Dissertation Defense: Rachael Harrington
Candidate Name: Rachael Harrington
Thesis Advisor: Michelle L. Harris-Love, Ph.D.
Thesis Advisor: Peter E. Turkeltaub, M.D./Ph.D.
Title: Mechanisms of Recovery in Patients with Severe Arm Impairment After Stroke
Background: Arm hemiparesis is a common attribute of stroke. Patients with more severe arm impairment demonstrate nonlesioned hemisphere activation during brain imaging of motor function. Determining lesion characteristic differences between patients with mild and severe arm impairment may help to explain this activation. To better plan intervention strategies, it is necessary to understand if nonlesioned hemisphere activation is contributing to movement.
Objective: The objectives of this project were to explore which lesion characteristics result in severe arm impairment and to determine the contribution of the nonlesioned hemisphere to reaching function in these patients, specifically the contribution of the nonlesioned dorsal premotor cortex (PMd).
Methods: Lesion characteristics were mapped and compared between a group of patients with mild and severe arm impairment. Lesion location was compared to various aspects of reaching movement. During a reaching task, online double-pulse transcranial magnetic stimulation (DP-TMS) was applied to lesioned and nonlesioned primary motor cortex (M1) and PMd in patients with mild and severe arm impairment and to nonlesioned M1 and PMd in a larger group of patients with severe impairment to measure changes in movement time and reaching kinematics.
Results: A significantly larger percentage of patients with severe arm impairment had lesions involving the posterior limb of the internal capsule (PLIC) and patients with lesions in PLIC had significantly worse reaching performance. There was no significant main effect for patients with mild or severe impairment after perturbation of the lesioned hemisphere, however, patients with severe impairment demonstrated a significant change in movement time after perturbation of the nonlesioned hemisphere and this effect was greatest after DP-TMS to PMd. In patients with severe impairment, only DP-TMS to PMd, and not to either control site, resulted in a change in movement time in the nonlesioned hemisphere.
Summary: Overall, this study demonstrates that some patients with severe, chronic impairment have sites within the nonlesioned hemisphere that can contribute to post-stroke movement and it may be possible to identify these patients by examining their lesion characteristics. Future research into non-invasive brain stimulation as a method to improve the efficiency of intervention after stroke should consider nonlesioned PMd as a potential site for upregulation in this group of patients.
Tuesday, April 18, 2017 at 10:00am to 12:00pm
Building D, Warwick Evans Room
4000 Reservoir Road, N.W., Washington