A study, published today in the prestigious journal Nature by Dr. Michael Petrides and colleagues at the Montreal Neurological Institute (MNI) at McGill University, challenges current thinking that speech developed as a result of new structures that evolved in the human brain. Dr. Petrides and colleagues have identified a distinct brain region that controls jaw movements in macaque monkeys that is comparable to Broca's area - the region in the human brain critical for speech production. This discovery is important as it suggests that this area of the brain evolved originally to perform high-order control over the mouth and the jaw, and that as humans evolved this area came to control the movements necessary for speech.
"Our study shows that nonlinguistic monkeys possess an area comparable to Broca's area ?it is located in the same region and has the same anatomical characteristics as Broca's area in the human brain", explained Dr. Michael Petrides, Coordinator of the Cognitive Neuroscience Unit at the MNI and Professor in the Department of Neurology and Neurosurgery, McGill University.
"The researchers performed quantitative microscopic analysis of the cytoarchitecture of the region of interest and electrophysiological stimulation and recording within this region.
When this area in the monkey was electrically stimulated, oral and facial motor responses were evoked ?such as jaw movement sequences, as well as respiratory responses. In addition, Broca's area is connected with a region of the brain immediately in front of it that is involved in the retrieval of information from memory.
"These connections suggest to us that Broca's area is in a unique position to use information shared from past experience and which is stored in memory for the service of communicative acts," explains Dr. Petrides. "That is, Broca's area may have evolved originally as an area exercising high-level control over oral and facial actions, including those related
to communicative acts, and that, in the human brain, this area eventually came to control also certain aspects of the speech act."
The researchers hope that future studies of the anatomy and physiology of this region will yield major new insights as to why Broca's area became involved with speech in the human brain.
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