Propensity to Develop Plasticity in the Parieto-Motor Networks in Dystonia From the Perspective of Abnormal High-Order Motor Processing

Background: \- People with dystonia have muscle contractions they can t control. These cause slow, repeated motions or abnormal postures. People with dystonia have abnormalities in certain parts of the brain. Researchers want to study the activity of two different brain areas in people with writer s cramp and cervical dystonia. Objective: \- To compare brain activity in people with dystonia to that in healthy people. Eligibility: * Right-handed people ages of 18-65 with cervical dystonia or writer s cramp. * Healthy volunteers the same ages. Design: * Participants will be screened with a physical exam. They will answer questions about being right- or left-handed. * At study visit 1, participants will:\<TAB\> * Have a neurological exam. * Answer questions about how their disease impacts their daily activities. * Have a structural magnetic resonance imaging (MRI) scan. Participants will lie on a table that can slide \<TAB\>in and out of a metal cylinder. This is surrounded by a strong magnetic field. * Do 2 simple computer tasks. * At study visit 2: * Participants will have transcranial magnetic stimulations (TMS) at 2 places on the head. Two wire coils will be held on the scalp. A brief electrical current creates a magnetic pulse that affects brain activity. Muscles of the face, arm, or leg might twitch. Participants may have to tense certain muscles or do simple tasks during TMS. They may be asked to rate any discomfort caused by TMS. * Muscle activity in the right hand will be recorded by electrodes stuck to the skin of that hand.

Objective: The purpose of this protocol is to improve understanding of the pathophysiology of dystonia by performing an electrophysiological study using plasticity induction protocols based on dual-site transcranial magnetic stimulation (TMS). We hypothesize that dystonic patients have enhanced responsiveness to plasticity induction in the parieto-motor network. The clinical significance of such an enhanced plasticity will be evaluated by correlating the plasticity measurements with subjects' performance on two tasks engaging high-order motor processing and involving the parietal cortex. Study population This study will explore the parieto-motor network (PAR study). There will be two independent arms in each study: one will compare patients with writer s cramp (WC) and age-matched healthy volunteers (HV); and the other one will compare patients with cervical dystonia (CD) with age-matched HVs. The power analysis of thePAR study indicates that we need to enroll 17 patients and 17 healthy volunteers in each arm, with an additional 3 added to account for drop-outs. Therefore, we request a maximum of 20 subjects per patient group and 40 subjects for the control groups. Design Subjects will come for one screening visit and two outpatient study visits. During the first study visit patients will be scored clinically for dystonia. They will also undergo a structural magnetic resonance imaging (MRI) to locate the parietal target during the stimulation session. At least 24 hours later, during study visit two, subjects will receive TMS. TMS-induced electromyographic (EMG) activity of hand muscles will be recorded as motor evoked potentials (MEPs). Using single TMS shocks, we will measure at baseline, the input-output (I-O) curve for the right first dorsal interosseous (FDI) muscle MEPs. Then, the subjects will receive a plasticity induction protocol aiming to induce plasticity in the pathway linking the posterior parietal (PP) cortex and the primary motor cortex (M1). To that end, transcranial stimulation will be applied repeatedly (100 pairs) to the left angular gyrus in the PP cortex and to the left M1. At the end of the intervention, the I-O curve will be measured again over the next 50 minutes. Outcome measures The amplitude of the MEPs in the I-O curves gives information about corticospinal excitability as a function of TMS stimulation. The primary outcome measure will be the relative change of the MEP size with respect to time (before and 15-20 min after the plasticity intervention). The difference in MEP size will be compared between the HV and the patient groups using a T test.