Somatosensory Basis of Human Motor Learning

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The long term goal of my research is to understand how the human central nervous system produces voluntary movement and motor learning. The goal of the research program described here is to test the idea that motor learning involves not only changes to motor behaviour and motor areas of the brain, but incorporates changes in somatosensory function and somatosensory neural processing as well. Motor learning changes not only how we move but how we process and perceive our own movements. The 5-yr objectives are (1) to test the idea that somatosensory perception changes in systematic ways when we learn to interact with objects in the environment, and (2) to test the neural basis of these effects in somatosensory and motor brain areas. We will test the idea that learning-based somatosensory changes will depend on whether an object is a target (something to be reached) or an obstacle. We will test the hypothesis that sensed hand position will shift away from an object when it is an obstacle, and towards targets, compared to when there is no object. We will test the idea that somatosensory acuity will be greater near obstacles, and less near targets. Interestingly, in speech perception, listeners are less sentitive to acoustic differences in vowels that sit close to a vowel prototype (a speech target) compared to those that sit farther away from the prototype (the perceptual magnet effect). This raises the interesting possibility that warping of perceptual space is a general phenomenon associated with skilled motor behaviour. We will also test the cortical and segmental (spinal) contributions to somatosensory change accompanying motor learning. We will use repetitive transcranial magnetic stimulation (rTMS) to probe the role of several cortical areas involved in somatosensation, action and motor learning, before and after motor learning, including primary somatosensory cortical areas SI and SII, supplementary motor area (SMA), dorsal and ventral premotor cortices PMd and PMv, and parietal cortical areas. To assess the potential role of segmental reflex modulation we will use an H-reflex paradigm to assess changes in reflex excitability before vs after motor learning, and how those changes correlate with changes in sensed limb position. In summary, there is accumulating evidence from behavioral, neurophysiological, and neuroimaging studies that the acquisition of motor skills involves both perceptual and motor learning. Motor learning changes perceptual function and the sensory circuits of the brain. This points to a new theoretical approach to motor learning in which perceptual learning and sensory plasticity play a fundamental role. A better understanding of the sensory as well as motor determinants of motor skill learning could lead to better brain-machine interfaces such as neuro-prosthetic arms, as well as new approaches to building anthropomorphic robots with biologically-inspired control.