Possible contributions of ipsilateral pathways from the contralesional motor cortex to the voluntary contraction of the spastic elbow flexors in stroke survivors: a TMS study

Objective The contribution of the contralesional motor cortex to the impaired limbs is still controversial. The purpose of this study was to investigate the role of descending projections from the contralesional hemisphere during voluntary elbow flexion on the paretic side. Design Eleven healthy and 10 stroke subjects performed unilateral isometric elbow flexion tasks at various submaximal levels. Transcranial magnetic stimulation (TMS) was delivered to the hot spot of biceps muscles ipsilateral to the target side (paretic side in stroke subjects or right side in controls) at rest and during elbow flexion tasks. Motor evoked potential (MEP) amplitudes of the contralateral resting biceps muscles, TMS-induced ipsilateral force increment, and reflex torque and weakness of spastic elbow flexors were quantified. Results The normalized MEP amplitude increased with force level in both healthy and stroke subjects. However, stroke subjects exhibited significantly higher force increment compared with healthy subjects only at low level of elbow flexion, but similar at moderate to high levels. The greater force increment significantly correlated with reflex torque of the spastic elbow flexors, but not weakness. Conclusion These results provide novel evidence that ipsilateral projections are not likely to contribute to strength, but are correlated to spasticity of spastic-paretic elbow flexors after stroke. Correspondence: Sheng Li, MD, PhD, 1333 Moursund, Houston, TX 77030, Tel: 713-797-7125, E-mail: sheng.li@uth.tmc.edu Author Disclosures: Include an explanation of the following. Competing Interests: None. Funding or grants or equipment provided for the project from any source: This study was supported in part by NIH NICHD/NCMRR R21HD087128, R21HD090453. Financial benefits to the authors: None Details of any previous presentation of the research, manuscript, or abstract in any form: The study was selected for the Best Paper Award in the Fellow category, and was present at AAP 2018 annual meeting in Atlanta, GA on 2/15/2018. Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.

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