Melbourne School of Psychological Sciences - Theses

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Author: Schenker, Maya Thalia × Type: PhD thesis × Subject: actigraphy × Subject: sleep ×

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    Sleep and PTSD: bi-directional relationship and underlying mechanism
    Schenker, Maya Thalia ( 2023-04)
    Post-traumatic stress disorder (PTSD) is a debilitating and enduring disorder that a small but significant number of people develop following exposure to a traumatic event. A common feature of PTSD is disrupted sleep including insomnia and nightmares. Ongoing difficulties in sleeping prevent the sleep-dependent adaptive processing of traumatic memories. Further, sleep disruptions prevent recovery, and perpetuate the disorder when established. This thesis aimed to investigate the bi-directional association between changes in sleep and PTSD symptoms as well as between sleep and underlying fear memory processes. In part I, I examined the immediate effect of changes in sleep on fluctuations of PTSD symptoms and vice versa. Here I used both subjective and, for the first time, objective measures of sleep (study 1). This study found differences in the association between sleep and daytime PTSD symptoms depending on the sleep measurement method. Additionally, preliminary evidence suggests sex-specificity in the association between night-time sleep and daytime PTSD symptoms. Part II focused on the role of sleep in fear conditioning and extinction learning – the experimental model of PTSD development and treatment. Extinction learning and extinction recall (i.e., the ability to learn and remember that previously dangerous stimuli are not threatening anymore) are thought to be impaired in PTSD and impacted by sleep. Particularly rapid eye movement (REM) sleep has been suggested as the sleep stage most important for processing emotional memories. First, a systematic review summarized the available literature assessing the effect of REM and other sleep stages using a meta-analytic approach (study 2). The overwhelming majority of research highlighted the importance of REM sleep, but the meta-analysis did not find the expected REM sleep effect on extinction recall. Following this and the finding from part I, the third and last study investigated the effect of subjectively reported sleep on fear conditioning and extinction learning (study 3). Again, no effect of subjective sleep indices on extinction recall was found. However, both studies found that there were differences between sexes and outcomes were dependent on the diagnostic status (study 2) or rather PTSD severity (study 3). Together, this thesis filled important gaps in the literature and highlighted that sleep is important in the expression of PTSD symptoms in day-to-day life as well as in the mechanism underling PTSD such as fear conditioning and extinction learning. However, the effect of sleep may vary depending on key associated factors. Specifically, the relationship may differ depending on the sleep measurement method (objective and subjective), the samples studied (clinical and control populations) and sex (men and women).