5. MAPPING BRAIN FUNCTIONS

The Evidence of Damage to Specific Brain Regions

ANTONIO R. DAMASIO, MD

The second presentation of the conference, from Antonio Damasio, provides concrete examples of correspondence between the brain anatomy and functionality. Damage to specific regions of the cerebral cortex proves to have precise and predictable effects on human perception, recognition, and language. Such correspondences are fundamental to the Western scientific understanding that consciousness exists solely as a property of the complex architecture of the connections between neurons.

ANTONIO DAMASIO: I have some concrete evidence for Western science’s view on the brain. I have selected a few examples of changes in mind processes in individuals who suffer from localized brain damage. If one of us suffered a stroke, and had thereby lost a particular area of the brain, that would provide an opportunity to study the results of the loss of that part. We would learn what the brain can do in the absence of that particular part. I shall present examples of what the consequences are for persons who lose certain brain areas as opposed to those who lose other areas.

A very important fact is that the surface of the brain, the cerebral cortex, is made up of distinctive areas, each of which has characteristic functions. Cortical areas appear similar on the outside, but when we study them under the microscope, they reveal specialized organization and distinctive neuronal circuits that cooperate with each other. Thus, a million cells here and another million cells there can communicate with each other by means of very specific connections. There is no possibility for any one group to talk to all other cells, but rather specific groups talk to one another and receive responses from other particular groups of cells. The arrangement is exceedingly orderly and systematic: certain strict principles of organization obtain. There are distinctively different patterns of intrinsic organization and external connections for each particular cortical area. There is a distinctive architecture, area by area.

At this point, Dr. Damasio projected a photograph of a building. The left half of the image was essentially a black and white photograph, while the right half appeared in full color.

ANTONIO DAMASIO: What this picture depicts corresponds to the subjective experience that one particular patient described to us, namely, the loss of color vision on the left visual field, with color vision preserved on the right. This is an experience that many patients have. They report loss of the ability to see color in one half of their visual field, left or right, rather in the same way that you can lose color on a television screen if you turn the color knob. You can still see different shapes, and perceive depth, and know whether an object moves. But you cannot see color in half the visual field.

We have studied the brains of many such individuals over several years and found that there is one critical area on the inner side of each hemisphere in the brain, damage to which leads to this kind of half-field color loss. On each side of the brain, this area is responsible for providing colored visual experiences to the visual field on the opposite side. It is important to observe that when you encounter similar damage to cortex elsewhere in the brain, no color loss occurs. We can confirm this localization in living patients using magnetic resonance images (MRI).

Dr. Damasio showed the group a series of MRI brain scans with the fusiform gyrus marked in red, noting that such images are obtained without doing any harm to the patient.

ANTONIO DAMASIO: Once you lose this particular area, and this alone, your visual experience will be normal, except for the loss of color in one half-field. There is no possibility of learning or otherwise restoring the experience of color vision in that affected field. If you produce equivalent cortical damage elsewhere, no such loss will occur. In other words, there is a one-to-one relationship between color loss in the corresponding half-field of vision and this particular area of cortex. This area controls a color-dedicated neuronal system.

We find a similar color vision deficit from removal of the equivalent cortical area in the brain of the monkey. Further, we know that neurons in this region in the monkey are responsive to color presented in the contralateral visual field. In other regions neurons may be responsive to visual shape or motion, but not to color, or only incidently to color, as in passing along color information to this particular area. In this region, therefore, there are neurons which specialize in the color processing necessary for conscious perceptual experience of color.

DALAI LAMA: It is possible to see shape without color, for example, in the case of someone who is color-blind, but is it possible to see color without shape?

ANTONIO DAMASIO: That is an interesting point. If other parts of the visual system were damaged and this particular area were left intact, we might suppose that we could perceive impressions of colors, such as seeing blueness, redness, colors without borders. Yet color perception is characteristically confined to specific shapes: for example, this table, your garment, and so on. When we lose the ability to see shape, we also lose the ability to see light, and we develop a blind field. It is evident that the color-bearing signals traverse most visual pathways but that they contribute to conscious perception of color as an expression of cortical analysis in this location.

Now I want to show you another interesting example of mind changes resulting from a stroke. With the lesion demonstrated here (in the medial occipital temporal region) the patient loses the ability to recognize familiar faces. The patient is unable to recognize the faces of friends, members of one’s own family, even one’s own reflection in a mirror, nor can the patient recognize the faces of familiar public personae. This deficit in facial recognition is specific to particular cortical areas. It is only when you damage this particular area that this phenomenon occurs; damage elsewhere does not cause this effect.

Something quite interesting happens in patients who lose the ability to recognize familiar faces consciously. They are still capable of exhibiting recognition of which they are entirely unconscious. One way of learning about this is to measure skin conductance in such patients. It is known that normal individuals in the process of recognition generate a dramatic shift in electrical resistance of the skin. If I were to encounter Pat Churchland, my conscious recognition of her would be accompanied by just such a galvanic skin response. If we encounter someone with whom we have had no previous experience, there is no matching recognition and there is no galvanic skin response, or only a small, weak response. A patient who cannot consciously recognize faces still produces a galvanic skin response which occurs only on exposure to familiar faces, signaling an unconscious physiological response that accompanies recognition at some unconscious level. With a specific type of brain lesion, we may be consciously oblivious of recognizing someone while at the same time there will be physiological signs of recognition at a lower level of brain organization, accompanied by a galvanic skin response. This indicates clearly that at some unconscious level I do know that person.

DALAI LAMA: The person in this case fails to recognize a specific face, but does he recognize that it is a human face?

ANTONIO DAMASIO: Absolutely. That is an important point. The person knows not only that it is a human face, but also whether it is a smiling or a sad face, a good-looking or an evil-looking face, old or young, male or female. And yet, the conscious identification of the familiar face is not available. At some deeper level, however, there is a specific, personalized, unconscious discrimination.

Now we are considering levels of consciousness in physiological terms and at the level of neuroanatomy. When a patient has suffered the loss of this particular region of cortex, he cannot muster conscious recognition. The patient is unable to use features that identify that unique individual according to the patient’s unique personal experiences—the features that evoke the memoranda that identify that individual. Yet, at a lower level of neuronal processing, the patient generates an electrical skin response that is unequivocal, unmistakable evidence that in fact his brain knows that person from prior experience. It is a sure sign of previous encounter and thus a sign of unconscious recognition.

The existence of evidence of this sort strongly reinforces the point that different regions of the brain are making decisions, and are contributing in different ways to the integrative mechanisms that support consciousness.

CATEGORICAL DISTINCTIONS IN CONSCIOUSNESS

Is there or is there not a characteristic difference in brain structures and functions involved when we learn to represent, recognize, and categorize different types of objects?

Let’s consider responses to a human face, to an object such as a table, to an animal, or to a flower. We now have very solid evidence to indicate that the brain areas, or systems, specifically concerned with human face processing in conscious experience are entirely distinct in location and response from systems concerned with man-made objects, such as tables or chairs or glasses. And those in turn are distinct, also, from systems concerned with representation, recognition, and categorization of living things such as animals and flowers. Our evidence comes from the study of patients in whom we recognized that damaging one area precludes or eliminates the recognition of animals and flowers and other natural objects, but does allow the patient to respond quite rapidly to a long list of inanimate artifacts; for example, that this is a pointer, that these are glasses, that this is a table, and so on.

We also have patients who lose their ability to recognize, for instance, a manipulable object, which can be held and changed in shape by use of one’s hands, and yet they can recognize natural objects. This indicates to us that there are distinctions, to a greater or lesser degree, among different categories of objects that are represented in our brains. The evidence indicates that different categories of stimuli are processed differently in respect to how they are stored in memory and how they are retrieved from memory.

There are, of course, other distinctions. For instance, take our ability to recognize musical sounds and to learn melodies. Musical abilities occupy distinctly different brain regions, and I may say, engage different brain strategies from any other categories of stimuli and brain processing capabilities. You can destroy selectively the ability to recognize melodies and to identify pitch correctly, and yet preserve other categorizing skills.

The ability to learn a motor skill involves entirely separate brain regions from those involved in the ability to recognize faces and is likewise distinctly separate from those involved in learning words. In general, language is quite a separate function, distinguished from the rest of these processes by its special location and functional organization.

Another area in which there is a critical difference has to do with the complexity of an object. For instance, picking up on your Holiness’ earlier question, when I look into Larry Squire’s face, I instantly know that it is a face, a human face, and masculine. And I could even make a suggestion about what, for instance, he might be like as a person. All of that is far simpler in terms of mental determination than saying that this is the face of a particular individual and still distinct from the further determination that identifies Larry Squire’s face as familiar to me. For that particular aspect of brain processing, Larry Squire’s unique physiognomy, there are uniquely defining features, united in a particular facial representation and connected with a complicated and unique ensemble of associated experiences.

Evidently, the brain is continually pigeonholing objects into broad but distinctive categories: that a flower is a natural object; that a face is a natural object; that a car is an unnatural, man-made, mechanical object. This prompt broad categorization allows the neuronal representations of these different sorts of objects to be separately distributed in the brain for further processing and further categorization by separate, more specialized, areas of the brain. Following “first echelon” initial categorization and immediate channeling to more specialized brain regions, more refined and specialized brain processes apply additional discriminanda by which the objects are further specified and individuated.

With respect to human faces, there are millions of male faces, millions of male faces with beards, and millions of male faces with beards and glasses. These are obviously easy discriminanda, simple to apply, and they enable initial brain processing to arrive rapidly at useful general categorizations. When it comes to knowing that this face is Larry Squire’s, that that object is the Eiffel Tower, that that dog is Lassie, that this flower is a cymbidium from my garden, this requires particularizing strategies in specialized locations that can make use of unique, locally stored information. Eventually, to be recognized as familiar, the individualized objects of whatever category have to be linked to remembrances involving unique personal experiences.

So there are evidently numerous ways by which the brain is able to recognize and distinguish these categories in an almost infinitely complicated universe. Separate and distinct brain systems are engaged in managing successive stages of distinctive kinds of categorization.

My final example shows that brain damage in a different brain system, rather than producing a change in the recognition of faces, or objects, or colors, produces a disturbance in the way the patient attends to different objects and the way he examines the visual field. If we are afflicted by this kind of brain damage, called the Balint syndrome, we see the world as though we were perpetually peering through fog, into a visual field in which parts of objects seem to merge into one another and nothing is clear. In these cases, the patient can never attend to more than one particular part of the visual field at a time. The Balint syndrome is a major perceptual disturbance, but curiously, it permits recognition of faces and colors. The affected individual complains of not seeing things clearly and seeing only bits and pieces at a time. Yet, when a familiar face or image comes into a limited field, they say almost immediately, “Aha! There is so-and-so,” and identify a particular person correctly. And when the color red comes into a functioning part of their visual field, they describe seeing the red distinctly.

Again, this points to the tremendous specialization of particular brain structures and operations, some of which process color, others form, others motion, and still others categorize whole entities. These regions put various perceptual and mnemonic components together, presenting consciousness with “whole things” represented as categorized, coherent, integrated recognizable objects.

DALAI LAMA: This deficit involves only damage to the brain, not to the sensory faculties such as the eyeball?

ANTONIO DAMASIO: Exactly. If you lose both eyes, you are obviously blind. But in your inner consciousness, you would not have any disturbance of this sort. If you become blind, you can still think in color. You can still think of people’s faces, by type or as particular individuals. And you can still imagine a landscape in a perfectly coherent and dynamic way. If you lose only one eye, you only lose binocularity, but your visual field is nearly as complete as before.

The patients I report as seeing everything in a fog are not suffering sensory disturbances, per se. They are suffering disturbances of higher order integration of perceptual information as processed by different parts of the brain. Although the world is put together for us in consciousness, it is assembled from a distributed, analytical, decision-making apparatus which has a surprisingly marvelous gross, microscopic, and ultrastructural architecture.

Another quick example—I think you will enjoy learning about this example because it is quite stunning. If you lose a particular very small area in the left hemisphere, you find among Westerners who speak Indo-European languages a loss of the ability to read, but not of the ability to write. The patient looks at a text and is able to say, “Well, indeed, there are words here, there are letters, but I don’t know what they mean.” They just look at the text line by line without being able to read it. But when I ask them to write down a text, which I dictate, they fully comprehend the message and write it out correctly. This is because they are working with a different information system in their brain, one which allows the patient to control the hand and write cogently. If, two minutes later, I ask the patient to read what he has written, he cannot read it. He is absolutely unable to do so.

ROBERT LIVINGSTON: You might be able to remember it, perhaps, but you could not read it.

ANTONIO DAMASIO: Yes. This only happens with damage to the left hemisphere. If you have damage in the same discrete area on the opposite side, on the right side, it will not have this effect.

Now it is extremely interesting that if a person speaks a language that is not phonemically based, with a combination of letters for each sound, but instead a language written with ideograms, where a character corresponds to an object, a word, or an idea, then the patient will not lose his ability to read text after left-sided damage. But the patient will lose the ability to read the ideographic language if he sustains a lesion in the corresponding part of the right hemisphere. Thus, following a lesion in his left hemisphere, a patient would not have a reading problem if he has learned a language in which there are ideograms as opposed to letters representing phonemes. And a person with similar left hemisphere damage is not handicapped from understanding sign language, which is a visual language based on the production and interpretation of signs using hand motions and gestures. Once again, this emphasizes how separate and distinctive are the various streams of brain information processing.

ALLAN HOBSON: How does the area represented in this brain lesion differ from that which is concerned with color perception?

ANTONIO DAMASIO: It is a slightly different lesion in terms of size, and the lesion that causes achromatopsia is localized to the gyrus. It does not involve the depths of the sulcus. However, if the lesion goes into what Dr. Hanna Damasio calls the paraventricular area, then you have alexia, the inability to read. If the lesion is further forward, you get color anomia, in which case colors are perceived but without the patient being able to name them.

THE BRAIN’S REPRESENTATION OF BODY AWARENESS

There are patients who have damage to structures in the right hemisphere, as opposed to the left. And when the damage on the right side involves areas in the parietal lobe, and sometimes in the frontal lobe also, something quite peculiar happens in relation to the patient’s awareness of his own body. The patient can read, write, talk, and be very articulate, but if there is a pain or paralysis affecting his body; the patient is unable to report, in fact unable to realize, that he has any such a disorder. And, the patient does not suffer the normal anguish and concern that one normally associates with cancer or a paralytic disorder.

I think there is interest on the part of Buddhists to discover that there are areas of the brain that control the processing of body awareness. There are areas in the brain that integrate summary representations of body imagery, in much the same way that there are areas that provide smoothly integrated representations of the visual world. Somehow these parietal and frontal areas are important for us to feel the effects of changes going on in our own bodies.

I would like to suggest that when we distance ourselves from our body in meditation, something happens in our brains that allows this conscious perception of separation to occur. It appears to allow perceptual processing to change connections between areas dedicated to body imagery and the rest of the brain. Something evidently happens that divides consciousness and separates perception of one’s own body from perception of other events of which we are conscious. This, of course, would be an entirely normal process, but one that some of us would be unable to achieve without disciplined training. I wish I could do that, to be able to make a switching of connections in a physiologically reversible way, as a Buddhist might in a normally functioning way, as opposed to simply determining neurologically that such a separation can occur as a consequence of brain injury or stroke.

ALAN WALLACE: As interpreter, I am concerned with your terminology. You said when a person with this type of damage to the right hemisphere of the brain becomes subject to cancer or paralysis, the person doesn’t suffer. Are you saying that the person does not feel physical pain, or does not feel the mental anguish that normally accompanies that pain or paralysis?

ANTONIO DAMASIO: The person can feel a sensation that he or she actually describes as pain, but without experiencing the usually accompanying suffering.

ALAN WALLACE: You mean mental suffering?

ANTONIO DAMASIO: First of all, the patient looks calm and unconcerned. When asked whether he suffers any anguish, he will ask, “Anguish about what?” You then ask, “Do you feel pain?” In some of them, if there is a pain syndrome, they will say yes.

ROBERT LIVINGSTON: Would you like to say something about personal neglect syndromes?

ANTONIO DAMASIO: There is a condition occurring with particular lesions, especially involving the right hemisphere, although they can also involve the left, in which the patient loses the ability to pay attention to bodily events that are occurring on the other side of the body. So, if I have a brain lesion in my left hemisphere, I may be normally attentive and congruent about what happens on either side of my body and the space around my body. But if the brain lesion is in my right hemisphere, and if, for example, someone comes into my peripheral field of visual from the opposite (left) side, I will not automatically look in that direction and pay attention to that field of view. Likewise, I will be less attentive to sounds, expected or unanticipated, originating on that side of me. This is “neglect.” You would call it hemi-neglect, affecting the left side of the patient’s body and the left side of the world from the patient’s point of view.

Neglect actually affects not only the way we perceive the world but the way we perceive our own minds. This is quite striking. We could do the following experiment with a person who exhibits this sort of neglect: Suppose that such an afflicted person, after sitting here at our table, were asked to close his eyes and recall who is seated around this table. A person with right-sided neglect, for example, would name only the individuals seated on his own right side. When asked, “And who else?” the patient would answer, “There is no one else.”

However, if you then ask the patient to imagine sitting at the opposite side of the table and to describe, with his eyes still closed, who is seated at the table, the patient would name only those seated on the right side of his imagined position—the same individuals he was previously unable to identify. And again he would be unable to name those on the left side of his imagined position.

So in the patient’s mind, the representation or evocation that can be elicited by mental reorientation is also affected. This is a disturbance that affects not only one’s perception but the geometry involved in conscious processing of the recall of perceptual experiences.

DALAI LAMA: Are there cases in which brain damage can be cured, or may the brain in some situations heal, or restore, itself? If some portion is damaged and cannot function properly, might other parts of the brain eventually come in to help perform those functions?

ANTONIO DAMASIO: Substitution is a very interesting point. It is true only for certain abilities and for certain faculties.

DALAI LAMA: Is it impossible for substitution to occur in this condition?

ANTONIO DAMASIO: That’s true. In most of these cases, they cannot recover normal function. It is true, for instance, for motor function, that if you become paralyzed, generally you will recover some strength. The reason is that the motor system is organized at many different levels, and if you lose motor function organized at one level, other levels may be able to compensate to a considerable degree.

But for certain abilities, like face recognition or language, these are highly sophisticated, highly corticalized abilities. They are organized asymmetrically in the two hemispheres, with little duplication or overlap between them. Then little or no recovery can occur. For instance, if a very skilled musician loses the ability to perceive pitch or to recognize melodies as a result of a stroke, that skill is lost forever.

We have studied musically talented patients. We have followed the case of a professional opera singer who suffered a stroke in his right hemisphere affecting his acoustic processing systems. His ability to recognize arias, even from operas he had sung on stage for years, was entirely lost. His ability to sing on pitch was also lost. But, he can still go to the piano, with a score in front of him, and play perfectly, without error. There is preservation of his ability to read musical notations and to control his piano playing using hands and feet appropriately. He is able to reproduce music correctly on the piano from musical notations; he is able to match movements appropriate for what is indicated on the musical score. But if he tries to accompany himself at the piano and sing, he cannot perform in that way. He cannot control his own musical instrument, his voice, although he can govern his hands musically in playing the piano.