Neuromodulation of Interhemispheric Connectivity by Paired Associative Stimulation after Stroke Open Access

Abstract

Atypical interhemispheric connectivity has been observed in stroke survivors. Specifically, the presence of excessive interhemispheric inhibition (IHI) from the contralesional motor cortex (cM1) to ipsilesional motor cortex (iM1) (cM1-to-iM1 IHI) created a model of interhemispheric competition after stroke which may contribute to motor recovery. Paired associative stimulation (PAS) was found to be able to induce spike-timing-dependent plasticity, which is essential for motor relearning during rehabilitation. However, it is unknown how modulation of IHI through transcranial magnetic stimulation (TMS) might influence post-stroke motor function. The purpose of this study was to 1) determine the effect of a session of interhemispheric paired associative stimulation (ihPAS) on neuromodulation of cortical excitability, IHI, and motor performance in stroke survivors and 2) investigate the relationship between IHI and post-stroke motor function.

Thirteen participants (7 male) with ischemic chronic (>6 mo.) stroke were tested during two separate sessions with two ihPAS conditions: ihPAS8ms (interstimulus interval [ISI] of 8ms) and ihPAS1ms (ISI of 1ms). ihPAS consisted of 100 paired TMS pulses to cM1 followed by iM1 delivered at 0.25Hz. Electromyography (EMG) were placed on first dorsal interosseous muscles to measure the motor evoked potential upon TMS stimulations. IHI and cortical excitability were assessed by TMS before and after ihPAS. Motor function and skill learning were assessed by both 3-item Wolf Motor Function Test and serial reaction time task. ihPAS did not significantly modulate iM1 cortical excitability and cM1-to-iM1 IHI, but paretic motor function was improved following ihPAS8ms. cM1-to-iM1 IHI was not strongly correlated with paretic arm motor function. Contrary our hypothesis, there was greater iM1-to-cM1 IHI than cM1-to-iM1 IHI prior to ihPAS. Secondary analyses revealed that those demonstrating exaggerated cM1-to-iM1 IHI before ihPAS had decreased cM1-to-iM1 IHI compared to those who showed diminished IHI. Our results suggest that the effect of ihPAS is variable across individuals. The absence of exaggerated cM1-to-iM1 IHI does not support the interhemispheric competition model. Future studies are necessary to further characterize the role of cM1-to-iM1 IHI in the motor recovery process on an individual level to develop effective therapies.

Table of Contents

Introduction.………………………………………………………………..1

Methods.……………………………………………………………………..6

Results ……………………………………………………………………….13

Discussion…………………………………………………………………..26

References………………………………………………………………….33

About this Honors Thesis

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School	Emory College
Department	Neuroscience and Behavioral Biology
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Health Sciences, Rehabilitation and Therapy
Keyword	Stroke Transcranial magnetic stimulation Neurorehabilitation
Committee Chair / Thesis Advisor	Borich, Michael , Emory University
Committee Members	Fisher, David, Emory University Lennard, Paul, Emory University

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