Language centers in the brains of rhesus macaques light up when the monkeys hear calls and screams from fellow monkeys, researchers said in a study that suggests language skills evolved early in primates.
Researchers who scanned the brains of monkeys while playing them various sounds found the animals used the same areas of the brain when they heard monkey calls as humans do when listening to speech.
Writing in this week's issue of the journal Nature Neuroscience, the international team of researchers said this finding suggests that early ancestors of humans possessed the brain structures needed for language before they developed language itself.
"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 Battey, director of the National Institute on Deafness and Other Communication Disorders, which helped conduct the study.
"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."
The NIDCD's Allen Braun and colleagues trained rhesus monkeys to sit quietly in PET scanners. Positron emission tomography detects active cells and can be used to see which parts of the brain are working.
They played coos and screams made by rhesus monkeys that the test animals did not know, as well as "nonbiological sounds" such as music and computer-generated noises.
The monkey sounds activated areas of the brain corresponding to those used by humans in processing language — known as Broca's area, and Wernicke's area, the researchers said.
In contrast, music and computer sounds mostly activated the brain's primary auditory areas.
"This finding suggests the possibility that the last common ancestor of macaques and humans, which lived 25 to 30 million years ago, possessed key neural mechanisms (that may have been used) ... during the evolution of language," the researchers wrote.
"Although monkeys do not have language, they do possess a repertoire of species-specific vocalizations that — like human speech — seem to encode meaning in arbitrary sound patterns."
For instance, many species of monkeys have calls to warn of danger from above, such as an eagle, calls referring specifically to leopards and also have various sounds used while socializing.
