Interaction of Right and Left Brain Hemispheres in Learning Precision Hand Movements
Condition: Interhemispheric Inhibition
Study type: Observational

Summary: 
      This study will examine how the two sides of the brain interact when learning precision hand
      movements. Both sides of the brain are active when a person performs an accurate hand
      movement. This study will look at the extent to which the two brain hemispheres interact when
      learning accurate hand movements.

      Healthy, right-handed normal volunteers 18 - 40 years of age may be eligible for this study.
      Candidates are screened with a clinical and neurological examination.

      Participants are randomly assigned to one of two groups - precision or non-precision hand
      movements. All participants undergo the following procedures:

        -  Force precision task: Subjects are press a small device between the thumb and index
           finger. The force produced with the fingertips is translated onto a computer screen.
           Subjects track a white line passing on the screen with their fingertips.

        -  Paired-pulse transcranial magnetic stimulation (TMS): A wire coil is held to the
           subject's scalp. A brief electrical current is passed through the coil, creating a
           magnetic pulse that stimulates the brain. During the stimulation, the subject may be
           asked to tense certain muscles slightly or perform other simple actions. The stimulation
           may cause a twitch in muscles of the face, arm, or leg, and the subject may hear a click
           and feel a pulling sensation on the skin under the coil. The effect of paired-pulse TMS
           on the muscles is detected with electrodes taped to the skin on the arms or legs.

        -  Surface electromyography (EMG): This test measures the electrical activity of muscles.
           For this test, electrodes are filled with a gel and taped to the skin over the muscle to
           be tested.

      The study involves six sessions. Sessions 1-5 are on consecutive days; session 6 is one week
      after session 5.

        -  Session 1: Familiarization with the motor task and baseline measurements, including
           error rate, EMG, and paired-pulse TMS

        -  Session 2: Training in the motor task and repeat measurements as in session 1

        -  Session 3: Training and measurements as in session 2

        -  Session 4: Training and measurements as in session 2

        -  Session 5: Training and measurements as in session 2

        -  Session 6: Measurements only
    

Detailed description: 
      The purpose of this protocol is to investigate the changes in interhemispheric inhibition
      (IHI) between human motor cortices with learning of performance of an accurate motor task
      (pinch force control). Performing a simple motor task is associated with activation in the
      contralateral motor areas. Activation of the ipsilateral motor/premotor cortex might be
      elicited by performing more challenging and difficult unimanual motor tasks. However, the
      functional role played by this ipsilateral activation has been controversial, and is felt to
      be more prominent with more complex tasks. Several studies using paired-pulse transcranial
      magnetic stimulation (TMS) revealed a significant IHI from the active upon the non-active
      hemisphere. Together these results suggested IHI between motor cortical areas may play a
      critical role in motor control and could influence manual dexterity. Taking these into
      account, it raises the interesting question of whether the IHI balance between both motor
      cortices is progressively modified during the learning phase of an accurate motor task. We
      hypothesize that learning to perform a tracking motor task requiring accurate control of
      pinch force generation (Tracking accurate), will increase IHI from the "learning" to the
      "non-learning" hemisphere to a larger extent than learning to perform a less precise tracking
      motor task (Tracking non-accurate). The primary outcome measure will be the amount of changes
      in IHI from the "learning" to the "non-learning" hemisphere as a function of learning both
      motor tasks.
    

Keywords: Transcranial Magnetic Stimulation (TMS); Motor Learning; Accuracy; Tracking Motor Task; Healthy Volunteer; HV