Effects of tDCS Over the Cerebellum on Motor Function
Condition: Healthy
Study type: Observational

Summary: 
      This study will evaluate whether applying electrical stimulation on the cerebellum (posterior
      and lower part of the brain) can influence brain excitability and hand movement performance.

      A new technique became available to stimulate the brain: transcranial direct current
      stimulation (tDCS), which could improve the ability to learn. Researchers do not know whether
      applying tDCS over the cerebellum could also influence motor function, and they want to
      examine changes in brain excitability, by using transcranial magnetic stimulation (TMS).

      Patients ages 18 to 40 who are not pregnant may be eligible for this study. They will come to
      NIH for a medical history and completing a questionnaire about memory and attention. There
      will be five experiments, each up to 5 hours, for about 1 to 5 weeks, in which patients
      perform tasks like pinching a special device between the thumb and index fingers, or reaching
      for target objects on the computer screen. Patients will receive mild electrical stimulation
      over a different part of the head each day. Some experiments are done without the electrical
      current, but patients will not know which ones are with or without stimulation. There are
      also short questionnaires about attention, fatigue, and mood, to be completed before, during,
      and after each experiment.

      Patients will be connected to an electromyography (EMG) machine, to measure electrical
      activity of muscles. Electrodes are taped to the skin over one small hand muscle. TMS allows
      electrical pulses to pass through the brain to stimulate it. TMS is used at the beginning of
      each experiment to determine the precise location on the scalp of two target areas:
      cerebellum and motor cortex. TMS is a safe procedure. Discomfort, headache, or nausea can
      occur, but all symptoms usually go away promptly. During motor learning under tDCS, also a
      safe procedure, patients sit in a comfortable chair, and the arm and wrist and arm are kept
      still. Sponge electrodes are applied on the chin, back of the head, neck, collarbone, lateral
      part of the head, or above the eyebrow. A small electrical current is passed between
      electrodes. Patients may feel an itching or tingling sensation under the electrodes or see
      slight light flashes. tDCS is applied for 20 to 30 minutes. A magnetic resonance imaging
      (MRI) scan, which may also be involved, uses a strong magnetic field and radio waves to
      obtain images of body organs and tissues. Patients lie on a table in a cylinder and may be
      asked to lie still for up to 60 minutes at a time.

      This study will not have a direct benefit for participants. However, knowledge gained may
      help researchers identify ways to improve movement in people with a brain injury, such as
      chronic stroke.
    

Detailed description: 
      Objectives

      Non-invasive brain stimulation can modulate motor function in healthy volunteers and stroke
      patients when applied over the primary motor cortex (M1). M1 is an evident target for
      therapeutic interventions given its key role in motor control and learning. However, given
      the wide variety of motor dysfunctions following focal neurological injuries such as stroke,
      it is desirable to find out whether alternative neuronal structures could also be responsive
      to non-invasive brain stimulation for enhancing motor recovery. The cerebellum is an
      attractive target for therapeutic non-invasive brain stimulation since (i) the cerebellum
      plays a pivotal role in motor learning of reaching and movement synchronization tasks, (ii)
      the deep cerebellar nuclei are involved in the regulation of M1 neuronal activity through
      their excitatory drive to M1, and (iii) the cerebellum may be adaptively recruited after
      brain injury.

      The purpose of this study is to find out if application of non-invasive transcranial DC
      stimulation (tDCS) can modulate motor cortical function. We hypothesize that tDCS of the
      cerebellar hemisphere ipsilateral (Cerebellum IPSI) to the target hand will modulate
      corticomotor excitability and motor function in healthy volunteers.

      Study Population

      40 healthy volunteers (18-40 years).

      Design

      This proof of principle study will determine if tDCS applied over the cerebellum can modulate
      focally motor excitability (as assessed by TMS) and motor performance. The stimulation
      parameters to be studied are polarity (anodal, cathodal and sham tDCS) and intensity (1 mA
      and 2 mA). The focality of stimulation will be addressed by applying tDCS over the neck and
      over M1 in separate control sessions, and by monitoring changes in cerebello-cortical
      excitability with paired-pulse TMS.

      The outcome measures will be changes in motor cortical excitability as measured with TMS and
      in performance of an isometric pinch force task, a reaching task, and a motor sequence timing
      task. Attention and mood will be assessed to rule out nonspecific arousal effects.
      Paired-pulse TMS will be used to demonstrate modulations in cerebello-cortical connections
      and to characterize changes in intra-cortical excitability.
    

Keywords: Transcranial Direct Current Stimulation (tDCS); Plasticity; Primary Motor Cortex; Cerebellum; Transcranial Magnetic Stimulation (TMS); Healthy Volunteer; HV