Within-session repeated a-tDCS: The effects of repetition rate and inter-stimulus interval on corticospinal excitability and motor performance

Abstract

ObjectiveThis study investigated the effect of rate and stimulation interval of anodal transcranial direct current stimulation (a-tDCS) on CSE and motor performance. MethodsTwelve healthy individuals participated in this study. CSE was assessed before and after five experimental conditions of one, two or three applications of 10min of a-tDCS with an interval of 5 or 25min. a-tDCS was applied with a constant current density of 0.016mA/cm2. Purdue pegboard-test was selected for motor performance assessment. ResultsCompared to single 10min stimulation, the magnitude of the within-session repeated a-tDCS induced excitability was enhanced significantly after the second stimulation was performed with an interval of 25min, but not 5min. However, by increasing the number of a-tDCS to three repetitions the CSE was significantly increased and lasted for 2h with both 5 and 25min intervals. Furthermore, CSE enhancement remained significant for up to 24h for within session a-tDCS repetitions with 25min intervals. Likewise, significant improvement was seen in motor performance following three times repetition with 25min inter-stimulus intervals. ConclusionsThe results suggest that within session repeated a-tDCS with longer intervals within the lasting effects of the previous stimulations are preferable for increasing induced excitability changes with longer lasting effects. Significance: It is of particular importance to increase the a-tDCS lasting effects to consolidate the neuroplastic CSE changes.