Sleep and emotional processing in adolescents and young adults

Abstract

Insufficient sleep is a common issue among adolescents and young adults and is often associated with altered emotional responses and an increased risk for mental health problems. In addition to short sleep duration, excessive daytime sleepiness (EDS) has been suggested to represent an individual’s unmet sleep need. However, there has been limited research to examine the interplay between sleep duration and EDS in relation to emotional processing. The present thesis conducted two studies: Study 1 was a cross-sectional study to examine the association of short sleep duration and EDS with emotional conflict regulation in adolescents and young adults. Study 2 was an experimental study to examine the effects of acute sleep deprivation and associated sleepiness on emotional facial expression recognition using eye tracking technique.

Study 1 involved 149 youths aged 13-24 years old who completed self-report questionnaires on sleep and mood, objective measure of sleep by actigraphy for seven consecutive days, and an emotional conflict task designed to assess one’s ability to stay focused on a task whilst not being distracted by irrelevant emotional stimuli. The results showed that participants with EDS (Pediatric Daytime Sleepiness Scale score > 15 for participants aged under 18, or Epworth Sleepiness Scale score > 9 for participants aged 18 and above) had larger differences in reaction time and accuracy between incongruent trials and congruent trials, as compared to their peers without EDS, indicating poorer regulation of emotional conflict (i.e. more easily distracted by irrelevant emotional stimuli). However, short sleep duration (< 7 hours of daily sleep as measured by actigraphy) was not found to be associated with emotional conflict control.

Study 2 adopted an experimental paradigm of sleep deprivation, in which 40 participants completed the facial expression recognition task under two conditions (sleep-rested vs. sleep-deprived). One night of acute sleep deprivation was not found to affect participants’ recognition of the emotions of facial expression (i.e. happy, sad, fearful, angry) after controlling for age, gender, habitual sleep duration and chronotype preference. In sleep-rested condition, subjective daytime sleepiness as measured by Stanford Sleepiness Scale was negatively associated with the accuracy of identifying angry faces. Greater changes in sleepiness (the difference in sleepiness between sleep-rested and sleep-deprived conditions) were associated with lower intensity of the rating of angry faces at a marginal significance. A Hidden Markov modeling analysis of the eye movement data revealed two distinct patterns when scanning emotional faces, with one focusing on both eyes and nose regions (“eyes-nose pattern”) whilst the other mainly attending to the nose region (“nose-mouth pattern”). Neither sleep deprivation nor daytime sleepiness was observed to affect participants’ eye movement patterns when scanning emotional faces.

In summary, excessive daytime sleepiness but not short sleep duration was associated with impaired emotional conflict regulation in adolescents and young adults. In addition, experimentally induced acute sleep deprivation did not impact on an individual’s emotional facial expression recognition and visual attention, whereas subjective daytime sleepiness in response to sleep deprivation was associated with altered perception of angry faces. Taken together, the findings of this thesis demonstrated subjective daytime sleepiness as an important factor associated with altered emotional processing. Future research is needed to further delineate the neural mechanisms underlying the association between daytime sleepiness and altered emotional processing.