Parietal tDCS and tactospatial working memory: Evidence for a behavioral benefit in a sham-controlled crossover study

The posterior parietal cortex (PPC) contributes to spatial working memory (WM), but whether parietal transcranial direct current stimulation (tDCS) can modulate tactospatial WM remains unclear. Thirty-two adults completed a double-blind, sham-controlled, within-subject crossover study with two counterbalanced visits comprising baseline, intervention, and post-intervention phases of a retro-cued tactospatial delayed match-to-sample task. During the intervention phase, active tDCS (2mA, 15min) or sham tDCS (30-s ramp-up followed by ramp-down) was applied with a left-parietal anode and right-supraorbital cathode. A sliding-window analysis identified a temporally localized Active-Sham improvement during the later part of the task. This contrast was significant under the hypothesized directional test (p = 0.041), but not under two-sided testing across the primary temporal search interval (p = 0.083). A supplementary analysis using narrower common temporal bounds yielded a significant two-sided result. The corresponding condition difference was not significant when averaged across the complete intervention phase. Baseline accuracy was negatively associated with the selected stimulation response (r = -0.327), consistent with the directional hypothesis, although this relationship and the covariate-adjusted analyses did not reach significance under two-sided testing. Together, these findings point to a possible behavioral benefit of parietal tDCS in tactospatial WM, while indicating that its magnitude, temporal characteristics, and relationship with baseline performance require further confirmation.