Concurrent-not independent-M1 anodal and cerebellar cathodal tDCS enhances skill acquisition of a dexterous rhythmic-timing video game.

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that can alter the excitability of targeted brain regions and influence motor learning. For the first experiment, we studied the effects of several individual stimulation montages (2 mA) on motor learning in a complex rhythm-timing video game task [n = 79, M1 anodal tDCS (M1 a-tDCS), cerebellar anodal tDCS (CB a-tDCS), cerebellar cathodal tDCS (CB c-tDCS), and SHAM]. Performance was assessed using a performance index (PI) incorporating keystroke timing accuracy, tap distribution ratio, and key error rate. All groups demonstrated significant improvements in PI (P < 0.001), but no significant interaction effect of tDCS group by practice block was observed. However, a nonsignificant trend toward improved PI scores was observed in both the M1 a-tDCS and CB c-tDCS groups, which led us to perform a second experiment using the same video game task, but with concurrent M1 anodal and cerebellar cathodal tDCS (n = 24, M1a + CBc tDCS). With concurrent stimulation, there was a significant main effect of stimulation group on PI gain scores across practice blocks (P = 0.021), with M1a + CBc showing greater gains than SHAM. When controlling for baseline performance, the M1a + CBc group had significantly higher posttest PI scores compared with the sham group (P = 0.034). The results of this study suggest concurrent M1a + CBc stimulation causes neuroplastic changes between M1 and the cerebellum that enhance motor learning in complex tasks beyond what single-site stimulation can provide.NEW & NOTEWORTHY Through a series of many different stimulation conditions and two experiments, we were able to demonstrate the significance of multisite transcranial direct current stimulation on skill learning of a complex task. What started out with testing several single stimulation montages eventually led to discovering the compounding benefit of doing two sites at once. We believe this will be the future of neuromodulation, as protocols become increasingly more efficient based on the motor tasks used.