Improvement of episodic memory retention by a memory reactivation intervention across the lifespan: from younger adults to amnesic patients

Evidence for indirect strengthening through reactivation of contextually bound memories

Episodic memory is, by definition, associative; retrieving one event often triggers the recollection of another related event. Memory reactivation has been shown to strengthen reactivated memories, but its effects on related, non-reactivated memories remain unclear. This study investigated whether reactivation of a consolidated target memory could indirectly enhance the retention of peripheral information acquired in the same context. We hypothesized that reactivating a consolidated target memory would improve its retention and strengthen contextually associated memories. To test this, we conducted four experiments (n = 238) in which participants first learned face-name pairs (target memory) alongside everyday objects (peripheral memory). On Day 2, a subset of participants underwent a reactivation intervention using incomplete reminders of the target memory, while others received a control intervention. On day 3, memory performance for both the target and peripheral memories was assessed. Results revealed that reactivation significantly improved the retention of target and peripheral memories when acquired in the same context. However, when peripheral memories were learned in a different context, reactivation of the target memory did not produce the same indirect strengthening effect. These findings suggest that the indirect strengthening of consolidated memories through reactivation is context-dependent and may rely on the shared spatiotemporal acquisition context. This study provides new insights into the mechanisms of memory reactivation and its broader impact on related non-reactivated memories.

Memory persistence: from fundamental mechanisms to translational opportunities

Memory persistence is a double edge sword. Persistence of adaptive memories is essential for survival and even determines who we are. Neurodegenerative conditions with significant memory loss such as Alzheimer's disease, testify how defects of memory persistence have severe and irreversible effects on personality, among other symptoms. Yet, maintenance of overly strong maladaptive memories underlies highly debilitating psychiatric conditions including post-traumatic stress disorder, specific phobia, substance dependence and binge eating disorder. Here we review the neurobiological mechanisms supporting memory formation, persistence, inhibition and forgetting. We then shift the focus to how such mechanisms have been exploited to alter the persistence of laboratory-generated memories in human healthy volunteers as a proof of concept. Finally, we review the effect of behavioural and pharmacological interventions in anxiety and addiction disorder patients, highlighting key findings, gaps, and future directions for basic and translational research.

Improving memory for unusual events with wakeful reactivation

Memory consists of multiple processes, from encoding information, consolidating it into short- and long- term memory, and later retrieving relevant information. Targeted memory reactivation is an experimental method during which sensory components of a multisensory representation (such as sounds or odors) are ‘reactivated’, facilitating the later retrieval of unisensory attributes. We examined whether novel and unpredicted events benefit from reactivation to a greater degree than normal stimuli. We presented participants with everyday objects, and ‘tagged’ these objects with sounds (e.g., animals and their matching sounds) at different screen locations. ‘Oddballs’ were created by presenting unusual objects and sounds (e.g., a unicorn with a heartbeat sound). During a short reactivation phase, participants listened to a replay of normal and oddball sounds. Participants were then tested on their memory for visual and spatial information in the absence of sounds. Participants were better at remembering the oddball objects compared to normal ones. Importantly, participants were also better at recalling the locations of oddball objects whose sounds were reactivated, compared to objects whose sounds that were not presented again. These results suggest that episodic memory benefits from associating objects with unusual cues, and that reactivating those cues strengthen the entire multisensory representation, resulting in enhanced memory for unisensory attributes.