Interhemispheric Plasticity in Humans
Condition: Healthy
Study type: Observational

Summary: 
      This study will determine how the brain controls movements by sending messages to the spinal
      cord and muscles. Researchers want to know if strengthening a hand muscle will increase the
      strength of the same muscle in the other hand, and if these changes happen in the brain or
      spine, or both. Plasticity in this study refers to the capacity for continuous changes of the
      neural pathways in the brain and nervous system. Researchers have seen cases in which using a
      muscle extensively (force production) in one muscle group has increased the strength of the
      same muscle group on the opposite side of the body (force transfer). This situation happens
      without the unused muscle becoming larger-suggesting that the practice causes changes in some
      parts of the brain or spine. It is vital for scientists to know how this effect works, so
      that they can create new rehabilitation methods for people who cannot move or who have
      difficulty moving one side of their body.

      Patients ages 18 to 60 who are in good health and who do not have a history of major
      conditions affecting the bones, joints or nervous system may be eligible for this study.
      Patients will undergo a medical examination. There will be 1 or 2 testing sessions, 20
      training sessions, and 1 or 2 final testing sessions, with patients being asked to come to
      the laboratory for as few as 4 times (about 10 hours total) or for up to 25 visits (about 20
      hours total). The investigator will indicate which of six different groups that a patient is
      selected for.

      During testing sessions, the strength of the pointer and little fingers in each hand will be
      determined through the use of very brief electrical pulses. There also will be transcranial
      magnetic stimulation (TMS) and 1 Hz TMS. The researchers will place one or two wire coils on
      the patient's scalp and make marks on the scalp which will be removed at the end of the
      session. During the TMS, a brief electrical current is passed through the coil, creating a
      magnetic pulse that stimulates the brain. Patients will hear a click sound and feel a
      snapping sensation on the skin. They may also feel and see small twitches in the hand
      muscles, and the fingers or wrist may move. There will be a total of about 300 magnetic
      stimuli, at a rate of 10 pulses per minute. Patients will also have an electromyogram (EMG),
      a procedure recording electrical activity in the muscles that are activated by electrical or
      magnetic stimulation. Metal electrodes will be attached to the skin over the muscle. During
      the EMG, patients will be asked to tense certain muscles slightly. Depending on the group a
      patient is assigned to, he or she may be asked to use the right index finger by using
      voluntary muscle movement, electrical stimulation, his or her imagination, electrical
      stimulation of a different hand muscle, or voluntary movements immediately followed by
      repetitive TMS.

      Regardless of group assignment, there will be five blocks of 10 repetitions of finger
      exercise per session, 200 per week, and 1,000 throughout the whole study. During the study
      sessions, patients will be able to talk and move around. They can take a break and leave the
      room if needed. In most cases, the session will take less than 2 hours. There also will be a
      control group whose members will not be training their fingers but who will participate only
      in the testing sessions. TMS is a safe procedure; however, strong contractions of scalp
      muscles have been known to cause headaches. Also, because of the distracting noise of the
      TMS, patients will be fitted with earplugs to wear during the procedure.

      Compensation for research-related discomfort and inconvenience will be made to participants,
      with a maximum of $500 to $600, depending on assignment to groups. This study will not have a
      direct benefit for participants. However, researchers hope to gain information that will help
      them better understand how the two sides of the brain control movement and how they affect
      each other regarding movement control.
    

Detailed description: 
      Strength training of a limb muscle on one side of the body produces functionally and
      clinically meaningful increases in motor output of the same muscle on the opposite side of
      the body. Such adaptations occur without muscle hypertrophy, implying a role for the
      ipsilateral motor cortex and the spinal cord in force transfer. The goal of this project is
      to determine the interhemispheric and spinal mechanisms of force transfer in healthy young
      adults. We hypothesize that the effects of unilateral practice on interhemispheric inhibition
      (IHI) and on the excitability of the contralateral corticospinal projections are linked, and
      these effects are graded according to the nature of muscle activation. In a series of
      experiments on healthy adults age 18 to 60, we will characterize the motor cortical
      inhibitory and excitatory mechanisms of interhemispheric practice-induced transfer of muscle
      force.

      We will use a longitudinal design that will include three exercise groups. In 20 sessions
      over 4 weeks, subjects will strengthen their first dorsal interosseus (FDI) muscle of the
      dominant hand either with voluntary, electrically stimulated, or imagined contractions. The
      design also includes three control groups, a sham-stimulated group, a repetitive transcranial
      magnetic stimulation (1HzTMS) group, and a no-intervention group. Before and after the
      training programs, we will determine the changes in the outcome measures, including voluntary
      and electrical stimulation evoked force of the trained and the untrained FDI. Measures of
      excitability of the involved and uninvolved motor cortex, assessed with TMS, and measures of
      spinal cord excitability, assessed with peripheral nerve stimulation, are the additional
      outcome measures. The results of these studies will substantially increase our understanding
      of central nervous system (CNS) control of voluntary movement in health and disease.
    

Keywords: Exercise; Stimulation; Nerve; Electrical; Muscle; Healthy Volunteer; HV