Flexible memory interplays: selective reactivation of long-term memories in working memory

Working memory is defined as the online storage space for ongoing tasks. It stores both newly encoded information and retrieved long-term memories. However, there is a growing amount of work to suggest that long-term memories can also guide behavior. This raises the question: Why do humans invest metabolic resources in reactivating long-term memories in working memory instead of guiding behavior directly via long-term memory? We conducted six experiments examining working memory reactivation of long-term memories in anticipation of task demands encompassing protection against interference, behavioral guidance, and adaptation to novel settings. Using behavioral and electrophysiological indices, we measured the extent to which long-term memories are reactivated in working memory in anticipation of these task demands relative to the anticipation of a recognition task, which constituted a baseline. Compared to this baseline, we found equal memory reactivation when anticipating perceptual interference and dual-task interference, and less memory reactivation when anticipating attentional guidance. On the other hand, reactivation was stronger for task switching, contextual changes, and performing mental operations. These results suggest that the reactivation of long-term memories in working memory is not primarily for protection against interference or behavioral guidance. Instead, stronger reactivation occurs when there is a need to update the memories themselves (i.e., perform a mental operation) or the settings in which they are used (i.e., the task rules and the context). This insight implies that the goal of reactivating long-term memories in working memory may be to facilitate adaptation to novel situations. Our research challenges influential memory models and recent empirical work that consider working memory as the default buffer for retrieved long-term memories and instead highlights a flexible and dynamic interplay between long-term memories and working memory.