OBJECTIVE: To investigate whether hand muscle repetitive use reduces surround inhibition (SI) as observed in patients with focal hand dystonia, we performed a transcranial magnetic stimulation (TMS) study in 15 healthy right-handed volunteers.
METHODS: TMS was set to be triggered by self-initiated flexion of the index finger at 3ms after movement onset. Motor evoked potentials (MEPs) of the abductor digiti minimi (ADM) were measured before and at 0, 10, 20 and 30min after 'single' (little finger abduction) and 'dual' (both index finger flexion and little finger abduction) exercise at 0.5Hz for 30min. SI was calculated as (mean control MEP - mean self-triggered MEP)×100/mean control MEP.
RESULTS: Compared to single exercise, dual exercise produced significantly larger and longer-lasting enhancements of self-triggered MEPs, and greater reduction in calculated SIs.
CONCLUSIONS: This result demonstrates that synchronized finger exercise can reduce SI between the involved muscles possibly due either to the strengthening of the excitatory connections or to the weakening of the inhibitory connections between them, and may illustrate the association between hand muscle repetitive use and disturbed SI observed in FHD.
SIGNIFICANCE: The operation of surround inhibition can be reduced by practicing synchronous movements.