Surround Inhibition in Patients With Dystonia

Overview

This study will use transcranial magnetic stimulation (TMS) to examine how the brain controls muscle movement in dystonia. Dystonia is a movement disorder in which involuntary muscle contractions cause uncontrolled twisting and repetitive movement or abnormal postures. Dystonia may be focal, involving just one region of the body, such as the hand, neck or face. Focal dystonia usually begins in adulthood. Generalized dystonia, on the other hand, generally begins in childhood or adolescence. Symptoms begin in one area and then become more widespread. Healthy normal volunteers and patients with focal \[or generalized\] dystonia \[between 21 and 65 years of age\] may be eligible for this study. Participants will have transcranial magnetic stimulation. For this test, subjects are seated in a comfortable chair, with their hands placed on a pillow on their lap. An insulated wire coil is placed on the scalp. A brief electrical current is passed through the coil, creating a magnetic pulse that stimulates the brain. (This may cause muscle, hand or arm twitching if the coil is near the part of the brain that controls movement, or it may induce twitches or transient tingling in the forearm, head or face muscles.) During the stimulation, subjects will be asked to either keep their hand relaxed or move a certain part of the hand in response to a loud beep or visual cue. Metal electrodes will be taped to the skin over the muscle for computer recording of the electrical activity of the hand and arm muscles activated by the stimulation. There are three parts to the study, each lasting 2-3 hours and each performed on a separate day.

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.