Researchers at Salk Institute for Biological Studies are attempting to explain how the brain manages to keep track of the hugely complicated environments that people navigate on a daily basis.
They discovered how the dentate gyrus, a subregion of the hippocampus, helps keep memories of similar events and environments separate.
The findings, which clarify how the brain stores and distinguishes between memories, may also help identify how neurodegenerative diseases, such as Alzheimer's disease, rob people of these abilities.
"Everyday, we have to remember subtle differences between how things are today, versus how they were yesterday - from where we parked our car to where we left our cellphone," Fred H. Gage, senior author on the paper and the Vi and John Adler Chair for Research on Age-Related Neurodegenerative Disease at Salk said.
"We found how the brain makes these distinctions, by storing separate 'recordings' of each environment in the dentate gyrus," he said.
The process of taking complex memories and converting them into representations that are less easily confused is known as pattern separation.
Computational models of brain function suggest that the dentate gyrus helps us perform pattern separation of memories by activating different groups of neurons when an animal is in different environments.
However, previous laboratory studies found that in fact the same populations of neurons in the dentate gyrus are active in different environments, and that the way the cells distinguished new surroundings was by changing the rate at which they sent electrical impulses.
This discrepancy between theoretical predictions and laboratory findings has perplexed neuroscientists and obscured our understanding of memory formation and retrieval.
The Salk researchers' findings suggest that recalling a memory-such as the location of missing keys-does not always involve reactivation of the same neurons that were active during encoding.
More importantly, the results indicate that the dentate gyrus performs pattern separation by using distinct populations of cells to represent similar but non-identical memories.
The findings help clarify the mechanisms that underpin memory formation and shed light on systems that are disrupted by injuries and diseases of the nervous system.
The study is published in the journal eLife.