PHASE-DEPENDENT EFFECTS OF VERY SLOW-FREQUENCY TRANSCRANIAL ALTERNATING CURRENT STIMULATION OVER THE HAND REGION OF THE M1 OR SMA ON DECISION-MAKING DURING A GO/NOGO TASK

The movement-related cortical potential (MRCP) is a very slow negative cortical activity originating from the primary motor cortex (M1) and the supplementary motor area (SMA). MRCP reflects neural processes such as decision-making and motor preparation. MRCP is observed in both self-initiated and externally triggered movements. Although very slow-frequency transcranial alternating current stimulation (VS-tACS) mimicking MRCP applied to the M1 or the SMA modulates the timing of self-initiated movements. However, its effect on externally triggered movements remains unclear.
We examined phase-dependent effects of VS-tACS applied to the hand region of M1 or the SMA on motor responses during a Go/NoGo task. 50 healthy participants were randomly assigned to two experiments (n = 25 each). Participants performed the right index finger abduction in response to Go cues. Visual cues (80% Go, 20% NoGo) were presented randomly during the anodal or cathodal phase of VS-tACS. VS-tACS was delivered below perceptual threshold (≤ peak to peak 2 mA) at 0.125 Hz. Reaction time (RT), number of errors, and speed–accuracy trade-off (SAT) scores were analyzed.
VS-tACS applied to the hand region of M1 significantly modulated RT in a phase-dependent manner, with slower RT during the anodal phase, accompanied by changes in SAT scores. In contrast, VS-tACS applied to the SMA did not affect motor responses. These findings indicate stimulation site-specific effects of VS-tACS and suggest that VS-tACS over the hand region of the M1 may promote a more cautious response strategy by modulating decision-related processes.