Abstract
Previous research has shown that the supplementary motor area (SMA) plays a critical role in the inhibition of movement. Recently it was shown that applying non-invasive transcranial direct current stimulation (tDCS) over the SMA affected participants' ability to inhibit their movement in a stop-signal reaction time task (Hsu et al. 2011). It was of interest in the current study whether modulating SMA excitability using tDCS would have similar effects in a stop-signal anticipation-timing task. Participants performed 2 sessions each consisting of both a pre- and post-test block of 160 trials in which they were instructed to extend their wrist concurrently with the arrival of a pointer to a target (i.e., a clock hand reaching a set position). In 20% of trials (stop trials) the pointer stopped 80, 110, 140, 170, or 200 ms prior to the target, and on these trials participants were instructed to inhibit their movement if possible. Anodal and cathodal tDCS sessions were applied for each participant, separated by at least 48 hours, between the pre- and post-tests. No change in the proportion of successfully inhibited movements on stop trials was found in post-tests for either tDCS polarity compared to pre-test (all p's > .05). However, anodal tDCS resulted in the early onset of movements in control trials with respect to the target (p = .028). These results suggest that the SMA may not have a crucial role in inhibiting anticipated movements, but may be more involved in initiation.Acknowledgments: Supported by NSERC