Tracking down bodies in the brain

A specific patch of tissue on the right side of the brain’s visual cortex takes

charge of recognizing human bodies and body parts, contends a team of researchers

led by psychologist Paul E. Downing of the University of Wales in Bangor. This

body-processing hub lies near one region already linked to face recognition and

not far from another that specializes in telling one place from another, the

scientists say.

The researchers made their find by studying 19 volunteers with a brain-scanning

device that measures surges and declines in blood flow throughout the brain. Those

changes reflect rises and falls in neural activity. When the volunteers viewed

images of human bodies and nonfacial body parts, a small piece of visual cortex

responded much more vigorously than when they viewed images of various nonhuman

and inanimate objects, Downing’s group reports in the Sept. 28 Science.

The findings held regardless of whether participants saw photographs, drawings,

stick figures, or silhouettes of human bodies and body parts. Pictures of either

nonhuman mammals or scrambled versions of human stick figures and silhouettes

elicited a modest activity boost in the proposed body-processing area of the

brain. Activation of the same tissue was lower during displays of fish and other

animals and weaker still for objects such as scissors and screwdriver handles.

Some neuroscientists doubt that separate chunks of the brain are hardwired to

respond only to specific categories of objects (SN: 7/7/01, p. 10: Faces of Perception). The visual

features that make up all sorts of objects draw to some extent on shared territory

in the brain, concludes a separate brain-scanning team led by James V. Haxby of

the National Institute of Mental Health in Bethesda, Md., in another report in the

same issue of Science.

As volunteers view faces, houses, cats, bottles, scissors, shoes, chairs, and

abstract images, the patterns of activity for each overlap in the visual cortex,

Haxby says. In his view, these neural patterns represent perceptions of different

categories of items forged out of their partially shared visual elements.

Isabel Gauthier of Vanderbilt University in Nashville suspects that specific brain

regions solve problems that transcend any one category. Her studies suggest, for

example, that the brain’s proposed face-processing area actually analyzes the

visual characteristics of any class of objects–such as classic cars or bird

species–that a person comes to know extremely well.

The body-processing center studied by Downing’s team also reacts strongly when

volunteers watch groups of dots made to move so that they simulate the motion of a

living thing, Gauthier says. This region may decipher any nearby movements, which

often involve other human bodies, she speculates.

In a concise summary of the research in this area, Michael J. Tarr of Brown

University in Providence, R.I., notes that “there’s no definitive answer at this

point to how object recognition works in the brain.”

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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