• The interaction of sleep and hormones on emotion functioning

      Lustig, Kari; Department of Psychology
      Insufficient sleep has been associated with deficits in emotion processing; sleepy individuals show increased emotional reactivity and decreased emotion regulation. Individual differences that predict performance after sleep loss has remained largely elusive. Concentrations of cortisol, progesterone, and testosterone are candidate predictors for variability in performance following sleep loss. These hormones are associated with emotion functioning under well-rested conditions and show interactions with sleep and circadian rhythms. The central aim of this dissertation was to investigate the interaction of natural sleep and hormones on measures of emotion functioning. Study 1 examined the role of cortisol in the relationship between sleep (across the first three years of university), and self reported emotion functioning in undergraduate students. Poor sleep was associated with worse emotion regulation and reactivity, and greater concentrations of cortisol and cortisol/DHEA-S. Consistently poor sleepers over three years, who had high cortisol, experienced the greatest difficulties with emotion regulation. Study 2 investigated the association between sleep satisfaction and objective measures of sleep on self-reported emotional functioning in a group of children and adolescents. Importantly, in girls who were dissatisfied sleepers, being further though puberty was associated with the greatest difficulties with emotion regulation. Study 3 examined natural sleep, hormones, and menstrual phase on processing emotional stimuli. Participants completed sleep diaries and wore actigraphy watches for 3-weeks and completed measures of emotion perception on two occasions in the laboratory, in different menstrual phases for women. The study supported dynamic relationships between hormone concentrations and various measures of sleep duration and quality on the processing of emotion stimuli. Many relationships emerged for threatening emotions, indicating that high concentrations of testosterone, progesterone or cortisol, combined with poor sleep resulted in increased sensitivity towards threat detection. Together these studies provide evidence that hormones are an important factor in understanding the link between poor sleep and emotion functioning. Hormone concentration plays a role in understanding individual differences in response to sleep loss and can compound with sleep loss to result in worse emotional outcomes. Consideration of hormonal factors may help identify certain at-risk populations for sleep related deficits or timing of interventions.
    • Testing a Hypothesis of Non-REM Sleep Reinforcement and REM Sleep Refinement for the Benefits of Post-Learning Sleep on Memory Retrieval

      MacDonald, Kevin John; Department of Psychology
      It is well established that post-learning sleep benefits later memory retrieval, but there is still much to learn about the processes involved and the nature of these benefits. Sleep is composed of stages of non-REM (NREM) and REM sleep: NREM sleep, especially slow wave activity of NREM sleep, and REM sleep have been implicated in memory performance benefits, but the specific contributions of each state remain unclear. This thesis presents a hypothesis proposing that post-learning NREM sleep supports memory accessibility, benefitting the likelihood of successful memory retrieval, and that post-learning REM sleep supports memory fidelity, allowing for more accurate retrieval when retrieval is successful. This hypothesis was tested over studies examining the effects of an afternoon nap (Chapter 2), targeted memory reactivation during NREM slow wave sleep (Chapter 3), and both targeted memory reactivation during NREM slow wave sleep and selective deprivation of REM sleep (Chapter 4) on measures of memory accessibility and memory fidelity in visuospatial memory tasks. In each study, measures of sleep architecture and electroencephalographic power in sleep were examined as predictors of memory performance. Several identified associations and interactions further inform an understanding of how NREM sleep and REM sleep may benefit memory performance. Most notably, these studies consistently found greater slow wave activity of NREM sleep to be specifically associated with better maintenance of memory accessibility. These studies did not identify a clear effect of REM sleep. It is hoped that the hypothesis and findings presented stimulate additional inquires that will further our understanding of the individual and combined contributions of NREM and REM sleep.