False Memories – Can Sleep Increase Them?by Sara Adaes, PhD | June 7, 2014
There are numerous reports on how important sleep is for memory consolidation. Sleep is known to benefit long-term memory storage, whereas sleep deprivation can significantly affect the retrieval of stored memories. The idea that sleep loss may promote false memory formation is quite intuitive and has been demonstrated in several studies. However, there is some evidence suggesting that sleep may also actively promote false memory formation.
A commonly used procedure for the study of false memories is the Deese–Roediger–McDermott (DRM) paradigm. In the procedure, participants are presented with a list of related words that are strongly associated to a keyword, known as the ‘lure’, which is deliberately not presented. For example, if the lure is “sleep”, the words that will be presented may be “bed”, “rest”, “nap”, “dream”, “pillow” and so on. The participants are then required to remember as many words from the list as possible. Typically, the omitted keyword is recalled with the same frequency as some of the words presented in the list. Participants tend to report that they remember hearing the lure word, thereby indicating a false memory that originated due to a semantic association with words that were indeed presented.
Numerous studies have applied the DRM paradigm to test the effect of sleep on the formation of false memories, but the findings are controversial. On one hand, there is evidence that sleep reduces false memory formation.
In a study evaluating the effect of sleeping immediately after learning, participants were asked to either sleep or stay awake after being given the list of semantically associated words. In a separate experiment from the same work, participants were either sleep deprived or not at retrieval. It was shown that sleep deprivation at memory retrieval enhanced false memories of the omitted words, as could be expected. However, sleep following learning did not increase the formation of false memories. A different study even showed that false recollection of omitted words was in fact reduced after sleep, relative to an equal time of wakefulness, with no change in correct recognition of presented words. These studies therefore indicated that sleep promotes a reduction of false memory formation.
But on the other hand, there is increasing evidence suggesting that sleep may actually promote false memory formation. Similar research on whether sleep after learning and sleep deprivation at retrieval enhance the generation of false memories reached different conclusions from those described above. Recall was tested following a night of sleep, a night of wakefulness (sleep deprivation) or daytime wakefulness. Compared with memory performance after daytime wakefulness, both nocturnal sleep and sleep deprivation at memory retrieval significantly enhanced false memories of omitted words. However, these effects were only observed in subjects with low general memory performance. But another study that also reported that a night of sleep increases both true and false recall in the DRM paradigm, compared to an equivalent period of daytime wakefulness, showed that false memories are indeed preferentially preserved by sleep.
How the emotional content of the words presented modulates the effect of sleep in false memory formation has also been evaluated. Participants were given lists of words that were either only neutral or only emotionally negative. Recall was tested after 12 hours of sleep or wakefulness. Participants who had slept recalled more presented words than those that stayed awake, reinforcing the effect of sleep in true memory consolidation. Interestingly, this effect was observed only for emotionally neutral lists; emotionally negative lists were not recalled as effectively. It was also shown that sleep did increase false memories but these were independent of the emotional content of the words.
Overall, it seems that under certain circumstances sleep can indeed promote false memories over true ones. But maybe it’s all about sleep promoting memory consolidation, regardless of its veracity.
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Berndt C, Diekelmann S, Alexander N, Pustal A, & Kirschbaum C (2014). Sleep fragmentation and false memories during pregnancy and motherhood. Behavioural brain research, 266, 52-7 PMID: 24589545
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Roediger, H., & McDermott, K. (1995). Creating false memories: Remembering words not presented in lists. Journal of Experimental Psychology: Learning, Memory, and Cognition, 21 (4), 803-814 DOI: 10.1037//0278-73126.96.36.1993
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