Whole-brain map: A single memory is split and stored in multiple connected brain regions

Innovative brain imaging studies have shown that "memory imprints," collections of neurons that encode memories, are widely distributed, including in previously unaware areas

A new study from MIT's Picower Institute for Learning and Memory provides the broadest and most rigorous evidence to date that the mammalian brain retains a single memory that occurs in a widely distributed, functionally intact environment.

Memory research pioneer Richard Semon predicted this "unified memory complex" more than a century ago, but realizing this new study's confirmation of his hypothesis would require the application of multiple newly developed techniques

"When it comes to memory storage, we're usually talking about the hippocampus or the cerebral cortex," said co-lead and co-corresponding author Diraj Roy

memory map

The team conducted an unbiased analysis of 247 brain regions in mice to map the regions involved in memory copying

The maps highlighted many areas predicted to be involved in memory, but many were not

The authors point out that, to be truly engram cells, neurons should be activated during both encoding and recall

The authors write: "These experiments not only revealed the activation of significant memory engrams in known regions of the hippocampus and amygdala, but also in numerous thalamic, cortical, midbrain and brainstem structures

memory operation

After ranking the regions most likely to be involved in the memory puzzle, the team performed several manipulations to directly test their predictions and determine how the complex regions of the memory puzzle work together

For example, they engineered mice so that cells activated by memory coding could also be controlled by flashing lights (a technique called "optogenetics")

"Remarkably, when optogenetically stimulated, all of these brain regions produced robust memory recall," the researchers observed

The team then showed how the different regions in the complex imprint are connected

Further experiments showed that optogenetic reactivation of engram complex neurons followed a pattern similar to that observed in natural memory recall

The meaning of distributed storage

By storing a single memory in such a wide range of complexity, the brain may make memory more efficient and resilient

"Different memory imprints may allow us to reconstruct memories more efficiently when we try to remember previous events (also in the original encoding, and different memory imprints may provide different information from the original experience)
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Second, In disease states, if some regions are damaged, distributed memory will allow us to remember previous events and, in a way, be more resistant to regional damage
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In the long term, a second thought might provide a clinical strategy for dealing with memory impairments: "If some memory impairments are caused by hippocampal or cortical dysfunction, then could we target memory engram cells that are understudied in other regions, Could such an operation restore some memory function?"

This is just one of many new questions researchers can ask, as this study has revealed the list of searches for at least one memory in the mammalian brain
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Reference: “Brain-wide mapping reveals that engrams for a single memory are distributed across multiple brain regions” by Dheeraj S.
Roy, Young-Gyun Park, Minyoung E.
Kim, Ying Zhang, Sachie K.
Ogawa, Nicholas DiNapoli, Xinyi Gu , Jae H.
Cho, Heejin Choi, Lee Kamentsky, Jared Martin, Olivia Mosto, Tomomi Aida, Kwanghun Chung and Susumu Tonegawa, 4 April 2022, Nature Communications .

DOI: 10.
1038/s41467-022-29384-4