Altered fear engram encoding underlying conditioned versus unconditioned stimulus-initiated memory updating

Area of Science:

• Neuroscience
• Memory Research
• Fear Conditioning

Background:

• Post-retrieval extinction, unlike extinction alone, can erase fear memories.
• The precise mechanism by which fear engrams are modified during memory updating remains unclear.

Purpose of the Study:

• To investigate whether the coding pattern of original fear engrams is remodeled or inhibited during memory updating.
• To elucidate the role of engram cell reactivation in conditioned stimulus- and unconditioned stimulus-initiated memory updating.

Main Methods:

• Analyzing engram cell activity in the prelimbic cortex and basolateral amygdala during memory updating.
• Examining the dependency of memory updating on engram cell reactivation.
• Assessing the overlap between fear and extinction cells.

Main Results:

• Increased reactivation of engram cells was observed in the prelimbic cortex and basolateral amygdala during memory updating.
• Memory updating initiated by conditioned stimulus or unconditioned stimulus critically depends on engram cell reactivation in these brain regions.
• Memory updating led to greater overlap between fear and extinction cells, indicating altered fear engram encoding.

Conclusions:

• This study provides the first evidence for overlapping ensembles between fear and extinction cells.
• Functional reorganization of original engrams underlies conditioned stimulus- and unconditioned stimulus-initiated memory updating.
• Post-retrieval extinction actively remodels fear memory engrams rather than simply inhibiting them.