No consistent effect of cerebellar transcranial direct current stimulation (tDCS) on visuomotor adaptation

Cerebellar transcranial direct current stimulation (ctDCS) is known to enhance adaptation to a novel visual rotation (visuomotor adaptation) and it is suggested to hold promise as a therapeutic intervention. However, it is unknown whether this effect is robust across varying task parameters. This question is crucial if ctDCS is to be used clinically, as it must have a consistent and robust effect across a relatively wide range of behaviours. The aim of this study was to examine the effect of ctDCS on visuomotor adaptation across a wide range of task parameters which were systematically varied. Therefore, 192 young healthy individuals participated in one of seven visuomotor adaptation experiments either in an anodal or sham ctDCS group. Each experiment examined whether ctDCS had a positive effect on adaptation when a unique feature of the task was altered: position of the monitor, offline tDCS, use of a tool, and perturbation schedule. Although we initially replicated the previously reported positive effect of ctDCS on visuomotor adaptation, this was not maintained during a second replication study, or across a large range of varying task parameters. At the very least, this may call into question the validity of using ctDCS within a clinical context where a robust and consistent effect across behaviour would be required.