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"New insights into human M1 function: Visuomotor adaptation and mapping hand representation"

by
Mathew Benjamin Yarossi
Biomedical Engineering Program
B.S. 2004, Northwestern University, Evanston, IL
M.S. 2011, New Jersey Institute of Technology, Newark, NJ


Thesis Advisor: Eugene Tunik, Ph.D. P.T.
Associate Professor
Rehabilitation and Movement Science

Thursday, August 10, 2017
1:00 P.M., SSB Room 921


Abstract

Hand dexterity is essential to daily function, is very frequently lost to some degree after stroke, and is particularly hard to rehabilitate. Despite visionís strong modulatory influence over the brain, its potential in stroke rehabilitation is relatively unexplored. The overall goal of this project was to systematically test in healthy subjects the neurophysiological basis for learning visuomotor gain and mirror discordance, and test in acute stroke patients how training involving these visual feedback manipulations can improve function, and influence motor cortex (M1) reorganization. We hypothesized that visuomotor discordance can be used to selectively modulate M1 excitability in healthy persons and that an intervention involving the use of visuomotor discordance will influence M1 reorganization and recovery following stroke.
To assess the neurophysiological mechanisms underlying M1 modulation in response to visuomotor discordance we used transcranial magnetic stimulation (TMS) to measure corticospinal excitability and quantitative biomechanics to measure behavior. The role of M1 in the learning, retention and savings of a visuomotor gain was studied by systematically varying feedback during unlearning to influence behavior during relearning. Data indicate increased excitability upon re-exposure to visual motor gain discordance is related to savings, and not residual adaptation or performance. In a second experiment, the effect of mirror visual feedback on ipsilateral M1 excitability was assessed using the same measures of neurophysiology and behavior. Data demonstrate that the ipsilateral M1 response was greatest when individuals perform target directed movements under mirror feedback. Furthermore, using paired pulse TMS techniques, data indicate that mirror feedback induced ipsilateral excitability is associated with interhemispheric parietal-M1 modulation.
Hand rehabilitation involving virtual reality to induce discordant visual feedback was tested in individuals with hemiplegia due to acute stroke. Participants underwent two weeks of treatment and reorganization of M1 was assessed using TMS to map cortical topography. Improvement in clinical and kinematic measures was associated with expansion of the lesioned hemisphere excitable cortical territory for intrinsic hand muscles.
Collectively, the work presented here provides evidence that altered visual feedback of voluntary movements modulates M1 excitability, and may be efficacious for rehabilitation of hand function following stroke.


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