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

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