Transcranial Direct Current Stimulation of Supplementary Motor Region Impacts the Effectiveness of Interleaved and Repetitive Practice Schedules for Retention of Motor Skills.

Interleaved rather than repetitive practice (RP) is associated with superior retention of motor skills. It has been argued that this results from improved post-practice consolidation reflected in greater offline gains following interleaved practice (IP). The magnitude of this offline benefit has been associated with greater recruitment of supplementary motor area (SMA) during encoding. The present study administered anodal or cathodal transcranial direct current stimulation (tDCS) during interleaved or RP respectively in an attempt to modify the activity at SMA and the concomitant retention outcomes commonly associated with these training formats. Sixty-nine participants were assigned to one of four experimental conditions that included: IP-sham, RP-sham, IP-cathodal tDCS, and RP-anodal tDCS. Real or sham stimulation at SMA was administered during practice of three unique 6-key discrete sequence production tasks which lasted approximately 20-min. Tests were administered prior to practice and immediately after practice as well at 6-h, 24-h, and 72-h after practice ended. As anticipated, IP resulted in poorer acquisition but superior offline gain. Enhanced offline gain following interleaved training resulted from rapid stabilization of performance within the first 6-h following encoding and overnight improvement that continued over multiple sleep episodes. Administration of anodal stimulation at SMA during RP improved performance during training compared to sham but this benefit was short lived as forgetting during the first 6-h after practice was consistent with that observed for the sham counterpart. However, supplementing RP with anodal stimulation at SMA did foster overnight offline performance gains not displayed by individuals that experienced RP in the absence of stimulation.