The impact of sleep loss on emotion regulation and emotional perception in young adults

Abstract

Sleep and emotional wellbeing are closely related. There are increasing interests in examining the alteration of emotion-related processes after sleep deprivation as potential mechanisms underpinning the link between sleep disturbances and emotional psychopathology. This thesis explores the functioning of emotion regulation and emotional perception processes in individuals with sleep loss.

In Study 1, 51 young healthy adults were randomly assigned to a sleep control (SC, n=25) group or a sleep deprivation (SD, n=26) group. In the morning after sleep manipulation, all participants completed an emotion regulation task with electroencephalographic (EEG) recordings, in which they implemented a given emotion regulation strategy (distraction, reappraisal or suppression) towards unpleasant pictures. The event-related potential (ERP) data suggested that reappraisal in the SD group was significantly less effective in attenuating the centroparietal late positive potential (LPP) towards unpleasant pictures than the SC group. There was only a statistical trend to the diminishing influence of sleep deprivation on the attenuating effect of distraction on LPP amplitudes. Suppression was ineffective in attenuating the LPP towards unpleasant pictures in both groups. Findings in Study 1 suggest that sleep loss may generally diminish the effectiveness of adaptive emotion regulation strategies, particularly the strategy of reappraisal.

Study 2 investigated 8-minute resting-state EEG measures before the emotion regulation task in Study 1. The power ratio of theta and beta bands over the prefrontal region (frontal theta/beta ratio) and the difference in alpha band power between the right and left frontal hemispheres (frontal alpha asymmetry) were calculated to index the prefrontal cortical control over the subcortical emotional reactivity. Significantly higher frontal theta/beta ratio and marginally more left-lateralized alpha band were found the SD group compared with the SC group. The findings in Study 2 converged in suggesting poorer functioning of the emotional regulatory neural network in a resting state after sleep deprivation.

Study 3 examined the recognition of emotional facial expressions in individuals with insomnia symptoms. Young adults with insomnia symptoms (n=23, insomnia group) and age- and gender-matched non-insomnia controls (n=23, control group) completed a task of categorizing emotional facial expressions (happiness, sadness, fear, anger) with eye tracking. It was found that the insomnia group was less accurate in identifying angry facial expressions than the control group. In addition, most individuals with insomnia symptoms adopted a holistic eye movement pattern that only looked at areas along the vertical face midline. In contrast, most individuals in the control group adopted an analytic eye movement pattern that looked at more lateral features such as the two eyes and the mouth corners. The compromised recognition of angry faces in individuals with insomnia may be related to their eye movement patterns, which usually missed the eyes as an important diagnostic feature, suggesting a role of visual attention functioning in the relationship between sleep and emotional perception.

Overall, this thesis found compromised functioning of emotion regulation and emotional perception in individuals with sleep loss, which contributes to our understanding of the sleep-emotion link and generates implications for the emotional wellbeing in individuals with sleep problems.