Artificial Association of Pre-stored Information to Generate a Qualitatively New Memory

• Context exposure and foot shock form cell ensembles in the CA1 and the BLA
• Synchronous activation of the ensembles artificially associates less-linked episodes
• The artificial association requires activation of both the CA1 and the BLA
• The artificial and physiological associations share the same molecular mechanisms

SummaryMemory is thought to be stored in the brain as an ensemble of cells activated during learning. Although optical stimulation of a cell ensemble triggers the retrieval of the corresponding memory, it is unclear how the association of information occurs at the cell ensemble level. Using optogenetic stimulation without any sensory input in mice, we found that an artificial association between stored, non-related contextual, and fear information was generated through the synchronous activation of distinct cell ensembles corresponding to the stored information. This artificial association shared characteristics with physiologically associated memories, such as N-methyl-D-aspartate receptor activity and protein synthesis dependence. These findings suggest that the association of information is achieved through the synchronous activity of distinct cell ensembles. This mechanism may underlie memory updating by incorporating novel information into pre-existing networks to form qualitatively new memories.

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