Language Center Similarities in the Brains of Humans and Chimps

An area of the brain that controls language (the planum temporale), and has long been designated as unique to humans, is revealed to have remarkable similarities to that of the same area in chimpanzees. A new study in the January 9, 1998, issue of Science reports the results of careful measurement techniques that compared this area in both species with significant and promising results.

"Not only are the areas similar in structure and appearance, but the area in the left brain of chimpanzees is consistently larger and more developed than the right. Just as in humans," said investigator Allen R. Braun, M.D., of the National Institute on Deafness and Other Communication Disorders (NIDCD) of the National Institutes of Health.

The marked differences in the two sides of the chimp brain were first observed during a magnetic resonance imaging study that was conducted by two of the authors. Following that discovery, this research team, led by anthropologist Patrick J. Gannon, Ph.D., of the Mount Sinai School of Medicine, made surface measurements of the planum temporale of 18 chimpanzee brains that were obtained from several archived collections. The anatomical markers of the region were identified and found to be similar to those of humans. The investigators then precisely measured both the right and left sides of the brain. In 94 percent, or 17 of the 18 brains, the left side was significantly larger than the right.

The predominance of this area of the left brain has long been felt to be unique to humans, subserving functions such as language, handedness and the development of musical talent. The authors suggest that their results bring the concept of human uniqueness into question and in addition, raise new questions. For example, have chimps developed this same area for another, yet unidentified, function? Is it just by chance that humans developed this area for language? Do chimps and humans share a common neurological substrate for language? Have chimpanzees developed this area for a subtle but sophisticated form of gestural communication that has not yet been identified by humans?

"These results also raise the possibility of developing an animal model for conditions such as dyslexia and schizophrenia, which are predominantly disorders of the left temporal lobe of the brain," noted Dr. Gannon.

"This study will generate language research from a new perspective," commented James F. Battey, Jr., M.D., Ph.D., Acting Director of the NIDCD.

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