Fig. 2 |. Preventing and inducing ecphory by direct manipulation of fear memory engrams.

a, In this experiment¹⁹, neuronal ensembles in the CA1 region of the hippocampus were tagged with the inhibitory opsin, ArchT, during contextual fear conditioning (left). When placed back into the training context (i.e., the retrieval cue), mice froze (middle). However, optogenetic inhibition of the tagged ensemble during this test reduced freezing levels (right), indicating that engram silencing can prevent ecphory even in the presence of natural retrieval cues. b, In this experiment²⁶, neuronal ensembles in the DG region of the hippocampus were tagged with the excitatory opsin, ChR2, during contextual fear conditioning (left). When placed into a distinct context, mice did not freeze (middle). However, optogenetic activation of the tagged ensemble during this test induced freezing (right), indicating that engram activation, in the absence of natural retrieval cues, can induce ecphory.