The Physiology of Tricks

Study Summary

This study will examine the action of sensory tricks on an occurrence known as surround inhibition when there is a disorder of muscle tone affecting a single body part in isolation. Surround inhibition refers to a situation that suppresses unwanted movements, known as dystonia, in surrounding muscles during voluntary actions. There are tricks-various actions-that people use to temporarily stop those unwanted movements. Such tricks can include touching the affected body part, placing an object in the mouth, pulling the hair, and others. Often these tricks are beneficial early in the illness but become less effective as it progresses. This study is guided by a hypothesis that sensory tricks will restore surround inhibition and by another hypothesis that it is the application of the tricks, not simply sensory input, that is effective in doing that restoring. Emphasis is on cervical dystonia, involuntary actions affecting the neck, in which the tricks commonly involve the cheeks and chin. The technique used in the study is transcranial magnetic stimulation (TMS). Patients ages 18 and older who have cervical dystonia with at least one effective trick and patients with no effective trick may be eligible for this study. There will also be a control group of healthy participants. Participants will be asked to show the sensory trick and may be asked to be videotaped. During the TMS procedure, they will be seated in a comfortable chair, with hands placed on a pillow on the lap. Small electrodes-soft strips that stick to the skin-will be placed on the skin to record the electrical activity of some muscles in the neck that are activated by the stimulation from TMS. In TMS, there will be a wire coil held over the scalp. A brief electrical current will be passed through the coil, creating a magnetic pulse that stimulates the brain. Patients will hear a click and may feel a pulling sensation on the skin under the coil. There may be muscle twitches of the face, arm, or leg. In ad