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"The Effects of Visuomotor Discordance on Motor Cortex Excitability:
Implications for Stroke Rehabilitation"

by
Hamid F. Bagce
M.D./Ph.D. Program
B.S. 2007, New Jersey Institute of Technology



Thesis Advisor: Eugene Tunik, Ph.D., PT
Assistant Professor
Department of Rehabilitation and Movement Science

Wednesday, May 16, 2012
10:00 A. M., Stanley S. Bergen Building, Dean’s Conference Room, Room 133


Abstract

Reconciling discrepancy between intended actions and visual feedback (“visuomotor discordance”) is integral for motor function. Recent studies have shown that motor memory formation, including acquisition, consolidation, and retention, is partially encoded in primary motor cortex (M1). However, a precise mechanism for M1’s role during motor learning remains unknown, as prior studies have not controlled for performance- or error-related changes in excitability following visuomotor adaptation. In the first study of this project, I set out to identify the neural correlates of motor memory formation in M1 following adaptation to a visuomotor gain in a novel virtual reality (VR) environment. Controlling for all possible kinematic and electrophysiological confounds (effectively “clamping” these variables), I demonstrate learning-related (not performance- or error-related) increases in M1 excitability for a period of time outlasting visuomotor gain adaptation in healthy subjects. These increases are sign-independent (independent of whether visual discordance is gain-up or gain-down) and muscle-specific (focused on the area of M1 controlling the agonist muscle performing the movement task). In a subsequent study I demonstrate similar excitability increases in a group of patients with chronic stroke, although expectedly stroke patients (compared to healthy subjects) were slower to learn and exhibited less-robust excitability increases. In the final study of this project I demonstrate that two weeks (rather than a single session) of intense training with visuomotor discordance in a VR environment induces significant neuroplastic changes in sensorimotor cortex. Specifically, VR therapy reorganizes corticospinal excitability to a more confined region of ipsilesional sensorimotor cortex, simulating the focal activation pattern normally observed in healthy subject populations. As a result, visuomotor discordance may be a useful tool in designing effective VR training protocols for patients with neurological and neuromuscular diseases such as stroke, allowing patients to regain pre-stroke neural excitability patterns and thereby facilitating functional recovery.


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