Summary: Sleep strengthens both original and updated versions of memories, enabling flexible, adaptive use of past experiences, researchers report.
Source: University of York.
Researchers at the University of York have provided new evidence on how sleep supports memory flexibility and resilience.
The team found that sleep does more than simply consolidate a single memory trace. Instead, sleep appears to preserve multiple versions of the same experience—both the original memory and newer, updated variants formed when the memory is retrieved—allowing the brain to draw on different representations as circumstances demand.
Their findings, produced by the Sleep, Language and Memory (SLAM) Laboratory at York, are published in the journal Cortex.
Adapt memories
Lead researcher Dr Scott Cairney from the Department of Psychology explained that earlier studies have already established the importance of sleep for long-term memory. This study extends that work by showing that sleep strengthens not only the memory we originally encoded but also the modified version that can form when a memory is retrieved and updated.
“Sleep helps us use memory in the most efficient and adaptive way,” Dr Cairney said. “By strengthening both old and newly updated memory traces, sleep enables us to update our knowledge and to adapt how we remember events for future use.”
In the experiment, participants learned the screen locations of a set of words. During a first test (T1), each word was presented at the centre of the screen and participants indicated where they believed the word had been positioned. Some time later, after either a 90-minute nap or an equivalent period spent awake, participants completed the test again (T2).
Results showed that at T2 most words were recalled closer to the location participants had given at T1 than to the originally learned location, indicating that memory had been updated during retrieval. Crucially, comparison between the sleep and wake groups revealed a distinct pattern: after sleep, recalled locations at T2 were closer to both the T1-updated locations and the original study locations.
Protective effect
Professor M. Gareth Gaskell, corresponding author and member of York’s Department of Psychology, said the pattern indicates a protective effect of sleep. “Sleep strengthened participants’ memory for the original location as well as for the new, retrieved location,” he said. “This suggests that sleep preserves multiple representations of the same experience rather than overwriting one version with another.”
In other words, when retrieval produces an altered memory trace, sleep appears to consolidate that altered trace alongside the original, creating co-existing memory representations that can be used flexibly.
Distortion
The authors note an important caveat: while maintaining multiple memory variants supports adaptability, it also creates potential for distortion. If erroneous information is incorporated during retrieval, that distorted version can be preserved and later used alongside accurate versions, which may lead to biased or inaccurate recollections over time.
The study follows a research framework developed by Ken Paller, Professor of Psychology at Northwestern University and a co-author on this work, which examines how retrieval and sleep interact to shape long-term memory.
Funding: The research was funded by the Economic and Social Research Council (ESRC).
Source: Caron Lett, University of York.
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Original Research: “Sleep preserves original and distorted memory traces” by Scott A. Cairney, Shane Lindsay, Ken A. Paller, and M. Gareth Gaskell in Cortex. Published online October 16, 2017. doi:10.1016/j.cortex.2017.10.005
Abstract
Sleep preserves original and distorted memory traces
Retrieval can strengthen memories but can also update them with new information available at the time of recall. If that newly incorporated information is inaccurate, later recall may be impaired—a phenomenon known as retrieval-induced distortion (RID). It has been unclear whether RID overwrites original memory traces or creates additional, co-existing variants. Because sleep enhances consolidation, examining memory after sleep can reveal the structure of updated memories. In this study, participants encoded word locations and were tested before (T1) and after (T2) an interval of sleep or wakefulness. At T2 most words were recalled closer to their T1-retrieved locations than to their original studied locations, consistent with RID. After sleep, however, T2 responses were closer to both the studied and the T1-retrieved locations. These results suggest RID produces an additional distorted trace that co-exists with the original and is strengthened alongside it during sleep, highlighting sleep’s role in preserving and adaptively updating memories.
“Sleep preserves original and distorted memory traces” by Scott A. Cairney, Shane Lindsay, Ken A. Paller, and M. Gareth Gaskell in Cortex. Published online October 16, 2017. doi:10.1016/j.cortex.2017.10.005