LAUSR

Experiences need to be tagged during learning for further consolidation. However, neurophysiological mechanisms that select experiences for lasting memory are not known. By combining large-scale neural recordings in mice with dimensionality reduction techniques, we observed that successive maze traversals were tracked by continuously drifting populations of neurons, providing neuronal signatures of both places visited and events encountered. When the brain state changed during reward consumption, sharp wave ripples (SPW-Rs) occurred on some trials, and their specific spike content decoded the trial blocks that surrounded them. During postexperience sleep, SPW-Rs continued to replay those trial blocks that were reactivated most frequently during waking SPW-Rs. Replay content of awake SPW-Rs may thus provide a neurophysiological tagging mechanism to select aspects of experience that are preserved and consolidated for future use. Editor’s summary In everyday life, there are many potential events to be remembered. However, only a small fraction are retained. Simultaneously recording large numbers of neurons from the hippocampus, Yang et al. found that their population activity differentiated not only the position of the animal in a maze but also the exact trial number in a memory task. After some trials, sharp wave ripples (SPW-Rs) occurred during reward consummation. The spike content of these SPW-Rs replayed the population activity during the maze run on that trial. Later, SPW-Rs occurred during non–rapid eye movement sleep, and these sleep SPW-Rs replayed mainly the sequences that were tagged by the waking SPW-Rs in the maze. This is a candidate tagging mechanism that determines which waking experience(s) will undergo long-term consolidation. —Peter Stern Hippocampal sharp wave ripples in the awake animal select events to be remembered by selectively consolidating them during sleep.