A study by researchers at McGill University and Yale School of Medicine suggests that learning—and later retaining—new speech patterns depends more on brain areas that process sound and bodily sensation than on the motor cortex regions that control speech movements. The work was published in the Proceedings of the National Academy of Sciences.
The findings challenge a common assumption in sensorimotor neuroscience: that long-term speech learning and its consolidation are driven primarily by motor cortex changes.
In the experiments, researchers altered participants’ speech feedback in real time and then used transcranial magnetic stimulation (TMS) to temporarily disrupt activity in three regions implicated in speech production and learning: the auditory cortex, the somatosensory cortex and the motor cortex.
When stimulation targeted the auditory or somatosensory cortex, participants showed poorer retention of the newly learned speech movements when tested 24 hours later. Disrupting the motor cortex, by contrast, had little effect on retention.
"Sensorimotor neuroscience has traditionally focused on frontal motor areas as the principal drivers of movement. This study changes that understanding by showing that human speech learning is extensively sensory in nature," said David Ostry, a professor of psychology at McGill University.
"Our study challenges the assumption that new speech memories are solely reliant on changes in motor areas of the brain. Instead, it underscores the importance of changes in auditory and somatosensory brain areas in shaping how we learn to speak," said study co-author Nishant Rao, an associate research scientist at Yale University.
The researchers said the results could help guide future work on speech rehabilitation—such as recovery after stroke—and may also inform the design of brain-based communication and speech technologies that incorporate sensory processing.
The study, titled “Sensory basis of speech motor learning and memory,” was authored by Nishant Rao, Rosalie Gendron, Timothy F. Manning and David J. Ostry. It reported support from the U.S. National Institute on Deafness and Other Communication Disorders.
