Transcranial direct current stimulation over posterior parietal cortex and temporoparietal junction improves contextual cueing.

Implicit contextual learning (ICL) refers to memory-guiding attention through spatial regularities that improve visual search performance, commonly known as contextual cueing. The posterior parietal cortex (PPC) is primarily associated with top-down, goal-directed (endogenous) attention, whereas the temporoparietal junction (TPJ) is involved in bottom-up, stimulus-driven (exogenous) attention. In this study, we examined the role of these regions in ICL using anodal transcranial direct current stimulation (atDCS), hypothesizing that PPC stimulation would facilitate goal-directed attentional focus, whereas TPJ stimulation would enhance performance during stimulus-driven reorienting to task-relevant cues. Sixty participants were randomly assigned to one of the three conditions: active stimulation over the right PPC or over the right TPJ, or sham condition. Each participant completed the ICL task following 20 min of 2.0 mA anodal or sham stimulation. Both right PPC and right TPJ stimulation enhanced ICL compared with the sham condition, with a more pronounced effect of the latter. Right PPC stimulation improved ICL comparably for targets in the contralateral (left) and ipsilateral (right) visual hemifields. In contrast, right TPJ stimulation produced a stronger overall effect and a dynamic, hemifield-specific pattern not observed with PPC stimulation. Specifically, right TPJ stimulation produced significantly greater contralateral ICL enhancement overall, but stronger ipsilateral facilitation during the first half of the experiment. Moreover, right TPJ stimulation was the only condition that significantly increased the number of participants exhibiting a positive ICL effect. These findings suggest that both the right PPC and the right TPJ contribute to ICL, with right TPJ stimulation eliciting a stronger and more distinct, hemifield-dependent influence on ICL than PPC stimulation.