Brain-wide mapping reveals that engrams for a single memory are distributed across multiple brain regions

Area of Science:

• Neuroscience
• Memory Research
• Systems Neuroscience

Background:

• Memory engrams, the physical traces of memory, are traditionally localized to specific brain regions like the hippocampus.
• The unified engram complex hypothesis proposes that memories are stored across distributed, interconnected brain regions.

Purpose of the Study:

• To investigate the distributed nature of memory engrams for contextual fear conditioning.
• To create a partial map of the unified engram complex in mice.

Main Methods:

• Characterized encoding-activated neuronal ensembles in 247 brain regions using tissue phenotyping.
• Developed an engram index to identify high-probability engram regions (117 regions identified).
• Utilized optogenetic and chemogenetic manipulations for brain-wide neuronal ensemble reactivation.

Main Results:

• Identified a partial map of the engram complex for contextual fear memory.
• Found that many engram ensembles are functionally connected to hippocampal and amygdala engrams.
• Demonstrated that simultaneous reactivation of multiple engram ensembles significantly enhanced memory recall compared to single ensemble reactivation.

Conclusions:

• The findings support the unified engram complex hypothesis for memory storage.
• Memory recall involves the coordinated activity of distributed neuronal ensembles across multiple brain regions.