Transcranial direct current stimulation selectively improves temporal working memory

Temporal working memory (WM)-the ability to temporarily store and manipulate temporal information-is constrained by a storage capacity threshold of approximately 2-3 s. Transcranial direct current stimulation (tDCS), an emerging non-invasive intervention, holds potential for enhancing temporal WM. We investigated whether anodal tDCS over key WM regions (right prefrontal cortex, PFC; posterior parietal cortex, PPC) could improve temporal WM capacity specifically for durations exceeding the critical threshold. We used a matching-to-sample paradigm with sample durations encompassing the threshold (1, 2, 3, 4 s); improvement in temporal WM capacity was operationally defined specifically as enhanced accuracy for supra-threshold durations (3 and 4 s). Fifty-six healthy participants were randomly assigned to receive either actual or sham stimulation over PFC or PPC, and completed the matching-to-sample task once before and once immediately after stimulation. Results showed that anodal stimulation over the PFC selectively enhanced performance at the 3 s duration, with no significant effects at other durations or with PPC stimulation. These findings provide causal evidence underscoring the crucial role of the PFC-rather than the PPC-in supporting temporal WM, with the effect of the single-session tDCS protocol being specific to the 3 s duration, which represents the critical threshold point.