Tracking the brain's language streams.

Experiments conducted with three brain-damaged men indicate that interconnected groups of neurons in the brain function as separate "information processing streams" that handle either nouns or verbs, as well as the general concepts underlying these building blocks of language, according to a new report.

Certain brain structures link areas of conceptual knowledge (such as the traits, sounds, and movements associated with birds) to regions stocked with corresponding nouns or verbs (for example, duck, ostrich, and other bird names), assert Antonio R. Damasio and Daniel Tranel, neurologists at the University of lowa College of Medicine in Iowa City.

This set-up spreads out word and conceptual knowledge in neural networks that, under some circumstances, still process language following partial brain damage, the investigators hold. Other researchers have noted selective impairment of verbs in two brain-damaged women (SN: 3/2/91, p. 134).

When presented with pictures of various activities, two of the men studied by Damasio and Tranel named or wrote verbs that correctly described most of the depictions, as did 10 healthy controls. However, in a similar task designed to elicit nouns, the same two men performed far worse than controls, the scientists report in the June 1 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES. Proper nouns, evoked by pictures of family, friends, and famous people, caused the men more difficulty than common nouns, tested with pictures of animals, fruits, vegetables, and tools.

Yet other language abilities remained normal, including reading and writing. They often recalled the same nouns that had eluded them on the initial naming test if an experimenter presented the first syllable of the troublesome word. And their routine conversations often included the same problem nouns.

The third man showed the opposite pattern, identifying most common and proper nouns portrayed in pictures but often failing to come up with descriptive verbs.

The first two men share damage to the same part of the brains left hemisphere, which lies outside so-called language areas, the researchers note. This region apparently links language structures devoted to nouns with parts of the brain that interpret the various characteristics of an entity, they argue; when the link breaks down, so does noun retrieval.

The third man experienced damage to a different part of the left hemisphere, which may mediate between verb-specific language and conceptual areas, Damasio and Tranel maintain.