Transcranial Direct Current Stimulation over the Posterior Parietal Cortex Increases Non-target Retrieval during Visual Working Memory

Accurate visual working memory (VWM) requires precise content-context binding. Previous studies have revealed a close relationship between the posterior parietal cortex (PPC) and feature binding during VWM, this study further examined their causal relationship through three transcranial direct current stimulation (tDCS) experiments. In Experiment 1 (N = 57), participants underwent three sessions of tDCS separately, including PPC stimulation, occipital cortex stimulation, and sham stimulation, and completed a series of delayed estimation tasks for orientations before and after stimulation. Results showed that tDCS over PPC selectively prolonged recall response time (RT) and increased the probability of non-target responses (a.k.a. failure of feature binding). In Experiment 2 (N = 29), combining metacognition estimation during the task, we further investigated whether the effects of PPC stimulation on RT and increased probability of non-target responses were attributed to more mis-binding (i.e., participants self-reported "remembered" in non-target responses) or informed guessing (participants self-reported "forgotten" in non-target responses). We replicated the main findings in Experiment 1, and we also observed greater tDCS effects of PPC on RT in informed guessing trials than mis-binding trials while comparable effects on non-target response rates in these two types of trials. In Experiment 3 (N = 28), we then examined whether the effects of tDCS over PPC specifically influenced the memory retrieval process by using a change detection task. We found that PPC stimulation did not influence the recognition RT or accuracy. Together, this study provides causal evidence supporting the involvement of PPC in feature binding during VWM retrieval. Significance StatementVisual working memory (VWM) enables humans to temporarily store and process visual information, which requires accurate binding of items to their unique context. Accumulating studies posited that the posterior parietal cortex (PPC) is closely related to this binding process, the current study further examined their causal relationship. Through three strictly within-subject well-designed non-invasive neural stimulation experiments, we found that PPC stimulation selectively increased response time (RT) and binding error during VWM. Moreover, we found these changes were modulated by individual metacognition and only occurred during memory recall instead of recognition. Together, our results provided strong evidence that PPC is causally involved in the binding process during visual working memory retrieval.