Washington:  Scientists have finally decoded the human act of speaking and the complex coordinated activity of tiny brain regions that control our lips, jaws, tongue and larynx as we speak.

Researchers at the University of California-San Francisco show how brain exerts symphony-like control of vocal tract during the act of speaking.

Published in the journal Nature, the work has potential implications for developing computer-brain interfaces for artificial speech communication and for the treatment of speech disorders.

"Speaking is so fundamental to who we are as humans – nearly all of us learn to speak," senior author Edward Chang, a neurosurgeon at the UCSF Epilepsy Center and a faculty member in the UCSF Center for Integrative Neuroscience said.

"But it's probably the most complex motor activity we do."

The complexity comes from the fact that spoken words require the coordinated efforts of numerous "articulators" in the vocal tract – the lips, tongue, jaw and larynx – but scientists have not understood how the movements of these distinct articulators are precisely coordinated in the brain.

For the study, Chang and his colleagues recorded electrical activity directly from the brains of three people undergoing brain surgery at UCSF, and used this information to determine the spatial organization of the "speech sensorimotor cortex," which controls the lips, tongue, jaw, larynx as a person speaks.

This gave them a map of which parts of the brain control which parts of the vocal tract.

They then applied a sophisticated new method called "state-space" analysis to observe the complex spatial and temporal patterns of neural activity in the speech sensorimotor cortex that play out as someone speaks.

This revealed a surprising sophistication in how the brain's speech sensorimotor cortex works.

It was found that this cortical area has a hierarchical and cyclical structure that exerts a split-second, symphony-like control over the tongue, jaw, larynx and lips.

"These properties may reflect cortical strategies to greatly simplify the complex coordination of articulators in fluent speech," co-author of the study Kristofer Bouchard said.

The patients involved in the study were all at UCSF undergoing surgery for severe, untreatable epilepsy.


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