Similarities Found In Human, Chimp Brains
Columbia, Mount Sinai Scientists Find Region That Controls Language Identical in Both Species; Chimps May Use Gestures to Communicate
Researchers at Mount Sinai School of Medicine, Columbia University and the National Institutes of Health have found that a region of the brain thought to control language is proportionately the same size in humans and chimpanzees, disproving a theory that the brain section was enlarged only in humans.
The discovery, reported in the Jan. 9 issue of the journal Science, throws into question the role of the planum temporale, a part of the brain's temporal cortex that is located beneath the parietal cortex. The planum temporale of the left hemisphere is normally larger than in the right hemisphere in humans, but 94 percent of the chimpanzee brains studied demonstrated the same asymmetry.
Could the research result be interpreted to mean that chimpanzees have some kind of language? "I don't think they have a language, but I do agree that they have some kind of communication system that might be more complex than we have heretofore thought," said Ralph Holloway, professor of anthropology at Columbia and co-author of the Science paper. He believes chimps may converse using a sophisticated array of facial, body and hand gestures, perhaps augmented with grunting or other vocalizations.
Patrick Gannon, assistant professor and director of the Paleoneurology Research Laboratory in the Department of Otolaryngology at Mount Sinai, first suspected that chimpanzee brains might show the same asymmetry as those of humans. He sought the collaboration of Professor Holloway, who then assisted in measuring the planum temporale, which is not an obvious anatomical feature, on his collection of 18 chimpanzee brains. The Columbia anthropologist conducts comparative neuroanatomical studies on the chimpanzee brains in order to better understand evolution of the human brain.
The research finding contradicts a long-standing scientific theory that only humans displayed the left-side brain enlargement. Nineteenth-century neurologist Carl Wernicke had noticed that patients with brain lesions of the posterior temporal lobe and parietal lobe - the same area studied by the Mount Sinai and Columbia researchers - could produce language but couldn't understand it. That region of the temporal cortex, also known as Wernicke's area, was thought to control language comprehension, but only in humans.
"After 100 years of people doing comparative brain studies, you assume that the dogma is true. It came as quite a shock to discover that the chimpanzee brains did show the same asymmetry as humans," Dr. Gannon said.
He first theorized that the received wisdom might not be true when he conducted magnetic resonance imaging studies of chimpanzee brains in an NIH study and noticed the discrepancy between the brain hemispheres.
The authors of the paper, who also included Allen Braun of the National Institute on Deafness and Other Communication Disorders at NIH, proposed several possible interpretations of the work, in addition to the possibility of chimp communication. If both chimps and humans have an enlarged planum temporale, their common ancestor probably had the feature as well, though the brain region may not have acquired its language functions until humans split off from other primates 6 to 8 million years ago. Finally, it may well be that the planum temporale is not involved in language in either chimps or humans.
The research was supported by the National Science Foundation, the National Institute on Deafness and Other Communication Disorders of the National Institutes of Health and the Department of Otolaryngology and the Grabscheid Voice Center at Mount Sinai.