Engram neurons: Encoding, consolidation, retrieval, and forgetting of memory

Abstract

Tremendous strides have been made in our understanding of the neurobiological substrates of memory – the so-called memory “engram”. Here, we integrate recent progress in the engram field to illustrate how engram neurons transform across the “lifespan” of a memory — from initial memory encoding, to consolidation and retrieval, and ultimately to forgetting. To do so, we first describe how cell-intrinsic properties shape the initial emergence of the engram at memory encoding. Second, we highlight how these encoding neurons preferentially participate in synaptic- and systems-level consolidation of memory. Third, we describe how these changes during encoding and consolidation guide neural reactivation during retrieval, and facilitate memory recall. Fourth, we describe neurobiological mechanisms of forgetting, and how these mechanisms can counteract engram properties established during memory encoding, consolidation, and retrieval. Motivated by recent experimental results across these four sections, we conclude by proposing some conceptual extensions to the traditional view of the engram, including broadening the view of cell-type participation within engrams and across memory stages. In collection, our review synthesizes general principles of the engram across memory stages, and describes future avenues to further understand the dynamic engram.

NMDA Receptors Control Activity Hierarchy in Neural Network: Loss of Control in Hierarchy Leads to Learning Impairments, Dissociation, and Psychosis

“…This study underscores an interesting fundamental question: why does the hippocampus need to develop a neural activity hierarchy? There are limited studies that have addressed such a question 13,16,21,46 . Possible explanations include: (1) A animal subject does not encounter all sorts of sensory stimuli at one time.…”

“…While certain proteins such as CREB 15,45 and potassium channels 22,46,47 are found to regulate intrinsic neuronal excitability affecting learning, memory encoding or retrieval, a real time neural activity hierarchy has not been quantitatively determined previously. Leveraging deep-brain in vivo calcium imaging acquired during freely behaving trace fear conditioning experiments, we sought to develop a method to measure a neural activity hierarchy and quantitatively establish primed neurons that participate in trace memory formation.…”

Dopamine-Modified Chitosan Patterning Hydrogel with Dynamic Information Storage Ability

“…Memory is the process of encoding, storing, and retrieving information . Dopamine (DA), a neurotransmitter, can strengthen connections between neurons and aid in encoding and storing memory.…”

“…Memory is the process of encoding, storing, and retrieving information. 20 Dopamine (DA), a neurotransmitter, can strengthen connections between neurons and aid in encoding and storing memory. Once the encoding and storage of the memory is complete, neurotransmitters can then activate neurons to induce information retrieval 21 (Scheme 1a).…”

Neuropeptide Y co-opts neuronal ensembles for memory lability and stability

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Memory engrams are formed by activity-dependent recruitment of distinct subsets of excitatory principal neurons (or neuronal ensembles) whereas inhibitory neurons pivot memory lability and stability [1][2][3][4][5] . However, the molecular logic for memory engrams to preferentially recruit specific type of interneurons over other subtypes remains enigmatic.

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