Somatosensory Basis of Speech Motor Learning

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The overall goal of my research is to understand plasticity in both sensory and motor areas of the brain and its contribution to human motor learning. My research uses both speech motor learning and human limb movement as experimental models. The studies described in this proposal focus on speech and specifically on the role of plasticity in the somatosensory system in both speech motor learning and speech perception. 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 for this purpose 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.