Ensembles and engrams in mouse cortical and sub-thalamic brain regions supporting context and memory recall

Area of Science:

• Neuroscience
• Behavioral Biology
• Cognitive Science

Background:

• Cellular ensembles form memory engrams during learning, reactivating for recall.
• Previous research often conflates contextual and cue-specific engrams, with limited exploration of sex differences.
• Understanding engram dynamics is crucial for dissecting associative learning mechanisms.

Purpose of the Study:

• To differentiate engrams encoding contextual information from those involved in cue-associated learning and recall.
• To investigate potential sex differences in engram formation and reactivation.
• To examine cellular activity patterns in specific brain regions during fear conditioning and extinction.

Main Methods:

• Auditory fear conditioning and activity-dependent tagging in mice.
• Quantification of cellular activity in the infralimbic prefrontal cortex (IL-PFC), prelimbic prefrontal cortex (PL-PFC), and zona incerta (ZI).
• Analysis of neural ensembles during context exposure, fear recall, extinction training, and extinction recall.

Main Results:

• Male mice exhibited larger active cell ensembles in the IL-PFC during context exposure.
• Female mice showed a higher proportion of IL-PFC cells active during fear memory recall, independent of context.
• Extinction engrams were reactivated more in the IL-PFC than contextual engrams across sexes; no sex differences were found in PL-PFC or ZI.

Conclusions:

• A clear distinction exists between engrams encoding contextual information and those related to cue-associated learning and recall.
• Significant sex differences are evident in the allocation and reactivation of neuronal ensembles and engrams.
• Findings contribute to a nuanced understanding of memory engram specificity and sex-based neural variations.