Document Type

Dissertation

Date of Award

5-31-2019

Degree Name

Doctor of Philosophy in Biomedical Engineering - (Ph.D.)

Department

Biomedical Engineering

First Advisor

Sergei Adamovich

Second Advisor

Antje Ihlefeld

Third Advisor

Carrie Esopenko

Fourth Advisor

Mesut Sahin

Fifth Advisor

Gerard G. Fluet

Abstract

Stroke is the leading cause of disability in the United States (American Heart Association, American Stroke Association) affecting 800,000 individuals annually (i.e., one person every 45 seconds). Therapy for stroke often uses repetitive task practice, which is difficult to perform for patients due to impairment. Mirror visual feedback (MVF) based rehabilitation uses the effect of observing the mirror reflection of volitional movement of one limb, to activate visuomotor brain areas that process movement of the opposite limb. In persons with hemiplegia due to stroke, exercising the less affected limb while observing its reflection, perceived by them as the motion of the paralyzed limb, have been linked to positive rehabilitation outcomes. However, the neural mechanisms underlying MVF are poorly understood, and the rehabilitation outcomes of these studies vary greatly, with one possible source of variability being the type of sensorimotor motor task that is used with MVF.

In this dissertation Transcranial Magnetic Stimulation (TMS) and Electroencephalography (EEG) are utilized to understand the neurophysiology behind MVF related brain modulations and the temporal processing of MVF in beta waveforms, which may help explain task phase dependent differences in sensorimotor processing, and to examine the effect of incorporating visuomotor goals with the MVF task.

The first goal of this dissertation is to better understand the neurophysiology behind MVF induced modulations in brain activity in healthy populations and how visuomotor tasks combined with mirror feedback can contribute to the final outcome of MVF trainings. A previous functional MRI (fMRI) study has shown primary motor cortex (Ml) and superior parietal regions of the brain to be involved in MVF brain modulation. Recent TMS and fMRI studies from our lab on healthy participants showed greater corticospinal excitability of Ml and ipsilateral parietal activation, respectively when Mirror is combined with target-directed movements. However, these studies do not provide specific information regarding the neurophysiological processes during the training. The interaction of target, or no target involved in the task with visual feedback (mirror, or no mirror) was investigated in a 2x2 factorial design. Electroencephalography (EEG) based measures of event-related synchronization and desynchronization (ERS, ERD) was used to investigate hemispheric activation asymmetry between bilateral motor cortices (C3/4) and superior parietal cortices (CP3/4) in a timing specific manner to dissociate processes related to movement planning and execution. TMS is used to examine corticospinal excitability changes during target-directed MVF and see how combining MVF with targeted tasks can change the excitability in stroke patients' lesioned hemisphere. Ipsilesional Ml excitability was measured using motor evoked potentials before and after each training block. The results reveal evidence that may confirm maximum effect of MVF training when combined with target directed movement. These results may guide future investigations into the application of mirror therapy and brain stimulation protocols to optimize therapy outcomes.

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