Reevaluating Structural and Functional Correlates of Chronic Poststroke Motor Impairment Público

Abstract

Stroke is an increasingly critical public health concern now being the leading cause of long-term adult disability in the United States –the most common disability being upper-extremity movement dysfunction. The interhemispheric imbalance model suggests that abnormal inhibition between hemispheres, specifically greater inhibition of the unaffected primary motor cortex (cM1) on the affected motor cortex (iM1), reduces neuroplasticity and limits maximal recovery of normal arm motor production. This study aimed to investigate the relationship between interhemispheric inhibition (IHI) in stroke with the structural integrity of sensorimotor pathways and with measures of behavioral motor outcomes. 13 individuals with chronic ischemic stroke (mean age: 63.5 ± 11 years, 7 males) completed TMS assessments, diffusion-weighted magnetic resonance imaging scans and behavioral motor assessments. IHI was measured in participants using a TMS paired-pulse paradigm from both cM1 to iM1 and iM1 to cM1. A single-pulse TMS condition (SP120) was performed to determine individual baseline cortical excitability. Both TMS conditions recorded motor-evoked potentials (MEPs) from the contralateral FDI hand muscle of the test-stimulus hemisphere. In contrast to the model, greater IHI was seen from iM1 to cM1 in participants. Measures of lower fiber tract integrity of transcallosal sensorimotor projections was associated with less IHI from cM1 to iM1, trending toward facilitation. Measures of lower fiber tract integrity in the ipsilesional CST were also associated with less IHI in the cM1-to-iM1 condition. Behavioral outcomes assessed using the nine-hole peg test, Wolf motor function test and upper-extremity Fugl-Meyer assessment revealed no relationships with IHI. The results of this study do not support the interhemispheric imbalance model. Rather, the results strengthen recent evidence for the differential roles of cM1 in post-stroke motor recovery based on structural reserve as the degree of inhibition from cM1 to iM1 was associated with structural integrity of sensorimotor pathways. The conflicting literature on the imbalance of IHI after stroke may be related to individual post-stroke outcomes which affect the role of cM1 in upper-limb motor rehabilitation, and should be considered for the future of individualized rehabilitation treatments.

Table of Contents

I.     Background ............................................................................ 1

II.    Methods ................................................................................. 4

a.    Subjects                                                                                       

b.    TMS assessment

c.    EMG recording

d.    Diffusion-weighted magnetic resonance imaging

e.    Upper-extremity motor assessments

f.     Statistical analyses

III. Results ...................................................................................... 10

IV. Discussion ................................................................................. 21

V. Limitations ................................................................................. 24

VI. References ................................................................................. 26

VII. Figures and Tables

a.    Table 1 ............................................................................. 5

b.    Figure 1 ............................................................................ 9

c.    Figure 2 ............................................................................ 11

d.    Figure 3 ............................................................................ 12

e.    Figure 4 ............................................................................ 14

f.     Figure 5 ............................................................................ 15

g.    Figure 6 ............................................................................ 16

h.    Figure 7 ............................................................................ 17

i.     Figure 8 ............................................................................ 18

j.     Figure 9 ............................................................................ 19

k.    Figure 10 .......................................................................... 21

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	Biology, Neuroscience Health Sciences, Rehabilitation and Therapy
Palavra-chave	Motor impairment Transcranial magnetic stimulation Motor function Interhemispheric inhibition Diffusion imaging Stroke
Committee Chair / Thesis Advisor	Borich, Michael, Emory University
Committee Members	Bing, Thomas, Emory University Easterling, Keith, Emory University

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