Sleep, inflammation, and perception of sad facial emotion: A laboratory-based study in older adults

Background: Facial emotion perception (FEP) is pivotal for discriminating salient emotional information. Accumulating data indicate that FEP responses, particularly to sad emotional stimuli, are impaired in depression. This study tests whether sleep disturbance and inflammation, two risk factors for depression, contribute to impaired FEP to sad emotional stimuli. Methods: In older adults (n = 40, 71.7 ± 6.8y, 56.4% female), disturbance of sleep maintenance (i.e., wake time after sleep onset [WASO]) was evaluated by polysomnography. In the morning, plasma concentrations of two markers of systemic inflammation were evaluated (i.e., interleukin [IL]-6, tumor necrosis factor [TNF]-α), followed by two FEP tasks, which assessed delays in emotion recognition (ER) and ratings of perceived emotion intensity (EI) in response to sad facial emotional stimuli, with exploration of FEP responses to happiness and anger. Linear regression models tested whether WASO, IL-6, and TNF-α would be associated with impaired FEP to sad emotional stimuli. In addition, moderation tests examined whether inflammation would moderate the link between sleep disturbance and impaired FEP to sad emotional stimuli. Results: Longer WASO predicted longer ER delays (p < 0.05) and lower EI ratings in response to sad faces (p < 0.01). Further, higher TNF-α (p < 0.05) but not IL-6 predicted longer ER delays for sad faces, whereas higher IL-6 (p < 0.01) but not TNF-α predicted lower EI ratings for sad faces. Finally, TNF-α moderated the relationship between longer WASO and longer ER delays to sad faces (p < 0.001), while IL-6 moderated the relationship between longer WASO and lower EI ratings to sad faces (p < 0.01). Neither sleep nor inflammatory measures were associated with FEP responses to happiness or anger. Conclusion: In older adults, disturbance of sleep maintenance is associated with impaired FEP to sad emotion, a relationship that appears to be moderated by inflammation. These data indicate that sleep disturbance and inflammation converge and contribute to impaired FEP with implications for risk for late-life depression.