title: The role of sleep in memory consolidation
title: effects of lateralisation and emotion
titleType: Subtitle
Creators: name: Newbury, Chloe
Publisher: name: Lancaster University
Year: 2019

description: Sleep benefits both learning and memory, with offline memory consolidation
      leading to the reactivation and integration of new information into the
      long-term store. Previous literature further demonstrates an influence of
      sleep on memory for related but unseen information, termed false memories.
      However, current findings provide mixed results regarding sleep’s role in
      the formation of these false memories within the Deese-Roediger-McDermott
      (DRM) paradigm, with differing memory effects suggested to be due to
      various task differences. For word recognition, the reactivation of
      memories during sleep promotes access to the long-term store in the left
      hemisphere, whereas false memories may lead to equal spread of activation
      across the two hemispheres. Whether hemispheric processing of memories
      after sleep affects memories lateralised at encoding, rather than at
      retrieval, is however unknown. The emotionality of to-be-remembered
      information also enhances the consolidation effect, with greater veridical
      memory performance for both negative and positive stimuli. However, the
      effect of sleep on false memories varying in emotionality is yet unknown.
      This thesis therefore presents a series of experiments that examine
      several factors, namely lateralisation and emotionality, that may
      influence the role of sleep in learning and memory consolidation.
      
      In Chapter 2, we conduct a meta-analysis to establish the influence of
      sleep on veridical and false memories within the DRM paradigm literature.
      Although results suggest no overall effect of sleep, whether participants
      took part in a recall or recognition task, and the number of words within
      a DRM word list, moderated the effect. The role of sleep in DRM memory
      consolidation is therefore dependent on specific task features.
      
      Chapter 3 exposes participants to DRM word lists to the left or right
      hemisphere at encoding. The results demonstrate no hemispheric difference
      in memory performance after sleep for either veridical or false memories,
      suggesting that lateralisation effects after sleep are specific to
      retrieval processes.
      
      In Chapters 4 and 5, we use behavioural testing (Chapter 4) and
      polysomnography (PSG; Chapter 5) to investigate sleep-dependent veridical
      and false memory for emotionally negative, positive, and neutral DRM word
      lists. Findings demonstrate that negative emotion, compared to neutral,
      enhances veridical memory performance after sleep, whereas wake supports
      positive memory. Interestingly, sleep spindles during slow wave sleep
      (SWS) were found to correlate with increased memory performance for
      emotional words. In Chapter 6, we investigate the effect of sleep on
      learning of and memory for novel metaphorical word pairs of either
      negative, positive, or neutral valence. Findings demonstrate increased
      memory for emotional word pairs after sleep than wake.
      
      These results help clarify the role sleep plays in the formation of
      emotional memories, and highlights factors that modulate the effect of
      sleep on both veridical and false memories. We provide evidence that
      lateralisation effects are specific to retrieval processes, and suggest
      that sleep boosts the consolidation of emotional information, indicating a
      potential role of sleep spindles specific to SWS in the consolidation of
      emotional memories.