Sleep does more than simply protect memory from fading—it actively enhances our ability to recall the order of life events, according to groundbreaking research from Baycrest’s Rotman Research Institute. The study, published in Nature Human Behaviour, is the first to demonstrate that sleep can improve memory for event sequences even after more than a year.
“While our memory for features such as object size and color declines over time, sleep can improve our memory for event sequence,” said Dr. Brian Levine, Senior Scientist at the Rotman Research Institute and senior author of the study. “This study deepens our understanding of how critical sleep is for integrating experiences into memory.”
The research stands out from traditional memory studies, which often involve participants memorizing isolated items in lab settings. Instead, Dr. Levine and co-authors Dr. Nicholas B. Diamond and Dr. Stephanie Simpson designed a real-world, immersive experience: a 20-minute audio-guided tour of an art exhibit at Baycrest, a global leader in aging and brain health based in Toronto.
Participants were tested on their memories of the tour’s sequence and visual details at intervals ranging from one hour to 15 months after the experience. The results were clear—while memory for visual details like color and shape declined over time, sleep consistently enhanced memory for the sequence of events.
To further confirm their findings, the researchers conducted a second experiment. Participants were divided into two groups: one experienced the tour in the evening and slept overnight in a monitored sleep lab, while the other took the tour in the morning and remained awake until retesting in the evening. Memory was tested again after one week, one month, and 15 months.
The results reinforced the initial findings:
- A single night of sleep significantly improved memory for the sequence of events, an effect that lasted up to 15 months.
- Sleep had no impact on memory for visual features, which continued to fade over time.
- EEG recordings showed that slow waves and sleep spindles during deep sleep were strongly linked to memory enhancement.
“This study shows how deep sleep benefits memory for the sequential structure of everyday events, even when specific details fade,” said Dr. Levine. “The benefits of sleep on memory are powerful; just one night makes a difference that persists over a year.”
These findings offer new insights into how memory works and may help explain why people with dementia often struggle with the timeline of their memories. Understanding how sleep influences memory consolidation could open new doors in treating age-related memory decline.
The study was supported by funding from the Canadian Institutes of Health Research.
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