Short-latency afferent inhibition during selective finger movement.

During individual finger movement, two opposite phenomena occur at the level of the central nervous system that could affect other intrinsic hand muscle representations, unintentional co-activation, and surround inhibition (SI). At rest, excitability in the motor cortex (M1) is inhibited at about 20 ms after electric stimulation of a peripheral nerve [short-latency afferent inhibition (SAI)]. We sought to determine whether SAI changes during selective index finger movement. Effects were measured by the response to transcranial magnetic stimulation in two functionally distinct target muscles of the hand [abductor digiti minimi muscle (ADM), first dorsal interosseus muscle (FDI)]. An increase in SAI in the ADM during index finger movement compared to at rest could help explain the genesis of SI. Electrical stimulation was applied to either the little finger (homotopic for ADM, heterotopic for FDI) or the index finger (heterotopic for ADM, homotopic for FDI). During index finger movement, homotopic SAI was present only in the ADM, and the effect of peripheral stimulation was greater when there was less co-activation. Heterotopic SAI found at rest disappeared with movement. We conclude that during movement, homotopic SAI on the muscle in the surround of the intended movement may contribute to SI.