Night-time sleep improves one's recall of sequence of events benefits seen even after a year Study

PTI, April 11, 2025, New Delhi: Night-time sleep improves one's recollection of the sequence of events, rather than simply protecting memory from declining, according to a study.

Findings of the study, published in the journal Nature Human Behaviour, also showed that the benefits of a night's sleep in remembering the order of events were evident even after more than a year.

"While our memory for features such as object size and colour declines over time, sleep can improve our memory for event sequence," said senior author Brian Levine, senior scientist at the Rotman Research Institute, Baycrest Academy for Research and Education, Canada.

"This study deepens our understanding of how critical sleep is for integrating experiences into memory," Levine added.

The researchers explained that the study involved a 20-minute audio-guided tour of artworks displayed at Baycrest. Over 50 participants took the tour and responded to questionnaires that tested their memory.

The tests were taken at five intervals, starting from an hour to 15 months after the tour, and included questions on the physical features of the artwork and the sequence of tour items.

The researchers found that sleep boosted the participants' recollection of the sequences, whereas memory of the features declined.

"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)," the authors wrote.

As part of a second experiment, the participants were randomly assigned to either a wake or a sleep group. Both groups did the tour and took two memory tests. However, the sleep group took the second memory test after a night of sleep in a sleep laboratory, while the wake group took it in the evening after normal daily activities.

Additional memory tests were completed by both groups one week, one month, and 15 months after the tour.

Recordings of brain activity showed that specific brain waves during deep sleep — slow waves and spindles — were linked to enhanced memory overall.

Further, advantages of sleep in recollecting the sequence of events were evident after a single night of sleep, and this advantage held at all test points, including 15 months later, the researchers said.

"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," the authors wrote.

"These results suggest that sleep serves a crucial and selective role in enhancing sequential organisation in our memory for past events," they concluded.