Creatures in the Brain

Abstract

f the nearly 2,000 brain-damaged O people who have been studied by cognitive neuroscientists at the University of Iowa College of Medicine in Iowa City, a handful have exhibited curiously fine-grained gaps in their knowledge about the world. Some of these patients suffer beastly lapses, failing to recognize dogs, horses, and other nonhuman animals. Others display an implement impediment-they have no idea what hammers, saws, or other tools might be used for. A number of patients are simply at a loss for words. Depending on what part of the brain incurred damage, they cannot recall the names of, for example, familiar people, places, animals, or tools, even though they can still place the individual items in the appropriate category. largest studies of these conditions to date, described in the April 11 NATURE, have convinced the Iowa scientists that separate brain systems handle distinct categories of knowledge. Other recent findings support the theory that the brain transforms some information into pictures in the head that flicker outside the realm of language (SN: 12/2/95, p. 372). Knowledge about conceptual categories and about words for items in those categories springs from separate cerebral sources, theorize Iowa's Antonio R. Damasio and his colleagues. When a person looks at a picture of a lion or a screwdriver, for example, certain brain systems enable the viewer to recognize, without pulling up a word, what he or she is seeing. Other neural circuits independently locate words that refer to a four-legged, furry creature with fearsome choppers or a slender metal bar with a flat end and a handle. The brain honors a general distinction between systems that handle concepts and those that handle words, Damasio contends. The brain also honors a distinction between particularly important conceptual categories and the words used to describe them. Natural selection may have etched into the human brain a heightened sensitivity to conceptual categories-a skill that aided Stone Age survival, Damasio proposes. Familiar faces, places, tools, animals, and foods are some of the categories that probably rest within their own cerebral niches, he maintains.