Surround Inhibition in Patients With Dystonia

The purpose of this study is to evaluate modulation of inhibition within the motor cortex before and during movement in patients with focal dystonia. For a selective movement or task, certain muscles are normally recruited and others are inhibited at the cortical level. We hypothesize that a disturbance in this cortical inhibitory control could result in a failure to focus the desired motor action within the motor cortex (disturbed center surround inhibition) and may account for co-contraction of antagonist muscles and overflow into extraneous muscles in dystonic patients. Intracortical inhibition (ICI) and silent period (SP) are two major cortical inhibitory mechanisms demonstrated by transcranial magnetic stimulation (TMS). Alteration in these inhibitory mechanisms have been studied in dystonia at rest, however, as dystonic symptoms mainly occur with selective tasks or movements we plan to study intracortical inhibitory mechanisms before and during movement using different TMS paradigms.