Secrets of Human Speech Uncovered
Work at UCSF Shows Brain Exerts Symphony-Like Control of Vocal Tract During the Act of Speaking
A team of researchers at UC San Francisco has uncovered the neurological basis of speech motor control, the complex coordinated activity of tiny brain regions that controls our lips, jaw, tongue and larynx as we speak.
Described this week 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. It also sheds light on an ability that is unique to humans among living creatures but poorly understood.
“Speaking is so fundamental to who we are as humans - nearly all of us learn to speak,” said senior author Edward Chang, MD, a neurosurgeon at the UCSF Epilepsy Center and a faculty member in the UCSF Center for Integrative Neuroscience. “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.
To understand how speech articulation works, 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.