Short duration event related cerebellar TDCS enhances visuomotor adaptation

Background
Transcranial direct current stimulation (TDCS) is typically applied before or during a task, for periods ranging from 5 to 30 min.

Hypothesis
We hypothesise that briefer stimulation epochs synchronous with individual task actions may be more effective.

Methods
In two separate experiments, we applied brief bursts of event-related anodal stimulation (erTDCS) to the cerebellum during a visuomotor adaptation task.

Results
The first study demonstrated that 1 s duration erTDCS time-locked to the participants’ reaching actions enhanced adaptation significantly better than sham. A close replication in the second study demonstrated 0.5 s erTDCS synchronous with the reaching actions again resulted in better adaptation than standard TDCS, significantly better than sham. Stimulation either during the inter-trial intervals between movements or after movement, during assessment of visual feedback, had no significant effect. Because short duration stimulation with rapid onset and offset is more readily perceived by the participants, we additionally show that a non-electrical vibrotactile stimulation of the scalp, presented with the same timing as the erTDCS, had no significant effect.

Conclusions
We conclude that short duration, event related, anodal TDCS targeting the cerebellum enhances motor adaptation compared to the standard model. We discuss possible mechanisms of action and speculate on neural learning processes that may be involved.