Every day, our brain takes countless fleeting experiences — from walks on the beach to presentations at work — and transforms them into long-term memories. How exactly this works remains a mystery, but neuroscientists believe that it involves a phenomenon called neural replay, in which neurons rapidly recreate the same activation sequences that occurred during the original experience. Surprisingly, neural replays can happen both before and after an experience, suggesting they help in both memory storage and also future planning.
In a new study, neuroscientists at the University of California, Berkeley, recorded activity from hundreds of neurons simultaneously in freely flying bats. It is the first time that an ensemble of neurons — rather than just individual neurons — have been studied in concert in bats as they fly around and behave naturally. The data provided surprising new insights into neural replay and theta sequences, another phenomenon which is believed to be involved in memory and planning.
“For the past 20 years, we’ve been recording single neurons in bats and asking the question, ‘When animals are doing interesting things, what do individual neurons do?’” said study senior author Michael Yartsev, an associate professor of neuroscience and bioengineering and a Howard Hughes Medical Institute Investigator at UC Berkeley. “But in the brain, there are emerging properties that you only see when you’re looking at ensembles of neurons. In this study, we looked at these two phenomena — replay and theta sequences — that are only visible when you track many neurons at the same time.”
Better understanding the role of replay and theta sequences in the brains of animals could shed light on how long-term memories are formed and stored in humans, potentially leading to new treatments for neurological disorders like Parkinson’s disease and Alzheimer’s.
The study, which was published online today (July 9) in the journal Nature, was supported by grants from the Air Force Office of Scientific Research, the National Institute of Neurological Disorders and Stroke and the Office of Naval Research.