We can readily recite the properties and functions of a familiar object: fire trucks are red, they have sirens, hold ladders, have four wheels, are used to put out fires, and so forth. This sort of object knowledge is represented and stored in the neural networks of the brain, and much recent research in cognitive neuroscience has concerned the physical organization of such knowledge. Is all our knowledge crammed together in one part of the brain, or is it spread out over many areas, perhaps according to a set of rules? The controversy continues, but there is a growing body of evidence that knowledge about certain categories of objects, such as animals and tools, is at least partially segregated in the brain. The most compelling evidence comes from studies of patients with damage to particular brain areas, often due to strokes. Some patients, for example, appear to have lost their knowledge of tools, but have relatively unimpaired knowledge of animals. This suggests that the damaged part of the brain formerly contained their knowledge of tools. The opposite pattern of impairment can also be found, suggesting that knowledge may be organized in the brain according to category.
In this issue (Nature Neuroscience, Vol. 4, No. 6, 01 Jun 2001), Alfonso Caramazza and colleagues present evidence that knowledge is also organized according to modality. They describe a remarkable brain-damaged patient who has lost much of her knowledge about the colors of objects, while retaining other aspects of object knowledge. This patient was just as good as the average healthy person at answering questions like "Which has legs, a cat or a trout?" or "Which is shorter, a pig or a horse?". In contrast, when asked questions like "Which is red, a tomato or a tangerine?" or "Can a canary be yellow?", their patient performed far below normal levels. The patient had brain damage to the middle regions of the temporal lobe in the left hemisphere, suggesting that these regions may contain knowledge about object color. The deficit observed was specific to color object knowledge. The patient was flawless in matching stimuli of similar colors, pointing to patches of colors named by the experimenters, and naming the colors of objects she could see. Thus her perception of colors was unimpaired. Confirming other research, this suggests that knowledge of objects may be independent of the brain systems involved in perceiving objects. This patient's brain damage has provided an important new clue to how knowledge is organized and stored in the brain -- knowledge about color appears to be organized separately from knowledge about other aspects of an object's appearance and function.
Dr. Alfonso Caramazza
Cognitive Neuropsychology Laboratory
William James Hall
33 Kirkland Street
Cambridge, Massachusetts 02138
tel: +1 617 495 3867
fax: +1 617 496 6262
(C) Nature Neuroscience press release.
Message posted by: Trevor M. D'Souza
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