Brain Inhibition of Muscle Movement in Normal Volunteers
Brain Inhibition of Muscle Movement in Normal Volunteers
This study will use transcranial magnetic stimulation, or TMS (described below), to examine
 how the brain controls muscle movement to prevent unwanted movements in surrounding muscles.
 For example, when a person moves a finger, a part of the brain called the cortex prevents
 unwanted movements in other fingers by a process called cortical inhibition. In people with
 the muscle disorder dystonia, cortical inhibition does not work properly and patients suffer
 from uncontrolled and sometimes painful movements. A better understanding of how this process
 works in normal people may shed light on what goes wrong in dystonia and how the condition
 can be treated.

 Healthy normal volunteers 19 years of age and older may be eligible for this study.
 Candidates will be screened with a medical history and physical and neurological
 examinations. People with a current medical or surgical condition or neurological or
 psychiatric illness may not participate, nor may individuals who are taking medication that
 may influence nervous system function.

 Participants will undergo TMS to record the electrical activity of muscles in the hand and
 arm that are activated by magnetic stimulation. For the procedure, subjects are seated in a
 chair with their hands placed on a pillow in their laps. A wire coil in placed on their
 scalps. A brief electrical current is passed through the coil, creating a magnetic pulse that
 stimulates the brain. Subjects will be asked to move their second finger in response to a
 loud beep or visual cue. In some trials, a brief, mild electrical shock will also be applied
 to the end of either the second or fifth finger. The shock is not painful.

 TMS 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 temporary tingling in the forearm, head, or
 face muscles. The twitching may cause mild discomfort, but the procedure is rarely considered
 painful.
The purpose of this study is to investigate the effect of homotopic and heterotopic sensory
 afferent input on surround inhibition in the motor cortex. Surround inhibition is a cortical
 phenomenon, the function of which may be to suppress unwanted movements in surrounding
 muscles during voluntary actions. In support of this, a recent study showed that motor output
 to the little finger was reduced during self-paced, voluntary movements of the index finger,
 despite an increase in spinal excitability. Work has also shown that in relaxed muscle,
 homotopic and heterotopic peripheral stimulation results in time dependent modulation of
 motor cortical excitability. However, no studies have examined the relationship between
 volitional movement and afferent sensory input on cortical surround inhibition. Therefore,
 the aim of this study is to examine the changes in surround inhibition when electrical
 stimulation is applied to either the finger being actively moved (homotopic stimulation) or a
 separate finger not involved in the movement (heterotopic stimulation) at different time
 periods prior to the initiation of movements to assess the affect of these stimuli on
 surround inhibition and excitation in the motor cortex.
INCLUSION CRITERIA:

 Twenty healthy volunteers older than age 18 will be recruited for the study. Their gender,
 age, or ethnic origin will not provide bias for inclusion to the study. All subjects will
 sign an informed consent prior to participation in the trial.

 EXCLUSION CRITERIA:

 Exclusion criteria for the trial will include any current medical or surgical condition or
 neurological or psychiatric illnesses. Furthermore, any individual who is on medication
 with potential influence on nervous system function, who has a pacemaker, an implanted
 medical pump, a metal plate or metal object in the skull or eye (for example, after brain
 surgery), or who has a history of seizure disorder will be excluded from the trial.