Associations between sleep and cognitive-affective functioning in Posttraumatic Stress Disorder

Doctoral Thesis


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University of Cape Town

The current research tested the proposition that the sleep disruption characteristic of posttraumatic stress disorder (PTSD) has discrete, predictable, and significant effects on the processing of neutral declarative memory, emotional memory, and emotional reactivity. Research spanning multiple neuroscientific literatures demonstrates that healthy, uninterrupted sleep is critical for memory consolidation and emotional regulation, and that PTSD-diagnosed individuals experience sleep disruption, memory deficits, and emotional dysregulation. To test whether these behavioral, cognitive, and affective characteristics of PTSD are meaningfully related, I recruited three groups of participants: PTSD (n = 21), trauma-exposed non-PTSD (TE; n = 19), and healthy controls (HC; n = 20). Each participant was assessed before and after an 8-hour period of sleep and an 8-hour period of waking activity. The assessment featured measures of neutral declarative memory (learning of stimuli before the delay, and a free recall task afterward), emotional memory (exposure to highly-arousing negatively valenced, highly-arousing positively valenced, and low arousing neutral pictures before the delay, and a recognition task afterward), and emotional reactivity (physiological responses to the emotional pictures, both before and after the delay). The results are presented under the headings of four investigations. Investigation 1, which focused on objective and subjective sleep quality, suggested that PTSD-diagnosed participants had decreased sleep depth in comparison to HC participants, but presented with no other evidence of objective sleep disruption. Furthermore, PTSD-diagnosed participants reported better subjective sleep quality in the sleep laboratory than in their home environment, an effect not observed in TE and HC participants. Investigation 2, which focused on neutral declarative memory, suggested that after a sleep-filled, but not wake-filled, delay, PTSD-diagnosed participants retained less neutral declarative information than TE and HC participants. Furthermore, increased fragmentation of rapid eye movement (REM) sleep in PTSD-diagnosed individuals was a significant predictor of post-sleep memory retention deficits. In contrast, Investigations 3 and 4 suggested no significant between-group differences in emotional memory or emotional reactivity. However, Investigation 3 suggested that, after a sleep-filled delay, pictures of all valence and arousal categories were recognized equally accurately by all participants. In contrast, after a wake-filled delay all participants had higher recognition accuracy for negative pictures. Furthermore, Investigation 4 suggested that a sleep-filled delay attenuated emotional reactivity to pictures of all arousal and valence categories, whereas a wake-filled delay was associated with a rise in emotional reactivity across the day. Together, these results suggest that fairly small sleep disruptions (specific to REM-related changes) in PTSD-diagnosed individuals will affect retention of neutral declarative information, but will have no significant effects on the processing of, or reactivity toward, arousing and valenced stimuli. Overall, these findings allow the conclusion that, in PTSD, the co-occurrence of sleep and neutral declarative memory difficulties is not accidental – that is, these two symptom clusters are meaningfully related. Furthermore, the results demonstrate that a reasonable, not necessarily perfect, night of sleep in PTSD is associated with intact functioning within certain cognitive and affective domains. The research bolsters the neuroscientific view of sleep as a critical biological process linked integrally to psychological well-being.