Proceedings of The Physiological Society

University College London December 2005 (2006) Proc Physiol Soc 1, PC4

Poster Communications

Transcallosal sensorimotor integration  effects of sensory input on cortical projections to the contralateral hand

Swayne, Orlando; Rothwell, John C; Rosenkranz, Karin;

1. Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, London, United Kingdom.

Low amplitude vibration of forearm or hand muscles predominantly activates proprioceptive inputs that influence corticospinal projections in a focal manner, increasing output to the stimulated muscle while reducing output to neighbouring muscles [1]. Modulation of contralateral forearm muscles by vibration has also been reported on one occasion [2]. The aim of the current investigation was to investigate the effects of proprioceptive input from a hand muscle on corticospinal excitability, intracortical inhibition (SICI) and interhemispheric inhibition (IHI) targeting the homologous contralateral muscle. Transcranial magnetic stimulation (TMS) was delivered to the left cortical hand area of ten healthy subjects and surface electromyography (EMG) recordings taken from the right first dorsal interosseus (FDI) and abductor digiti minimi (ADM). The effect of low amplitude vibration of the left FDI on MEP amplitudes, SICI and IHI targeting the right hand was assessed. Vibration of the left FDI caused a significant reduction in MEP amplitudes in the homologous right FDI but not in ADM. SICI and IHI targeting the right FDI were also significantly increased but were unchanged in ADM. These increases in inhibition occurred despite controlling for the amplitude of baseline MEPs. We conclude that proprioceptive input from a hand muscle reduces the corticospinal excitability of the contralateral homologous muscle. Although vibratory input is known to affect the excitability of spinal alpha motor neurons [3], the increase in SICI suggests that at least some of this effect occurs in the cortex ipsilateral to the stimulus. The observed increase in IHI suggests that such changes may be mediated via transcallosal fibres. These results suggest that sensory input can modulate excitability in both motor cortices simultaneously, as well as the relationship between them. Interventions which modulate this transcallosal relationship may become useful in disorders where abnormal IHI is a potential therapeutic target [4].

Where applicable, experiments conform with Society ethical requirements