Sensory brain regions may drive speech relearning more than motor regions, with new research linking them to memory for newly learned speech movements.
The findings challenge the assumption that speech motor learning and the memory of newly learned speech movements are primarily driven by motor regions of the brain.
The study, published in the Proceedings of the National Academy of Sciences, was led by Nishant Rao, associate research scientist, and David Ostry, professor adjunct, both of the Yale University Child Study Center.
“These findings establish a sensory basis for speech motor memory, indicating that plasticity in sensory brain areas is necessary for learning and retaining newly acquired speech movements,” Rao said.
Learning a new language or relearning speech after a stroke depends on coordinated movements controlled by brain networks.
These include the orofacial sensory system, which processes touch and position from the lips, tongue, jaw and face, and the motor system, which sends signals that move muscles in the right way at the right time.
The findings indicate that retaining newly learned speech movements depends primarily on sensory brain processes rather than motor learning.
The results also suggest speech-processing and recognition technologies could improve by more explicitly integrating auditory and somatic sensory signals.
The work has implications for rehabilitation and new neurological technologies, suggesting the sensory cortex as a possible target for rehabilitation after a stroke or brain injury that affects speech.
The findings may also help improve brain-computer interfaces by showing the importance of sensory cortical activity for movement control.
Rao, Ostry and their team used an experimental model in which participants’ speech was changed in real time and played back to them through headphones, leading to speech motor learning.
They applied transcranial magnetic stimulation, or TMS, a non-invasive technique that can temporarily disrupt neural activity, to one of three important speech-related regions: the auditory cortex, the somatosensory cortex, or the motor cortex.
The researchers checked how well participants remembered their learning 24 hours later.
Disrupting activity in the sensory cortex, either auditory or somatosensory, made it harder for participants to keep new speech changes, but disrupting the motor cortex did not have this effect.
“Our study challenges the assumption that new speech memories are solely reliant on changes in motor areas of the brain,” Rao said.
“Instead, it underscores the importance of changes in auditory and somatosensory brain areas in shaping how we learn to speak.”
“Sensorimotor neuroscience has traditionally focused on frontal motor areas as the principal drivers of movement,” Ostry said.
“This study changes that understanding by showing that human motor learning is extensively sensory in nature.”
Study reveals how spinal cord injury disrupts breastfeeding
