The purpose of this study is to investigate the mechanism of sensory tricks on surround inhibition in the motor cortex in focal dystonia. Sensory tricks or Geste antagoniste, are various manoeuvres used by dystonic patients to transiently diminish their spasms. Many of these manoeuvres involve motor as well as sensory input and here we use the term 'tricks' to refer to both phenomena. Little is known of this unique feature that is an evidence for the abnormality of sensorimotor integration in focal dystonia. The relief of dystonic symptoms by the application of tricks suggests its potential as a clue to the understanding of the yet unclear mechanism of dystonia. There is evidence that surround inhibition, a cortical phenomenon that functions to suppress unwanted movements in surrounding muscles during voluntary actions, is impaired in dystonia. Since tricks transiently relieve the dystonic symptoms, we hypothesize that the mechanism of tricks is the normalization of surround inhibition which is defective in dystonia.
INCLUSION CRITERIA: Nineteen patients age 18 or over with cervical dystonia with a minimal of one effective trick, 15 patients age 18 and over with cervical dystonia with no effective trick will be recruited for the study. For patients, the selection criteria are the presence of cervical dystonia and the minimal of one sensory trick in the patient with trick group, and no trick in the patient without trick group. The interview of dystonic patients will be focused on medical history, neurologic examination and effectiveness of the patient's tricks which will be accessed by measuring the degree of head rotation before and during trick application. The diagnosis of dystonia will rely on review of medical record, history, and clinical evaluation. For the patients that are receiving botulinum toxin injections, the evaluation will be done 3 months after their last injection. Their gender, age, or ethnic origin will not provide bias for inclusion to the study. There is no evidence of higher prevalence of dystonia in any particular race, thus the races and ethnicity of the subjects recruited for this study will approximate that of the general population. Fifteen normal subjects age 18 and over will be recruited for the control group. The controls will not have dystonia or any other neurological condition. All subjects will sign an informed consent prior to participation in the trial, and the trial will be approved by the NINDS IRB committee. EXCLUSION CRITERIA: Exclusion criteria for the trial covering both the normal control and dystonia group will include; 1. Any concurrent medical or surgical condition as well as neurological or psychiatric illnesses. 2. Any individual who is on medications with potential influence of the nervous system function (antidepressants, antianxiolytics, anticonvulsants, antipsychotic, antiparkinsonian, hypnotics, and stimulants). 3. Patients who have received Botulinum toxin injections within 3 months of starting the protocol. 4. Individual who has a pacemaker, an implanted medical pump, a metal plate or medical object in the skull or eye (for example, after brain surgery) 5. Individual with a history of seizures.