Sleep disturbance and depression are common, particularly in females, and sleep disturbance is a well-known risk factor for depression. Systemic inflammation has been suggested as a potential mechanism of this association. This study examined whether preexisting sleep disturbance acted as a vulnerability factor for depressed mood induced by an inflammatory challenge in healthy females vs males. In a randomized double-blind placebo-controlled design, volunteers aged 18-50 (N = 111; 67 females) were assigned to placebo or low-dose endotoxin. Before substance administration, sleep disturbance was assessed using the Pittsburgh Sleep Quality Index and dichotomized using median split (⩾ 3 vs < 3). Self-reported depressed mood (profile of mood states) and circulating proinflammatory cytokines (interleukin-6, tumor necrosis factor-α) were repeatedly assessed over 6 h. Among females, moderation of depressed mood by sleep disturbance was significant even after adjustment for covariates (X(2) = 12.73, df = 6, P < 0.05). There was a robust time-by-condition interaction in females with sleep disturbance (X(2) = 26.22, df = 6, P < 0.001), but not in females without sleep disturbance (X(2) = 8.65, df = 6, P = 0.19). Although cytokines increased equally in all females, the correlations between cytokines and depressed mood were significantly stronger in females with sleep disturbance. Among males, no moderating effect of sleep disturbance was observed. Inflammation-induced depressed mood was considerably more severe among females reporting mild sleep disturbance compared with those reporting no sleep disturbance, suggesting that even mild sleep disturbance may increase vulnerability for inflammation-induced depression in females. Furthermore, sleep disturbance appears to increase the vulnerability to depression by augmenting affective sensitivity to cytokines rather than by enhancing cytokine responses to inflammatory challenge in females.

Neuropsychiatric disorders (e.g., autism, schizophrenia) are partially characterized by social cognitive deficits, including impairments in the ability to perceive others' emotional states, which is an aspect of social cognition known as theory of mind (ToM). There is also evidence that inflammation may be implicated in the etiology of these disorders, but experimental data linking inflammation to deficits in social cognition is sparse. Thus, we examined whether exposure to an experimental inflammatory challenge led to changes in ToM. One hundred and fifteen (n = 115) healthy participants were randomly assigned to receive either endotoxin, which is an inflammatory challenge, or placebo. Participants completed a social cognition task, the Reading the Mind in the Eyes (RME) test, at baseline and at the peak of the inflammatory response for the endotoxin group. The RME test, a validated measure of ToM, evaluates how accurately participants can identify the emotional state of another person by looking only at their eyes. We found that endotoxin (vs. placebo) led to decreases in performance on the RME test from baseline to the peak of inflammatory response, indicating that acute inflammation can lead to decreases in the ability to accurately and reliably comprehend emotional information from others. Given that deficits in ToM are implicated in neuropsychiatric disorders, including those which may have an inflammatory basis, these results may have implications for understanding the links between inflammation, social cognition, and neuropsychiatric disorders. Clinical Trials Registration.

Psychological stress is implicated in the etiology of many common chronic diseases and mental health disorders. Recent research suggests that inflammation may be a key biological mediator linking stress and health. Nevertheless, the neurocognitive pathways underlying stress-related increases in inflammatory activity are largely unknown. The present study thus examined associations between neural and inflammatory responses to an acute laboratory-based social stressor. Healthy female participants (n = 31) were exposed to a brief episode of stress while they underwent an fMRI scan. Blood samples were taken before and after the stressor, and plasma was assayed for markers of inflammatory activity. Exposure to the stressor was associated with significant increases in feelings of social evaluation and rejection, and with increases in levels of inflammation. Analyses linking the neural and inflammatory data revealed that heightened neural activity in the amygdala in response to the stressor was associated with greater increases in inflammation. Functional connectivity analyses indicated that individuals who showed stronger coupling between the amygdala and the dorsomedial prefrontal cortex (DMPFC) also showed a heightened inflammatory response to the stressor. Interestingly, activity in a different set of neural regions was related to increases in feelings of social rejection. These data show that greater amygdala activity in response to a stressor, as well as tighter coupling between the amygdala and the DMPFC, are associated with greater increases in inflammatory activity. Results from this study begin to identify neural mechanisms that might link stress with increased risk for inflammation-related disorders such as cardiovascular disease and depression.