Sleep selectively and durably enhances memory for the sequence of real-world experiences

Sleep is thought to play a critical role in the retention of memory for past experiences (episodic memory), reducing the rate of forgetting compared with wakefulness. Yet it remains unclear whether and how sleep actively transforms the way we remember multidimensional real-world experiences, and how such memory transformation unfolds over the days, months and years that follow. In an exception to the law of forgetting, we show that sleep actively and selectively improves the accuracy of memory for a one-time, real-world experience (an art tour)-specifically boosting memory for the order of tour items (sequential associations) versus perceptual details from the tour (featural associations). This above-baseline boost in sequence memory was not evident after a matched period of wakefulness. Moreover, the preferential retention of sequence relative to featural memory observed after a night's sleep grew over time up to 1 year post-encoding. Finally, overnight polysomnography showed that sleep-related memory enhancement was associated with the duration and neurophysiological hallmarks of slow-wave sleep previously linked to sequential neural replay, particularly spindle-slow wave coupling. These results suggest that sleep serves a crucial and selective role in enhancing sequential organization in our memory for past events at the expense of perceptual details, linking sleep-related neural mechanisms to the days-to-years-long transformation of memory for complex real-life experiences.