Abstract
Cyclical bimanual movements can be characterized as in-phase (symmetrical) or anti-phase (asymmetrical) with these patterns representing elementary coordination dynamics. However, in-phase movements are more accurate and stable than anti-phase movements. If movement frequency is systematically increased during anti-phase movements, a spontaneous change (phase transition) to an in-phase pattern occurs (e.g., Kelso, 1984). Neurophysiological studies have provided converging evidence that supplementary motor area (SMA) plays a critical role in the successful performance of these patterns, especially during anti-phase movements (e.g., Serrien et al., 2002). The present experiment investigated how offline transcranial direct current stimulation (tDCS) applied over SMA affected the ability to maintain a stable relative phase. tDCS is a non-invasive neural stimulation technique that can increase (anodal) or decrease (cathodal) cortical excitability. Subjects performed metronome-paced trials of cyclical in-phase and anti-phase bimanual supination-pronation movements as oscillation frequency increased throughout each 56 s trial from 1.75 to 3.25 Hz in .25 Hz increments. Results showed no significant pre- and post-test differences for the in-phase pattern following anodal or cathodal tDCS. For the anti-phase pattern however, the mean relative phase between hands was significantly less errorful across all frequencies following anodal tDCS (p < .05). In contrast, relative phase performance at each frequency was unchanged following cathodal tDCS. These findings suggest increased activity in SMA induced by anodal tDCS can improve interlimb coordination during anti-phase patterns and adds to the accumulating evidence of the pivotal role of the SMA in bimanual coordination (e.g., Swinnen & Wenderoth, 2004).Acknowledgments: Supported by NSERC (ANC)