Researchers Identify Region in Monkey’s Brain that Parallels Human Brain Area Tied to Speech
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RESEARCHERS IDENTIFY REGION IN MONKEY’S BRAIN THAT PARALLELS HUMAN BRAIN AREA TIED TO SPEECH
WASHINGTON, DC June 28, 2005 – New research contradicts the notion that speech developed as a result of novel structures that evolved in the human brain. Researchers have now identified a distinct brain region that controls jaw movements in macaque monkeys whose location and microscopic structure is the same as an area often referred to as Broca’s area, which is crucial for speech production in the human brain.
The finding may turn conventional thinking about the evolution of speech on its head. “A homology between a monkey motor area and the human speech area is a spectacular finding,” says Michael Goldberg, MD, a professor of cognitive and systems neurobiology at Columbia University.
Following detailed comparative study showing similarities in microscopic brain structures in humans and macaques, Michael Petrides, PhD, and his team at McGill University in Montreal confirmed their initial findings by recording neuronal activity in the newly described area when they touched the monkeys’ mouths. They also were able to evoke jaw movements by stimulating that part of the monkey brain. The study appears in the June 30 issue of Nature.
“The presence of Broca’s area in the nonlinguistic monkey brain implies that language is a byproduct of the growth, over millions of years, of the primate brain,” Petrides said. “As associated cerebral cortical areas expanded, the pre-existing cellular structures found in Broca’s area were able to take advantage of the massive upgrade of the brain’s computational power.”
Scientists see the discovery of a homologue of Broca’s area in the monkey brain as a boon to speech and language research. The question now, says UC Davis neurology professor and VA Martinez Aphasia Center director Nina Dronkers, PhD, is: Did this structurally distinct area “evolve in humans to control the movements that are unique to speech, or is it still just controlling the orofacial musculature on which speech movements are dependent?
“We don't yet know the answer to this question,” Dronkers says. “But the Petrides study brings us closer to understanding the biological foundations of speech.”
Petrides is a member of the Society for Neuroscience, an organization of more than 36,000 basic scientists and clinicians who study the brain and nervous system. He may be contacted at: Petrides@ego.psych.mcgill.ca