Faculty Opinions recommendation of Engrams and circuits crucial for systems consolidation of a memory.

Episodic memories initially require rapid synaptic plasticity within the hippocampus for their formation and are gradually consolidated in neocortical networks for permanent storage.However, the engrams and circuits that support neocortical memory consolidation remain unknown.We found that neocortical prefrontal memory engram cells, critical for remote contextual fear memory, were rapidly generated during initial learning via inputs from both hippocampal-entorhinal cortex and basolateral amygdala.After their generation, the prefrontal engram cells, with support from hippocampal memory engram cells, became functionally mature with time.Whereas hippocampal engram cells gradually became silent with time, engram cells in the basolateral amygdala, which were necessary for fear memory, are maintained.Our data provide new insights into the functional reorganization of engrams and circuits underlying systems consolidation of memory.Memories are thought to be initially stored within the hippocampal-entorhinal cortex (HPC-EC) (recent memory) and over-time are slowly consolidated within the neocortex for permanent storage (remote memory) (1-7).Systems memory consolidation models suggest that the interaction between the HPC-EC and the neocortex during and after an experience is crucial (8-12).Experimentally, prolonged inhibition of hippocampal or neocortical networks during the consolidation period produces deficits in remote memory formation (13-15).However, little is known regarding specific neural circuit mechanisms underlying the formation and maturation of neocortical memories through interactions with the HPC-EC network.By employing activity-dependent cell labeling technology (16-18) combined with viral vector-based transgenic, anatomical (19, 20), and optogenetic strategies (19, 21) for