Citation

Thirugnanasambandam N, Khera R, Wang H, Kukke SN, Hallett M. J. Neurophysiol. 2015; 114(2): 1102-1108.

Affiliation

National Institutes of Health hallettm@ninds.nih.gov.

Copyright

(Copyright © 2015, American Physiological Society)

DOI

10.1152/jn.00791.2014

PMID

26041828

Abstract

Surround inhibition (SI) is a feature of motor control in which activation of task-related muscles is associated with inhibition of neighboring, non-protagonist muscles, allowing selective motor control. The physiological basis for SI still remains unknown. In all previous studies, SI in the motor system was measured during movement initiation using transcranial magnetic stimulation (TMS) to deliver a postero-anterior current at single supra-threshold intensity. To expand our understanding of SI, we explored this phenomenon at a wide range of intensities and by stimulating motor cortex with currents along antero-posterior and latero-medial directions. Fifteen healthy volunteers performed a brief isometric index finger flexion on hearing a tone. Electromyography was recorded from the synergist and surround finger muscles. Single-pulse TMS was applied to stimulate the surround muscle at different intensities at rest or movement initiation. The motor evoked potential (MEP) amplitudes were then plotted against stimulation intensities to obtain the MEP recruitment curves for the rest and movement initiation conditions, and for the three current directions for every subject. From the recruitment curves, we found that surround inhibition could be elicited only by the postero-anterior current. Hence we postulate that surround inhibition is mediated by intracortical circuits in the motor cortex. Also, for the first time we observed surround facilitation when the motor cortex was stimulated with antero-posterior current. Further studies are needed to investigate the mechanisms underlying both these phenomena individually in healthy subjects and patients with dystonia and other movement disorders.

Language: en