Although the positive influence of sleep on cognitive function has been recognised for some time, researchers at Baycrest have now discovered that a good night’s sleep may do more than preserve memory – it may actively enhance it. Their findings are the first to show that sleep protects memories and improves our ability to recall the sequence of life events, even more than a year later.
“While aspects of memory such as object size and colour tend to deteriorate over time, sleep appears to sharpen our memory for the order of experiences,” explains Dr Brian Levine, Senior Scientist at the Rotman Research Institute, part of the Baycrest Academy for Research and Education (BARE), and senior author of the study. Their research, titled “Sleep selectively and durably enhances memory for the sequence of real-world experiences,” was recently published in Nature Human Behaviour. According to Dr Levine, these results deepen our understanding of sleep’s critical role in weaving our experiences into lasting memories.
Unlike many memory studies, which typically require participants to memorise words or images under controlled laboratory conditions, this research introduced a highly novel and immersive real-world experience. Dr Levine, working alongside then-graduate students Dr Nicholas B. Diamond and Dr Stephanie Simpson, designed a 20-minute audio-guided tour featuring a series of artworks displayed at Baycrest, a globally renowned ageing and brain health centre in Toronto, Ontario. Participants completed the tour and were tested on their memory at intervals ranging from one hour to fifteen months after the experience. Tests measured both recall of the artworks’ physical features and the sequence of tour items. Notably, while memory for physical characteristics declined over time, sleep substantially boosted participants’ ability to recall the sequence of events.
To further validate their findings, the researchers conducted a second study where participants were randomly assigned to either a sleep or wake group. Those in the sleep group completed the tour and an initial memory test in the evening, followed by a night in a sleep laboratory where their brain activity was monitored through electroencephalography (EEG). They then took a second memory test the next morning. In contrast, the wake group toured and tested in the morning and underwent their second memory assessment in the evening after a full day of typical activities. Both groups participated in additional memory tests one week, one month, and fifteen months after the initial experience to measure the long-term effects of sleep on memory retention.
The results of the studies were striking. Sleep significantly enhanced memory for the sequence of the tour items, an advantage that was detectable after just a single night and remained evident even fifteen months later. However, sleep did not provide similar benefits for the memory of the artworks’ features, such as their shape or colour, which continued to decline over time. Brain wave recordings revealed that specific neural activity during deep sleep – particularly the presence of slow waves and sleep spindles – was associated with greater overall memory enhancement, suggesting a neurophysiological basis for these improvements.
This research reinforces the vital role of sleep as a foundation of good health, not only for physical well-being but for cognitive resilience as well. It highlights how deep sleep bolsters explicitly our ability to remember the chronological structure of daily events, even as finer details inevitably fade. These findings may also offer insights into the memory challenges older adults face, particularly those living with dementia, where disruption of deep sleep could contribute to difficulties in recalling life sequences. “The impact of sleep on memory is truly profound; even one night of good sleep can create lasting memory benefits that persist for over a year,” said Dr Levine.
More information: Brian Levine et al, Sleep selectively and durably enhances memory for the sequence of real-world experiences, Nature Human Behaviour. DOI: 10.1038/s41562-025-02117-5
Journal information: Nature Human Behaviour Provided by Baycrest Corporate Centre for Geriatric Care
