High Definition Transcranial Direct Current Stimulation Does Not Modulate Implicit Task Sequence Learning and Consolidation.

The incidental acquisition of a succession of tasks is termed implicit task sequence learning. Patients with dorsolateral prefrontal cortex (DLPFC) lesions are strongly impaired in this ability. However, recent results of conventional transcranial direct current stimulation (tDCS) above the prefrontal cortex showed no modulation of implicit task sequence learning and consolidation. One explanation for these null findings is that conventional tDCS has non-focal effects on the cortex. Thus, the aim of the present study was to use a focal type of tDCS, namely high definition tDCS (HD-tDCS), to influence implicit task sequence learning and consolidation. Participants received stimulation during implicit task sequence learning and, 24 h later, consolidation was measured. The results showed that sequence learning was present in all conditions and sessions. Furthermore, consolidation was robust. However, both sequence learning and consolidation were not modulated by stimulation. Thus, this study corroborates previous findings by showing that even focal HD-tDCS is not sufficient to modulate implicit task sequence learning and consolidation.