Hemispheric processing of memory is affected by sleep

Abstract

Sleep is known to affect learning and memory, but the extent to which it influences behavioural processing in the left and right hemispheres of the brain is as yet unknown. We tested two hypotheses about lateralised effects of sleep on recognition memory for words: whether sleep reactivated recent experiences of words promoting access to the long-term store in the left hemisphere (LH), and whether sleep enhanced spreading activation differentially in semantic networks in the hemispheres. In Experiment 1, participants viewed lists of semantically related words, then slept or stayed awake for 12h before being tested on seen, unseen but related, or unrelated words presented to the left or the right hemisphere. Sleep was found to promote word recognition in the LH, and to spread activation equally within semantic networks in both hemispheres. Experiment 2 ensured that the results were not due to time of day effects influencing cognitive performance.

Lateralised sleep spindles relate to false memory generation

“…Lateralising stimuli to the RH may highlight false memory effects, but naps rather than overnight sleep may also increase false memory effects (Chatburn et al, 2014). Indeed, the results of our study, and that of previous studies of lateralisation of DRM stimuli (Bellamy & Shillcock, 2007;Ito, 2001;Monaghan et al, 2017;Westerberg & Marsolek, 2003) are consistent with the possibility that false memories may be generated in the RH. Dominance of false memory generation in the RH would be consistent with the two principal theories for sleep-induced processing changes associated with false memories -the gist theory (Brainerd & Reyna, 2005;Durrant & Lewis, 2009;Fischer et al, 2006;Gomez et al, 2006;Lutz et al, 2017;Wagner, Gais, Halder, Verieger, & Born, 2004) and the increased spreading activation theory (Cai et al, 2009;Monaghan et al, 2013).…”

“…For the first objective of the sleep false memory behavioural effects, we found that unseen-lure words were more likely to be falsely recognised after a nap, than after a period of wake, consistent with the literature of sleep increasing false memories compared to an equivalent period of wake Monaghan et al, 2017;Pardilla-Delgado & Payne, 2017;Payne et al, 2009). The subsequent signal detection analyses demonstrated that the enhanced false memories were not only due to changes in response bias, but were effects of sleep on discriminability between unseen lure and unseen new words.…”

“…Within the current study we had two main objectives. First, we aimed to replicate previous effects of sleep increasing false memory effects for words Pardilla-Delgado & Payne, 2017;Payne et al, 2009), as well as the interaction of these false memory sleep effects with hemispheric processing (Monaghan et al, 2017), who observed a hemispheric asymmetry after overnight sleep for recognition accuracy in the DRM paradigm. Second, we tested the relation between sleep architecture and false memory, not only for sleep stages but also for sleep spindles.…”

“…Criteria for including participants for analysis were participants reporting more than 6 hours sleep per night in the 3 nights leading up to the study and sleeping in the study for more than 50 minutes within the sleep condition, and all participants passed these criteria. We first tested whether previously observed behavioural effects of overnight sleep on memory for words were reproduced here in a nap study, determining (1) whether there was an overall false memory effect, i.e., greater unseen-lure word than unseen-new word acceptance; (2) whether this false memory effect was enhanced by sleep (Payne et al, 2009); and (3) whether the dominance of veridical memory of studied words in the LH was a consequence of sleep (Monaghan et al, 2017). We conducted a 3-way mixed ANOVA with response accuracy in terms of proportion of words recognised as old as the dependent variable, group (sleep or wake) as between subjects factor, and hemisphere (LH, RH) and word type (unseen-lure, unseen-new, seen-old) as within subjects factors.…”

“…In the current study we extended the behavioural study of Monaghan et al (2017), which demonstrated a lateralised effect of memory retrieval for DRM word lists, by using a nap study paradigm where we measured the relationship between sleep architecture and construction of false memories. We hypothesised that the key effects of sleep-enhanced false memory would be reproduced in our study.…”