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.
- INCLUSION CRITERIA: - age between 18-40 years - able to perform tasks required by the study - willing and able to give consent EXCLUSION CRITERIA: - unable to perform the tasks required by the study - history of severe alcohol or drug abuse, psychiatric illness like severe depression, or severe language disturbances, particularly of receptive nature or with serious cognitive deficits (defined as equivalent to a mini-mental state exam score [MMSE] of 23 or less), or degenerative brain processes such as Alzheimer's disease - severe uncontrolled medical problems (e.g., cardiovascular disease, severe rheumatoid arthritis, active joint deformity of arthritic origin, active cancer or renal disease, any kind of end-stage pulmonary or cardiovascular disease, or a deteriorated condition due to age, uncontrolled epilepsy or others), more than moderate to severe microangiopathy, polyneuropathy, diabetes mellitus, or ischemic peripheral disease - problems with movement of the hands - receiving drugs acting primarily on the central nervous system, which lower the seizure threshold, such as antipsychotic drugs (chlorpromazine, clozapine) or tricyclic antidepressants (for the TMS component only) - pregnant (for the MRI component only) - medical or technical contraindications to MRI procedures or devices producing artifacts that impair MRI signal (e.g., pacemakers, implanted medication pumps, cochlear devices, neural stimulators, metal in the cranium, surgical clips, and other metal/magnetic implants, claustrophobia)