Effects of static transcranial magnetic stimulation over right parietal cortex on visuomotor adaptation


The parietal cortex is thought to play a crucial role in visuomotor adaptation. Recently, our laboratory has provided evidence that the parietal contribution to visuomotor adaptation may be lateralized, such that adaptation to perturbed visual feedback presented to the left of gaze may more strongly solicit the right parietal hemisphere and vice versa. The purpose of this study was to test this hypothesis with inhibitory static transcranial magnetic stimulation (STMS). Briefly, during an acquisition phase (200 trials) participants made reaching movements towards visual targets located either to the left or right of gaze while learning to compensate for a 30° visuomotor rotation. Implicit adaptation was then assessed with a retention test without online visual feedback. In the STMS group (N=9) a cylindrical neodymium magnet was positioned over the right parietal cortex, whereas in the placebo group (PLA, N=10), a non-magnetic nickel cylinder was placed over the same area. Given its position, it was hypothesised that STMS would selectively impair implicit adaptation to targets located to the left of gaze. Notably, our results refute this hypothesis, as retention was not significantly different between STMS and PLA at right or left target locations. During the last 40 trials of acquisition, however, STMS compensated for less of the visuomotor rotation compared to PLA (p=0.02), and this was solely true for targets located to the left of gaze. These preliminary findings suggest that the parietal hemisphere contralateral to visual feedback plays a role in compensating for, but not implicitly adapting to, a visuomotor rotation.