Single-pulse tms over the parietal cortex does not impair trial-by-trial adaptation


Whether the parietal cortex contributes to implicit adaptation of internal models remains unclear. Using electroencephalography, we recently reported increased parietal activity in response to an intermittently imposed visuomotor rotation as well as a directional reaching bias on the subsequent trial. This raised the possibility that the parietal cortex could contribute to the trial-by-trial movement adjustments that subtend implicit adaptation. The goal of the present study was to test whether the observed parietal responses were causally related to this type of learning. Participants reached toward visual targets while being pseudo-randomly submitted to a 45? visuomotor rotation. On half of all rotation trials, single-pulse transcranial magnetic stimulation (TMS) was applied over either the left (electrode P3; N = 14) or right (electrode P4; N = 14) parietal cortex 150 ms after visual feedback provision (i.e. the approximate timing of the parietal responses in our previous study). It was hypothesized that a directional reaching bias (i.e., trial-by-trial adaptation) would be lesser on trials that followed rotation with the TMS condition (i.e., when the parietal cortex was disrupted) as compared to no TMS. Consistent with our hypothesis, a potent directional reaching bias was observed on post-rotation trials (p ? 0.002), indicating that visuomotor rotation resulted in robust trial-by-trial adaptation. Contrary to our hypothesis, however, parietal stimulation did not significantly impact the post-rotation bias (p = 1.00). These results indicate that neural activity in parietal areas 150 ms after visual feedback provision is not critical for trial-by-trial adaptation, and thus possibly implicit adaptation.