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
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.
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 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.