This project involves studies of speech motor learning and speech perceptual function that focus on plasticity in the somatosensory system. The studies in Aim 1 test the hypothesis that the somatosensory system contributes to changes to the brain?s sensorimotor network over the course of speech motor learning. These studies use a robotic device that selectively alters somatosensory input during speech and measures subjects? adaptive responses to this mechanical perturbation. This technique is combined with a new resting-state neuroimaging analysis that identifies from among the set of areas that encode learning those whose functional connectivity is both strengthened with learning and are not a by-product of activity elsewhere in the network. Our preliminary results suggest that somatosensory system contributes to extensive changes to the brain?s sensorimotor network over the course of speech motor learning.
Aim 2 will test the idea that speech motor adaptation relies on sensory working memory (auditory and somatosensory) and that individual differences in working memory predict adaptation. We will transiently suppress activity in a region of pre-frontal cortex associated with auditory and somatic working memory, using continuous theta- burst trans-cranial magnetic stimulation, to test its involvement in speech motor learning.
Aim 3 tests the hypothesis that somatosensory inputs comparable to those normally associated with speech production alter the perception of speech sounds and reveal the presence of a somatic cortical network that participates in speech perception. We have developed an MR compatible robotic device that delivers speech-like patterns of facial skin deformation as participants listen to speech sounds in the scanner. We will use this technique to test the idea that repeated pairing of auditory and somatosensory inputs, as would occur in speech motor learning, serves to engage somatosensory areas of the brain in speech perception.
Speech motor learning relies on the neural control of the orofacial motor apparatus and additionally on both the auditory input that results from the sounds that are produced as we speak and also the somatosensory inputs that originate in the muscles and soft tissues of the vocal tract. Sensory and motor function occur simultaneously and as a result it is difficult to separate elements of learning that are attributable to each individual system. We have designed a series of experiments that focus on plasticity in the somatosensory system in speech motor adaptation and use a combination of behavioral, neuroimaging and neurophysiological techniques. Aim 1 focuses on the brain networks that play a central role in adaptation. The studies utilize a partial correlation statistical technique that enables us to identify changes in functional brain networks following learning that are not explained by activity in other areas that are active in speech perception and production. A second set of studies tests the idea that a working memory circuit involving prefrontal cortex contributes to speech motor adaptation. A final series of studies use an MRI compatible robotic device that delivers speech-like patterns of somatosensory input as participants listen to speech sounds in the scanner. We will use this technique to test the idea that repeated pairing of auditory and somatosensory inputs, as would occur in speech motor learning, serves to engage somatosensory areas of the brain in speech perception.
