorrhage from an aneurysm in the left superior temporal gyrus, immediately below the sylvian
fissure. For a few days, the patient had some difficulty saying exactly what he wanted to. And
some of his words were nonsense, but this all cleared up. When his speech was normal, he tried
to sing one of his favorite songs and discovered that he couldnt do it. When the
neurologists explored this a little further, they found that he couldnt hum the melody or
sing the lyrics to any of his old favorites. But he could speak the words. And it works the other
way as well. Patients with Brocas aphasia can often sing words that they cant
Such findings suggest that music depends on both sides of the brain. After the front of the right temporal lobe is removed, there is some reduced musical ability memory for a set of tones or for rhythms. But thats only for amateurs. Disturbance of musical abilities in professional musicians usually takes left-brain damage. Its been suggested that as you gain proficiency in music, it is increasingly organized like a language, dependent on your left brain. But not on exactly the same areas as spoken language.
George has also wiretapped some neurons in the temporal lobe while having the patient listen to music. Short recordings of classical music caused their activity to decrease, sometimes to levels half of that before the music started. Classical music may be soothing, literally.
Im going to have to get you to explain the wiretapping business one of these days. But go ahead.
In music with a pronounced rhythm, activity of some neurons was entrained by the beat, just as if the neurons were clapping in unison. When rock music with a heavy beat was played, the activity of the neurons usually increased, and their firing patterns became even more emphatic. Some observers have commented, half seriously, that these neurons are firing in the bursting pattern reminiscent of that seen in recordings from epileptic areas.
As George likes to say in an ominous tone of voice, perhaps everything your grandmother told you about rock n roll is true.
LANGUAGE IS NOT SOLELY A FUNCTION of the left hemisphere, but the changes after
right-brain strokes are more subtle than the dramatic language changes seen after left-brain
strokes. When you hear a sentence, you have to make a mental model for what that string of
sounds represents. A full understanding of an utterance may well involve many right-brain
Right-brain stroke patients may not understand all of the connotations of a common word. They may become more literal-minded, having trouble appreciating figures of speech. Ask them to paraphrase a short story, and they may repeat it verbatim without making changes. They have trouble with antonyms. The spontaneous speech of such patients is often rambling.
As you might expect from the flat tone of voice used by many right-brain stroke patients, they may also have trouble interpreting the speakers tone of voice. Testing them on narratives is particularly revealing. Unlike aging patients who are quick to admit when they are uncertain about a memory, right-brain stroke patients seldom indicate a lack of confidence when making mistakes in recalling test stories. They are particularly bad about retelling a story in the right order, tripling the normal number of errors. This is almost as bad as the patients with left-brain strokes causing aphasia.
So if they cant keep the story straight, jokes must be wasted on them. They wont be surprised at the punch line.
Yes, subtlties go right past them. Their own attempts at humor are often crude, off-color, or inappropriate. So while the left brain may be more involved with the building blocks of language, the right brain is quite helpful in interpreting it all.
Conversations with Neil's Brain: |
The Neural Nature of Thought and Language (Addison-Wesley, 1994), co-authored with my neurosurgeon colleague, George Ojemann. It's a tour of the human cerebral cortex, conducted from the operating room, and has been on the New Scientist bestseller list of science books. It is suitable for biology and cognitive neuroscience supplementary reading lists. ISBN 0-201-48337-8.
|AVAILABILITY widespread (softcover, US$12).|