Copyright © 2007-2017 Russ Dewey
A rare brain syndrome, prosopagnosia or "facial blindness," is notable because of its highly specific symptom: inability to recognize faces. Apparently it is caused by damage to the area between the occipital and parietal lobes on both sides of the brain.
Cole and Perez-Cruet (1964) describe the symptoms of a human with prosopagnosia:
The patient was presented with a single picture of himself and asked to identify it. He thought that it "possibly" was himself but was uncertain.
He was then handed a picture of the examiner and though we had spent many hours together and were now face to face with the picture in front of him he was unable to identify the picture....
At the end of the test session he was again presented with a picture of himself and asked, "Have you ever seen this fellow?" He replied, "Hmmm, well down through the chin there's a groove, but I can't say who it is." (p.47)
What is "prosopagnosia"?
Oliver Sacks, the well known author who specialized in neuropsychology themes, revealed shortly before he died in 2015 that he was a prosopagnosic. One of the cases he had described in his books was himself, although he did not say so at the time.
Problems in spatial orientation are produced by damage to the parietal (pear-EYE-it all) lobe, typically in the right hemisphere. Spatial abilities are used when one forms a mental map of an area, or when one figures out how shapes will fit together.
Patients with parietal damage in the right hemisphere may lose their ability to perform spatial processing. For example, in the acute phase (soon after injury) they get lost easily. If they leave their hospital rooms to get a snack, they may wander aimlessly until a helpful person shows them the way back to their room.
One family realized a middle-aged man was ill when he got lost on the way home from a factory, a route he traveled twice a day for thirty years. Doctors found he had suffered a stroke in the parietal lobe of the right hemisphere.
What problem is caused by parietal lobe injuries?
Gradually, as time passes, patients with parietal injuries show fewer symptoms. This recovery of function is typical of many brain-injured patients.
In general, the first six months following brain injury are critical. If a patient fails to improve during this time, the long-
After a few months, the typical patient with moderate parietal lobe damage shows almost no symptoms. However, a residual deficit (a remaining problem) can be demonstrated with a simple test, described by Teuber (1963).
The doctor gives the patient a card with a little map on it. The map consists of nine dots, in rows of three, connected by an irregular line.
On the floor of the examining room is a similar pattern of nine dots, in three rows of three. The patient attempts to follow the path shown on the card, walking between the dots on the floor.
How did Teuber test for parietal lobe injury?
Parietal patients have difficulty doing this. They reach a corner, turn around, and (no longer able to relate the card to the floor pattern) they get lost.
The corpus callosum is the main fiber bundle connecting the two hemispheres of the brain, allowing the two halves to communicate. In the following picture, you can see a mid-saggital section (a view of a brain which has been sliced between the two hemispheres).
Note that the wrinkles or convolutions extend down from the top of the brain until they reach the whitish area in the middle, the corpus callosum. That is the only place where the two cerebral hemispheres are connected.
What is the corpus callosum?
A mid-saggital section (brain split down the middle)
When the corpus callosum is cut, the hemispheres can no longer communicate directly. This is the split-brain operation.
What was the split-brain operation and what were the results of it?
The split-brain work was pioneered by Roger Sperry, who perfected the operation in animals. In the 1960s it was used on humans.
Doctors decided to disconnect the two hemispheres of a 48-year-old war veteran in hope of relieving his uncontrollable seizures. The results were so spectacular and important for brain science that Sperry ultimately received the Nobel Prize, 20 years after the first split-brain operation.
Some patients acted as if they had two different personalities in the two hemispheres after the operation. Gazzaniga (1970) wrote:
Case 1...would sometimes find himself pulling his pants down with one hand and pulling them up with the other. Once, he grabbed his wife with his left hand and shook her violently, with the right hand trying to come to his wife's aid in bringing the left belligerent hand under control.
Once, while I was playing horseshoes with the patient in his back yard, he happened to pick up an ax with his left hand. Because it was entirely likely that the more aggressive right hemisphere might be in control, I discretely left the scene, not wanting to be the victim for the test case of which half-brain does society punish or execute. (p.107)
Why did Gazzaniga "discretely" leave his patient's backyard?
Reuter-Lorenz and Miller (1998) noted that a split-brain patient has "two minds in the same cranium" and may experience conflicts such as one hand placing items in a grocery cart while another returns them to the shelf.
However, these conflicts decrease with time after the operation. "In particular, it has been shown that one hemisphere is able to inhibit, or gate, the responses of the other." Therefore, the more competent hemisphere tends to take control of performance on a given task.
Split-brain patients were always tested intensively before the surgery, and the operation was performed "only if all other opportunities for permanently abolishing the seizures appeared closed" (Gazzaniga, 1970).
Why would a split-brain operation prevent seizures? In these patients, the epileptic activity bounced back and forth between the two hemispheres, across the corpus callosum. Cutting the corpus callosum prevented the activity from building up, greatly reducing the number and severity of seizures.
Under what circumstances was the split-brain operation performed?
Although the operation worked in the sense that it abolished the seizures, it was obviously a radical and irreversible procedure. Within a few years after the initial split brain operations on humans, drug therapies were found to provide an alternative for most patients, and the split brain operation became rare.
Gazzaniga (1998), reviewing 30 years of split-brain research in humans, concluded that his first three patients were quite unusual. They possessed language abilities in both hemispheres. The majority of split-brain patients showed no language comprehension in the right hemisphere.
How were Gazzaniga's first three patients unusual?
Split-brain patients were sometimes studied with an apparatus designed to take advantage of the fact that each half of the visual field projects to the opposite side of the brain. A split-brain patient was seated in front of a screen and told to look at an "X" in the middle of the screen. Next a picture is flashed on the screen, too quickly for an eye movement to occur.
With the patient's gaze fixated at the center point, everything to the left of the X would go to the right hemisphere. Everything to the right of the X went to the left hemisphere. Using this apparatus, Sperry and his student Gazzaniga were able to send messages to one side of the brain or the other.
The split-brain apparatus showed different scenes to the two hemispheres
Suppose the right brain sees a snowy scene, while the left-brain sees a chicken leg. The patient is given a multiple-choice test consisting of four pictures that might relate to the scene. One of the four alternatives is a shovel; another is a chicken.
Asked to point to a symbol corresponding to the image on the screen, each hand points to a different symbol. The right hand points to a chicken, because the pattern on the right side of the screen is a chicken leg. The left hand points to a shovel, because the right hemisphere sees only the snow scene.
To repeat: the left hemisphere, which controls speech, sees only the chicken leg. If asked why the left hand (controlled by the right brain) pointed to a shovel, the talking hemisphere does not know! But it quickly makes up an answer, such as, "Well, you have to clean up after those chickens."
This is an example of a rationalization: a rational but false explanation. It occurs smoothly and quickly, suggesting a well-developed talent in humans.
Perhaps we frequently have no idea why a neural event occurs, for example, why a thought or feeling occurs to us. If we have to explain our behavior, we make up something that sounds reasonable.
What form of "instant rationalization" occurs in split-brain patients?
In a 1998 30 year review article, Gazzaniga affirmed the tendency of the left hemisphere to confabulate or rationalize. The left brain (the talker) quickly made up reasons for unexplained activity controlled by the right hemisphere, in all the split-brain patients he studied.
If distinct parts of the brain perform distinct functions, we might expect to people differing in their talents depending on which areas excel. Nobody is good at everything, and most of us have weaknesses corresponding to particular brain modules, just like we have strengths corresponding to other brain modules.
For example, tone deafness is what neuropsychologists would call a selective deficit. A person with tone deafness cannot "carry a tune" because he or she does not hear melody like other people.
When the same skill center is highly developed, the result is an acute sensitivity to melody and sometimes perfect pitch. Perfect pitch is the ability to identify the pitch of a note (C, D, F-sharp, etc.) when notes are played in isolation, without additional cues. Some people have this ability naturally; others try to learn it from training courses.
A person can be a selective genius (a savant) or a person can have a selective deficit (missing or defective skill), depending on how various parts of the brain function. Studies of savants and brain damaged patients led researcher Howard Gardner to a theory of multiple kinds of intelligence described in his book Frames of Mind (1983).
Gardner used data from brain-injured patients and also from special populations such as autistic savants and children with learning disabilities. These individuals sometimes have exceptional skills in one area but deficient skills in another.
In the end, Gardner identified seven separate and discrete forms of intelligence. In the language of neuropsychology, these skills are doubly dissociable, meaning that each can be altered or disabled without affecting the others. In this sense they act as distinct modules in the nervous system.
What does it mean to say skills are "doubly dissociable"?
1. Linguistic intelligence is a facility with words, a sense of how to combine them to express meaning clearly or beautifully. For example, poets are advanced in this type of intelligence.
2. Logical-mathematical intelligence is an ability to manipulate abstract thoughts such as those involved in logic, mathematics, and science.
Gardner (1993) commented, "Jean Piaget, the great developmental psychologist, thought he was studying all intelligence, but I believe he was studying the development of logical-mathematical intelligence."
3. Spatial intelligence is "the ability to form a mental model of a spatial world and to be able to maneuver and operate using that model." Sailors and sculptors both use this kind of intelligence.
4. Musical intelligence is, of course, the ability to comprehend, produce, and enjoy music. Mozart is a famous case of a person with high musical ability in childhood.
5. Bodily-kinesthetic intelligence is "the ability to solve problems or to fashion products using the whole body or parts of the body," exemplified by "dancers, athletes, surgeons, and craftspeople."
6. Interpersonal (social) intelligence is the ability to understand and work with other people, shown by successful salespeople, politicians, teachers, and religious leaders.
7. Intrapersonal intelligence is the ability to "turn inward" and develop insight from personal experiences: to form accurate knowledge of oneself and use it to live more effectively.
What are the types of intelligence identified by Gardner?
Gardner later added an eighth category for sophisticated pattern recognition. He described that talent as the ability to recognize natural objects such as variaties of plants and animals.
Such skills would have been at a premium in our ancestral environments. A person exceptionally skilled at spotting edible or medicinal plants, for example, would have a highly valued form of intelligence.
What eighth category did Gardner add later?
These eight categories are large-scale, major categories of intelligence. They can be subdivided further. For example, a person who might be good at one type of math but poor at another.
Another person might be a great essayist but a lousy poet, although both involve linguistic intelligence. Clearly there are multiple forms of intelligence within each of the broader categories of intelligence identified by Gardner.
Cole, M. & Perez-Cruet, J. (1964). Prosopagnosia. Neuropsychologia, 2, 237-246.
Gardner, Howard (1983) Frames of Mind: The Theory of Multiple Intelligences., New York: Basic Books.
Gazzaniga, M. S. (1970). The Bisected Brain. New York: Appleton-Century-Crofts.
Gazzaniga, M. (1998, July) The split brain revisited. Scientific American, vol, 50-55.
Reuter-Lorenz, P. A. & Miller, A. (1998). The Cognitive neuroscience of human laterality: Lessons from the bisected brain. Current Directions in Psychological Science, 7, 15-20.
Teuber, H. L. (1963). Space perception and its disturbances after brain injury in man. Neuropsychologia, 1, 47-57.
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Copyright © 2007-2017 Russ Dewey