Memory is stored in distributed neuronal ensembles known as engrams, which are defined by their activation during encoding and their necessity for recall. Current research relies heavily on immediate-early gene (IEG) expression to map these traces; however, the temporal lag of transcription fails to account for the real-time processing of neural activity or the long-term structural remodeling required for memory persistence. In this review, we propose that the noncoding genome serves as the essential regulatory infrastructure of the engram, governing the transition from transient firing to stable physical change. We outline a 3-phase model of noncoding RNA (ncRNA) regulation: first, we discuss how synaptic microRNAs act as high-speed filters during encoding to gate excitability and potentially solve the IEG latency paradox. Second, we examine how long ncRNAs maintain epigenetic identity and valence during the interim state. Finally, we argue that consolidation involves a "pseudo-developmental" reactivation of neurogenic and synaptogenic programs driven by ncRNAs. This framework provides a unified perspective on how mature neurons multiplex diverse experiences, suggesting that ncRNAs are not merely accessory molecules but the central architects of memory maintenance, specificity, and stability.
Nanda et al. (Fri,) studied this question.