Author: Shahabeddin Vahdat

Publisher:

Published: 2013

Total Pages:

ISBN-13:

"Research on plasticity in motor systems has for the most part developed separately from work on sensory plasticity, as if training-induced changes to the brain affected each of these systems in isolation. The aim of this thesis is to explore the association between the sensory and motor systems when a new skill is acquired. The experiments reported in this dissertation systematically examine two hypotheses about neuroplasticity: (i) that motor learning changes perceptual function and the function of somatosensory areas of the brain, and (ii) that somatosensory training changes both motor function and motor areas of the brain. The first study aimed at providing a unified approach to test the first hypothesis. We combined both psychophysical and neuroimaging procedures to examine the connection between changes in the behavior and brain as a result of motor learning. We used a dynamics adaptation task as a model of motor learning in conjunction with somatosensory discrimination of the limb's movement direction which permits quantification of perceptual changes that occurs in conjunction with motor learning. We used functional magnetic resonance imaging (fMRI) to calculate measures of functional connectivity during resting-state periods following learning. This technique allowed us to study longer lasting plasticity in the sensorimotor system, during the period in which the motor memory is being consolidated. We developed a new hypothesis-driven technique which enables us to incorporate psychophysical measures in functional connectivity analysis to identify behaviorally-related neuroplasticity as a result of learning. Using this technique, we identified a new network in motor learning involving second somatosensory cortex, ventral premotor cortex and supplementary motor area whose activation is specifically related to perceptual changes that occur in conjunction with motor learning. Subjects who showed greater change in functional connectivity within this network, also showed a greater change in perceptual function. In study two, we proposed and implemented a new analytic data-driven method based on independent component analysis (ICA), which enabled us to systematically extract and classify shared and condition-specific networks corresponding to the pre-learning and post-learning conditions. The proposed algorithm was specifically designed to solve the problems of the regular ICA approach in conducting between-condition comparisons. Using this method we identified a specific network corresponding to the post-learning condition comprising clusters in contralateral superior parietal lobule, second somatosensory cortex, premotor cortex, and supplementary motor area. The third study was aimed at testing the second hypothesis described above. Using similar procedures and techniques to those used in the first study, we found that somatosensory discrimination training combined with periods of passive movement as short as 45 minutes increased functional connectivity between sensory and motor areas of the brain and, importantly, in motor areas alone. In behavioral terms, somatosensory training facilitates motor learning. Improvements were seen in both the rate and extent of learning and they persisted for at least one day. Sensory repetition without perceptual learning was less able to induce plasticity in the motor system. This suggests that somatosensory training can induce reorganization in the motor system and benefits from cognitive involvement and skill acquisition in the sensory domain. Overall, our studies point to a unified model of sensorimotor plasticity in which the effects of learning are not local to either sensory or motor systems, but rather each has effects that spread into functionally related areas of the brain beyond the base modality." --