Anterior basolateral amygdala neurons comprise a remote fear memory engram

Area of Science:

• Neuroscience
• Memory Research
• Behavioral Science

Background:

• Threatening environmental cues establish enduring fear memories.
• Fear memory recall involves reactivation of neuronal ensembles across brain regions.
• The persistence of anatomically specific neuronal ensembles in long-term fear memory is under investigation.

Purpose of the Study:

• To investigate the persistence and reactivation of neuronal ensembles in the anterior basolateral amygdala (aBLA) during remote fear memory recall.
• To determine if the size of these neuronal ensembles correlates with fear behavior.

Main Methods:

• Utilized TRAP2 and Ai14 mice to label Fos-activated neurons in the aBLA during fear conditioning.
• Assessed neuronal ensemble reactivation (tdTomato+ and Fos+) during remote memory recall three weeks later.
• Quantified ensemble sizes and correlated them with freezing behavior.

Main Results:

• Larger neuronal ensembles (TRAPed, Fos+, reactivated) were observed in fear-conditioned mice compared to context-conditioned mice.
• The middle sub-region and middle/caudal dorsomedial quadrants of the aBLA showed the highest densities of these ensembles.
• Freezing behavior during recall was not correlated with the size of the neuronal ensembles.

Conclusions:

• A fear memory engram, including the aBLA, persists at a remote time point.
• Fear memory recall and behavior are driven by plasticity in electrophysiological responses of engram neurons, not their population size.
• This suggests a mechanism for long-term fear memory encoding beyond simple ensemble size.