Reactivating and reorganizing activity-silent working memory: two distinct mechanisms underlying pinging the brain

Recent studies have proposed that visual information can be maintained in an activity-silent state during working memory (WM), which can be reactivated by task-irrelevant high-contrast visual impulses (i.e., "pinging the brain"). Although pinging the brain has become a popular tool for exploring activity-silent WM in recent years, its underlying mechanisms remain unclear. In the current study, we directly compared the behavioral consequences and neural reactivation effects of context-independent and context-dependent pings to distinguish the noise-reduction and target-interaction hypotheses of pinging the brain. At first, in a behavioral study, we found that, compared with the baseline condition (no ping), only the horizontal context-dependent pings impaired recall performance. In a follow-up electroencephalogram study, our neural decoding results showed that the context-independent pings reactivated activity-silent WM transiently without changing the original WM representations or recall performance. In contrast, the context-dependent pings reactivated activity-silent WM more durably and further reorganized WM information by decreasing the dynamics of items neural representations. Notably, only the reactivation strength of the context-dependent pings correlated with recall performance and was modulated by the location of memorized items, with neural representations only being reactivated when both items and pings were presented horizontally. Together, our results provided evidence for two distinct mechanisms underlying pinging the brain, and the pings context played a critical role in reactivating and reorganizing activity-silent WM.