# Deconstruction of a Memory Engram Reveals Distinct Ensembles Recruited at Learning

## TL;DR

This study shows that specific groups of brain cells form and store fear memories during learning, with distinct roles in memory formation and recall.

## Contribution

The study identifies non-overlapping ensembles in the dorsal CA1 that form the core fear engram with precise temporal tagging.

## Key findings

- Non-overlapping dorsal CA1 ensembles are differentially active during fear memory acquisition.
- Cells linked to specific learning periods alone can drive memory expression and engram formation.
- The study reveals which ensembles are essential for memory formation and recall.

## Abstract

How are associative memories formed? Which cells represent a memory, and when are they engaged? By visualizing and tagging cells based on their calcium influx with unparalleled temporal precision, we identified non-overlapping dorsal CA1 neuronal ensembles that are differentially active during associative fear memory acquisition. We dissected the acquisition experience into periods during which salient stimuli were presented or certain mouse behaviors occurred and found that cells associated with specific acquisition periods are sufficient alone to drive memory expression and contribute to fear engram formation. This study delineated the different identities of the cell ensembles active during learning, and revealed, for the first time, which ones form the core engram and are essential for memory formation and recall.