Emotional memory can persist strikingly long, but it is believed that not all its elements are protected against the fading effects of time. So far, studies of emotional episodic memory have mostly investigated retention up to 24h post-encoding, and revealed that central emotional features (items) are usually strengthened, while contextual binding of the event is reduced. However, even though it is known for neutral memories that central versus contextual elements evolve differently with longer passage of time, the time-dependent evolution of emotional memories remains unclear. Hypothetically, compared to neutral memories, emotional item memory becomes increasingly stronger, accompanied by accelerated decay of – already fragile – links with their original encoding contexts, resulting in progressive reductions in contextual dependency. Here, we tested these predictions in a large-scale study. Participants encoded emotional and neutral episodes, and were assessed 30 minutes (N = 40), one day (N = 40), one week (N = 39), or two weeks (N = 39) later on item memory, contextual dependency, and subjective quality of memory. The results show that, with the passage of time, emotional memories were indeed characterized by increasingly stronger item memory and weaker contextual dependency. Interestingly, analyses of the subjective quality of memories revealed that stronger memory for emotional items with time was expressed in familiarity, whereas increasingly smaller contextual dependency for emotional episodes was reflected in recollection. Together, these findings uncover the time-dependent transformation of emotional episodic memories, thereby shedding light on the ways healthy and maladaptive human memories may develop.
Time-dependent effects of cortisol on the contextual dependency of negative and neutral memories
