Brains hammer home categorical knowledge.

A hit song from about 30 years ago was titled "The Windmills of Your Mind."

Results of a new scientific study may inspire a sequel to that tune: "The Pigs and Pliers of Your Brain."

Scientists at the National Institute of Mental Health in Bethesda, Md., have found that knowledge about the names of animals and tools-two broad categories of objects-gets handled by largely separate networks of brain regions. The organization of these networks reflects, at least in part, cerebral recognition of unique properties associated with items in each category, the investigators contend in the Feb. 15 Nature.

That means, for instance, that when volunteers silently name animal pictures, strong responses occur in early visual processing areas that help sort out subtle differences in appearance. When people silently name pictures of tools, activity rises markedly in two patches of brain tissue that had previously been implicated in imagined hand movements and the generation of action words (such as saying "write" when shown a picture of a pencil).

"We think that when you see an object, brain networks are automatically activated that contain verbal knowledge about that object's attributes and uses," asserts study director Alex Martin. "This allows the object to be categorized."

Until now, isolated cases of people with brain damage have provided most of the evidence of specialized neural circuits devoted to categorical knowledge.

Some of these people find themselves unable to name living things; others draw a blank when shown man-made objects.

Martin's group used positron emission tomography (PET) scans to identify brain areas associated with the silent naming of common animals and tools by eight men and eight women, all neurologically healthy. The data charted increases and decreases in blood flow throughout the brain during these tasks. The technique provided an indirect look at whether particular brain regions worked harder or eased up during the tasks.

The researchers also compared the data to PET scans showing brain activity stimulated when participants viewed fuzzy images similar to a television test pattern and a series of nonsense objects with no discernible use.

Naming both animals and tools boosted activity in a part of the temporal lobe that deciphers visual forms. The two tasks also yielded comparable blood-flow surges in a frontal brain area linked to speech and grammar use.

From that common foundation, the activity in response to animal and tool pictures spread through the brain in different directions, Martin and his coworkers hold. Animal pictures triggered cellular exertion in a visual area that aids in distinguishing, for example, a leopard's spotted coat from a lion's shaggy mane. Tools generated activity in two areas that identify how and for what purposes implements get used, the scientists maintain.

Martin's group also presented PET data in the Oct. 6, 1995 Science pointing to the existence of separate brain systems for knowledge about the colors and uses of objects.

Further brain-scan evidence on verbal and other knowledge of certain categories of objects, obtained by researchers at the University of Iowa College of Medicine in Iowa City, is slated for publication later this year.