Neuroscientists have discovered that memories are converted into permanent memories during sleep, and a new study from NYU Grossman School of Medicine proposes a mechanism to determine which memories are important enough to linger in the brain. The study focuses on brain cells called neurons that fire together in rhythmic cycles of sharp wave-ripples, which encode complex information essential for memory formation. The study found that events followed by a high number of sharp wave-ripples during the day are replayed more during sleep, leading to the consolidation of permanent memories.
Sharp wave-ripples are the physiological mechanism used by the brain to decide what memories to keep and discard. The brain computation switches into an idle re-assessment mode during pauses after experiencing something, leading to the formation of sharp wave-ripples. These reactivated neuronal patterns during post-task sleep contribute to the consolidation of memories. The firing of hippocampal “place cells” during sharp wave-ripples encodes the environment we are in, and during sleep, these cells fire rapidly, playing back the recorded event thousands of times to strengthen connections between cells.
The study tracked maze runs of mice using electrodes to record the firing of hippocampal cells during waking pauses and post-task sleep. The consumption of a reward after each maze run prepared the brain for sharp wave-ripples to occur. The research team recorded up to 500 neurons simultaneously in the hippocampus using dual-sided silicon probes, creating complex data that required dimension reduction to visualize neuronal activity intuitively and form hypotheses. Understanding the mechanisms by which the brain tags memories to become permanent may lead to the development of devices or therapies to adjust sharp wave-ripples for memory improvement.
The study’s authors from the Neuroscience Institute at NYU Langone Health, along with collaborators from the Center for Neural Science at New York University and the Quebec Artificial Intelligence Institute, conducted research supported by National Institute of Health grants. Future research may reveal ways to adjust sharp wave-ripples to enhance memory and potentially reduce the recall of traumatic events. The evolution of such a system remains a mystery, but further investigations could lead to significant advancements in memory research and potential therapeutic interventions. The findings shed light on the complex processes involved in memory consolidation during sleep and the role of sharp wave-ripples in determining which memories are retained in the brain.
