Cerebellar tDCS on Motor Learning of Healthy Individuals

A crossover trial with healthy volunteers will be conducted. Three sessions will be performed with at least 48 hours washout period to minimize carry-over effects. In each session, volunteers will be submitted to: fatigue and attention levels evaluation, handwriting test, serial reaction time task (SRTT) before and after ctDCS conditions and after session, a performance perception evaluation.

A crossover, pseudo-randomized, sham-controlled and triple blind will be performed in order to evaluate ctDCS effects on motor learning, since evidence pointed to the crucial role of cerebellum on motor behavior. A non-involved research will conduct a pseudo-randomization (www.randomization.com) to warrant the counterbalanced sessions order and the allocation concealment. Volunteers, researchers and statistical analysis will be blinded to ctDCS condition.

After given prior informed consent, volunteers will be submitted to three experimental sessions: anodal ctDCS, cathodal ctDCS and sham ctDCS. Fatigue and attention levels, handwriting test and SRTT will be performed before and after stimulation. In addition, performance perception evaluation will be assessed at the end of session.

Electrical current will be delivered through a DC stimulator (NeuroConn Plus, Germany) using a pair of saline-soaked sponge electrodes (surface 35cm²). The active electrode (anode or cathode) will be placed over the left cerebellum (3 cm lateral to the inion) and the reference, over the left arm with current intensity of 2mA, fade in and fade out of 10 seconds, during 20 minutes. Sham tDCS has been used in several studies to evaluate active tDCS effects.

Sham ctDCS will be applied using the same electrodes placement and parameter settings of cathodal ctDCS however, stimulation will last only 30 seconds but volunteers will be with electrodes montage for 20 minutes. Because the device will be automatically turned off without volunteer's perception, early sensations (mild to moderate tingling) on stimulation site will be experienced without inducing any modulatory effects. Moreover, after each ctDCS session, an adverse effects questionnaire will be applied.

Fatigue and attention levels will be measured through an analogue scale graded from 0 to 10, where 0 means lower fatigue or attention levels and 10, the higher fatigue or attention levels.

Handwriting test: volunteers will be instructed to write six words with digital pen using the non-dominant hand on a tablet provided with analysis software system (MovAlyzer, EUA). The task will be performed spontaneously, without any instruction bias during writing activity. Each session has different word sequences but the difficulty level will be maintained (six words, two of them with 4, 6 and 8 letters).

SRTT: will be performed through software with visual stimuli presented on a computer screen in four different positions. Volunteer must press, with the non-dominant hand, a corresponding key with a predetermined finger as soon as possible when a highlighted star appears on the screen. The test comprises eight blocks with 120 trials each. Implicit motor learning is measured by performance changes between the blocks 5, 6 and 7.

Performance perception evaluation: in order to correlate stimulation type to the conscious improvement on motor task performance (SRTT and handwriting test) will be asked in the end of each session: "Regarding today's session, comparing your motor performance before and after cerebellar stimulation, you consider that you were better, worse or the same as before?"

Eligibility Criteria:
Inclusion Criteria:

* Right-handed (assessed by Edinburgh Handedness Inventory)
* Healthy volunteers (self report)
* Absence of neurological and psychiatric diseases
* No history of severe musculoskeletal injury on wrists and fingers
* Without using drugs or neuroactive substances regularly

Exclusion Criteria:

* Pregnancy
* Presence of metallic implant in close contact to the target stimulation area
* Acute eczema under the target stimulation area
* Pacemaker
* History of seizures or epilepsy
* Hemodynamic instability