The contribution of the contralesional motor cortex to the impaired limbs is still controversial. The aim of this study was to investigate the role of descending projections from the contralesional hemisphere during voluntary elbow flexion on the paretic side.
Eleven healthy and 10 stroke subjects performed unilateral isometric elbow flexion tasks at various submaximal levels. Transcranial magnetic stimulation was delivered to the hotspot 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 amplitudes of the contralateral resting biceps muscles, transcranial magnetic stimulation–induced ipsilateral force increment, and reflex torque and weakness of spastic elbow flexors were quantified.
The normalized motor-evoked potential 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.
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.
From the Department of Physical Medicine and Rehabilitation, McGovern Medical School University of Texas Health Science Center – Houston, Houston, Texas (Y-TC, Shengai Li, PZ, Sheng Li); TIRR Research Center, TIRR Memorial Hermann Hospital, Houston, Texas (Y-TC, Shengai Li, PZ, Sheng Li); and Department of Physical Medicine and Rehabilitation, Baylor College of Medicine, Houston, Texas (CDT).
All correspondence should be addressed to: Sheng Li, MD, PhD, 1333 Moursund, Houston, TX 77030.
This study was supported in part by National Institute of Health Eunice Kennedy Shriver National Institute of Child Health and Human Development/National Center for Medical Rehabilitation Research R21HD087128 and R21HD090453.
The study was selected for the Best Paper Award in the Fellow Category and was presented at Association of Academic Physiatrists 2018 Annual Meeting, February 15, 2018, Atlanta, GA.
Yen-Ting Chen is in training.
Financial disclosure statements have been obtained, and no conflicts of interest have been reported by the authors or by any individuals in control of the content of this article.
Online date: January 23, 2019