Newly Found Brain Activity Key to Sleep Memory Boost

A newly identified activity in the brain that occurs while we sleep – a barrage of action potentials, or a BARR – plays a crucial role in rebalancing the hippocampal neural network during memory consolidation. The findings offer fresh insights into how our brains preserve memories while maintaining stability, as we slumber. Memory consolidation – a process that stabilizes and strengthens our recent experiences into long-term memories – occurs when we sleep. During the non-rapid eye movement (NREM) phase of sleep, hippocampal neurons display short bursts of firing activity called sharp-wave ripples (SWRs). These patterns are known to be essential for memory consolidation. However, the mechanism by which the hippocampus rebalances its activity after this selective increase in firing rates is unknown. Using large-scale electrophysiology, Lindsay Karaba and colleagues studied neuronal activity in various areas of the hippocampus in mice and rats during learning tasks and during sleep. They discovered a new type of network event generated by a subset of CA2 pyramidal cells. A subset of CA2 cells fired long barrages of action potentials (BARRs) during NREM sleep. CA1 neurons that had increased their activity during learning were inhibited. After learning, disrupting BARRs using optogenetic manipulation led to impaired memory performance. This suggests that a balanced level of neuronal reactivation is essential for memory consolidation, and either too little or too much reactivation can lead to memory problems. BARRs appear to help maintain this balance, preventing excessive neuronal activity that could become pathological. "The discovery of BARRs reveals how hippocampal memory reactivation is delicately controlled in memory consolidation during sleep and offers a possible reconciliation between the memory reactivation theory and the synaptic downscaling theory," write Xiang Mou and Daoyun Ji in a related Perspective.