Upper extremity motor impairment is one of the major sequelae of stroke, resulting in limitation of activities of daily livings. Noninvasive neuromodulation is one of the therapies for motor recovery, which includes transcranial magnetic stimulation and transcranial direct current stimulation(tDCS). Anodal tDCS increases excitability and cathodal tDCS decreases excitability of neurons.

In systematic reviews, tDCS applied over primary motor cortex showed positive results on motor learning and improvements of hand fine motors. Recently, there has been trials of tDCS over cerebellum, considering the connectivity of primary motor cortex and cerebellum in motor controls. However, the results of these trials are yet contradictory, and the study using the functional near infrared spectroscopy to prove the effects of tDCS over distant area is lacking.

Therefore, in this study, we used functional near infrared spectroscopy (fNIRS) to observe the hemodynamic change of primary motor cortex when applying tDCS over cerebellum ascertain their connectivity.

In this crossover design, participants are randomly allocated to "sham tDCS-washout period-anodal tDCS group" or "anodal tDCS- washout period- sham tDCS group". The recording of fNIRS starts 3 minutes before the tDCS stimulation and continues throughout 20 minutes of stimulation, until 30 minutes after the stimulation cessation. After 7 days of washout period, second recording is done as the same protocol. Outcome measures are the changes of concentration of deoxyhemoglobin [deoxy-Hb] and oxyhemoglobin [oxy-Hb].

Inclusion Criteria:

• Age: 19 years or older
• No known brain disorders

Exclusion Criteria:

• Uncontrolled or unstalbe medical condition
• Pregnant
• Scalp problem which interferese with tDCS
• metals in the head (example: clip, coil), cochlear implants

We are not planning to share the individual data publicly.