Rationale: When a consolidated memory is reactivated, it becomes labile and modifiable. Recently, updating of reactivated episodic memory was demonstrated by Hupbach et al. (Learn Mem 14:47-53, 2007). Memory updating involves two vital processes-reactivation followed by reconsolidation. Here, we explored effects of psychosocial stress on episodic memory updating. Based on prior research, we hypothesized that stress before reactivation or stress before reconsolidation would impair memory updating.
Methods: Participants learned a set of objects (list 1) on day 1. On day 2, some participants were reminded of list 1 before learning a second set of objects (list 2). Memory for list 1 was tested on day 3. Stress was administered either before reactivation of list 1 on day 2 (exp 1) or before reconsolidation of list 1, i.e., after reactivation and learning list 2 on day 2 (exp 2).
Results: Memory updating involves the incorporation of list 2 items into list 1 memory, contingent upon the reactivation of list 1 memory. In exp 1, the reminder groups had higher intrusions than the no-reminder groups, but contrary to our predictions, stress did not reduce this reminder effect. Stress effects were, however, found in exp 2: the reminder group that was stressed after reactivation and new learning showed fewer intrusions than the control reminder group.
Conclusion: The findings suggest that stress before reactivation does not impair memory updating but stress at the onset of reconsolidation can. Timing may determine the effects of stress on memory processing.