Enhancing Brain Activity With Magnetic Stimulation
Condition: Healthy
Study type: Observational

Summary: 
      This study will determine whether stimulation of the right side of the brain with repetitive
      transcranial magnetic stimulation (rTMS) followed by stimulation of the left side with theta
      burst stimulation (TBS) can temporarily change brain activity and improve hand movements in
      subjects more than has recently been achieved with rTMS alone.

      For rTMS, a wire coil is held on the patient's scalp. A brief electrical current is passed
      through the coil, creating a magnetic pulse that stimulates the brain. The subject hears a
      click and may feel a pulling sensation on the skin under the coil. There may be a twitch in
      the muscles of the face, arm or leg. The subject may be asked to tense certain muscles
      slightly or perform other simple actions. The effect of TMS on the muscles is detected with
      small metal disk electrodes taped to the skin of the arms or legs. This study uses two kinds
      of rTMS. In one (Hz rTMS), magnetic pulses are given once per second for a period of 20
      minutes; in the other (TBS), a series of pulses are given in bursts, each lasting 2 seconds,
      for a period of 3 minutes.

      Healthy normal volunteers between 18 and 55 years of age may be eligible for this study.
      Participants undergo the following procedures during three visits to the NIH Clinical Center:

      Visit 1:

      Participants receive either real or sham rTMS applied on the right side of the brain followed
      by real or sham TBS applied on the left side of the brain. In addition, subjects undergo the
      following:

      " Pinch force: Subjects press a wedged instrument between the thumb and index finger as hard
      as they can during several trials every 10 seconds.

      " Speed tapping: Subjects press a key on a computer keyboard as quickly as possible for 10
      seconds, repeated for several trials.

      " Simple reaction time: Subjects respond as quickly as possible to a "go" signal presented on
      a computer monitor by performing a quick wrist movement.

      " Electromyography: Subjects' muscle activity is recorded using electrodes (small metal
      disks) filled with conductive gel and taped to the skin over the muscle.

      Visits 2 and 3

      Visit 2 is scheduled for one day after visit 1, and visit 3 is one week after visit 1.
      Participants do not have brain stimulation during these two visits, but they have TMS
      measurements, behavioral measurements, and electromyography (EMG) to see if the brain
      stimulation done during the first visit is still present after a period of time.

      At all three visits, participants comp...
    

Detailed description: 
      OBJECTIVES:

      Previous studies have demonstrated that single-pulse transcranial magnetic stimulation (TMS)
      applied to the primary motor cortex (MI) exerts a transient inhibitory effect on the
      contralateral MI. Furthermore, down-regulation of excitability in MI of one hemisphere by 1Hz
      rTMS results in increased excitability in the homologous MI accompanied by performance
      improvements in simple motor tasks performed by the hand ipsilateral to rTMS. It has been
      proposed that this phenomenon relies on interhemispheric disinhibition between both MI.
      Furthermore, interhemispheric disinhibition is also a promising method for boosting
      neurorehabilitation since interhemispheric disinhibition has been successfully applied in
      stroke patients to enhance motor cortex excitability and hand function or reduce aphasia. The
      purpose of this protocol is to test the hypothesis that interhemispheric disinhibition of the
      left MI by down-regulating activity in the right MI can be further enhanced by additional
      up-regulation targeting the left MI.

      STUDY POPULATION:

      We will study a total number of 72 healthy volunteers between the ages of 18-55.

      DESIGN:

      To test the hypothesis, subjects will be randomly allocated to one of 4 experimental sessions
      (parallel design). Subjects will receive different types of combined brain stimulation (1 Hz
      rTMS and Theta Burst Stimulation [TBS]) to the right and left MI. The primary outcome measure
      will be the amount of changes in cortical excitability, as reflected by recruitment curves
      (RC) of motor evoked potentials (MEPs) elicited by single-pulse TMS over the left MI.
      Additionally, we will test changes in short-interval intracortical inhibition (SICI) and
      facilitation (ICF) as well as the modulation of interhemispheric inhibition (IHI) between
      both MI. The secondary outcome measures will include simple motor tasks such as finger
      tapping, pinch force/acceleration and reaction time of the right hand.

      In summary, we believe that this approach might identify additional effective strategies to
      enhance functional recovery after stroke and might provide deeper insight into the neural
      substrates involved in performance improvements after bilateral brain stimulation.
    

Keywords: Theta Burst Stimulation; Repetitive TMS (rTMS); Transcranial Magnetic Stimulation (TMS); Primary Motor Cortex; Interhemispheric Disinhibition; Healthy Volunteer; HV