Social reactivation of fear engrams enhances memory recall

Abstract

Significance Social interactions can bolster and protect memory performance. However, the relationship between social stimuli and individually learned memories remains enigmatic. Our work reveals that exposure to a stressed, naïve nonfamiliar conspecific or to the ambient olfactory–auditory cues of a recently stressed familiar conspecific induces reactivation of the cellular ensembles associated with a fear memory in the hippocampus. Artificially stimulating the hippocampal ensemble active during the social experience induces fearful behaviors in animals that have previously acquired a negative memory, revealing the interaction between individual history and social experience. The neural resurgence of fear-driving ensembles during social experiences leads to a context-specific enhancement of fear recall. Our findings provide evidence that unlike direct stressors, social stimuli reactivate and amplify an individual’s memories.

Natural forgetting reversibly modulates engram expression

“…Moreover, these reactivated cells were shown to be a functional component of the initially encoded memory as the direct modulation of engram activity via optogenetic stimulation or inhibition either facilitated or prevented the recall of an object memory. These findings are in support of previous work which has shown that engram activation is associated with the level of memory recall (2,46,53,54). In addition, they support a role for the hippocampus in object memory retrieval (55,56).…”

“…Altered (55). These findings are also in agreement with the current literature which has shown that engram activation is associated with the level of memory recall (1,46,(55)(56)(57). In addition, they also support a role for the hippocampus as a fundamental structure for object memory (58,59).…”

“…Our results showed that forgetting could be reversed following a brief reminder experience, which was associated with a corresponding increase in engram activity. Previous work from both human and rodent behavioral studies have shown that a brief exposure to reminder cues can aid memory recall (44–46). We further demonstrated that forgetting could be accelerated following repeated exposure to the training environment, therefore signaling the updated irrelevance of the object memory.…”

Memory circuits in dementia: The engram, hippocampal neurogenesis and Alzheimer’s disease

“…Together, their studies show that socially rewarding and socially stressful situations modulate memory retrieval, use different populations of abGCs, and have distinct effects on neuronal activity in the DG. Finkelstein et al (2022) examined the effect that social interactions have on memory. They focused on the hippocampus and amygdala, which are both involved in memory formation and social behavior learning and memory formation ( Bliss and Lomo, 1973 ; Kandel and Tauc, 1965 ).…”

Engram Stability and Maturation During Systems Consolidation Underlies Remote Memory

“…CreER can be expressed virally or in transgenic mice. Since 4-OHT leaves the body within a few hours, the labeling time window is significantly more precise than that of other methods such as the DOX-based system which is approximately a day long (5,(24)(25)(26). The use of these methods combined with immunohistochemistry (IHC) staining at the second time point in the memory task enables the study of new questions regarding the stability of engrams in reactivation and in the transition between memory stages.…”