While sleep loss is shown to have widespread effects on cognitive processes, little is known about the impact of sleep loss on emotion processes. In order to expand on previous behavioral and physiological findings on how sleep loss influences emotion processing, we administered positive, negative, and neutral affective visual stimuli to individuals after one night of sleep deprivation while simultaneously acquiring EEG event related potential (ERP) data and recording affective behavioral responses. We compared these responses to a baseline testing session. We specifically looked at the late positive potential (LPP) component of the visual ERP as an established sensitive measure of attention to emotionally-charged visual stimuli. Our results show that after sleep deprivation, the LPP no longer discriminates between emotional and non-emotional pictures; after sleep deprivation the LPP amplitude was of similar amplitude for neutral, positive, and negative pictures. This effect was driven by an increase in the LPP to neutral pictures. Our behavioral measures show that, relative to baseline testing, emotional pictures are rated as less emotional following sleep deprivation with a concomitant reduction in emotional picture-induced anxiety. We did not observe any change in cortisol concentrations after sleep deprivation before or after emotional picture exposure, suggesting that the observed changes in emotion processing are independent of potential stress effects of sleep deprivation. Combined, our findings suggest that sleep loss interferes with proper allocation of attention resources during an emotional task.
Sleep loss has been shown to impact various aspects of cognitive processes (Killgore, 2010, Lim and Dinges, 2008 and McCoy and Strecker, 2011). However, compared to the clear impairments in attention that have been shown after sleep loss, sleep loss has been found to have mixed results on emotion processing. In particular, some studies have shown decreased emotionality after sleep loss indicated by blunted affect (Talbot, McGlinchey, Kaplan, Dahl, & Harvey, 2010), impaired accurate recognition of human emotions (Van der Helm, Gujar, & Walker, 2010), decreased emotional expressiveness (Minkel, Htaik, Banks, & Dinges, 2011), and reduced emotional intelligence (Killgore et al., 2008). However, other studies have found increased emotionality after sleep loss indicated by exaggerated responses to negative stimuli (Tempesta et al., 2010), increased amygdala activity in response to emotionally negative stimuli (Yoo, Gujar, Hu, Jolesz, & Walker, 2007), and increased reward network activity in response to emotionally positive stimuli (Gujar, Yoo, Hu, & Walker, 2011). These differences may be due to dissimilar testing methodologies between studies (e.g. different types of self-report assessments of sleepiness and emotion, hemodynamic brain responses). An alternative explanation here is that the changes in emotion that occur after sleep loss are due to impairments in attention (Chuah et al., 2010, Sterpenich et al., 2009 and Yoo et al., 2007). In other words, changes in tonic alertness due to sleep loss can impact emotion processing because emotional stimuli lose their ability to capture attention resources. Thus, in spite of an increase in amygdala activation after sleep deprivation, a decrease in attention to emotional stimuli would still result in a decrease in emotion processing and reactivity. In support of this theory, the increased amygdala activity seen after sleep loss is also associated with a decrease in amygdala-PFC functional connectivity, suggesting a reduction in emotion control processes after sleep deprivation (Yoo et al., 2007).
