PET shows evolution of human language

A rhesus monkey, or macaque, contemplating the coos and screams of a fellow rhesus makes use of brain regions that correspond to the two principal language centers in the human brain: Broca's area and Wernicke's area.

The finding bolsters the hypothesis that the last common ancestor of macaques and humans, which lived 25 to 30 million years ago, possessed key neural mechanisms instrumental for language evolution.

Dr. Allen Braun, a researcher at the National Institute on Deafness and Other Communication Disorders (NIDCD), and colleagues used oxygen-15 PET to measure brain activity in three macaques as they listened to monkey coos and screams, as well as acoustically similar nonbiological sounds (Nat Neurosci 2006;9;1064-1070).

The coos and screams, although acoustically different from each other, activated brain regions -the ventral premotor cortex, temporoparietal area, and posterior parietal cortex - that correspond to Broca's and Wernicke's areas.

In contrast, the nonbiological sounds, which were acoustically similar to the coos and screams but had no meaning for the animals, elicited significantly less activity in these regions.

"This intriguing finding brings us closer to understanding the point at which the building blocks of language appeared on the evolutionary timeline," said Dr. James F. Battey Jr., director of the NIDCD. "While the fossil record cannot answer this question for us, we can turn to the here and now - through brain imaging of living nonhuman primates - for a glimpse into how language, or at least the neural circuitry required for language, came to be."

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