Background Although inflammatory activity is known to play a role in depression, no work has examined whether experimentally induced systemic inflammation alters neural activity that is associated with anhedonia, a key diagnostic symptom of depression. To investigate this, we examined the effect of an experimental inflammatory challenge on the neural correlates of anhedonia—namely, reduced ventral striatum (VS) activity to reward cues. We also examined whether this altered neural activity related to inflammatory-induced increases in depressed mood. Methods Participants (n = 39) were randomly assigned to receive either placebo or low-dose endotoxin, which increases proinflammatory cytokine levels in a safe manner. Cytokine levels were repeatedly assessed through hourly blood draws; self-reported and observer-rated depressed mood were assessed regularly as well. Two hours after drug administration, neural activity was recorded as participants completed a task in which they anticipated monetary rewards. Results Results demonstrated that subjects exposed to endotoxin, compared with placebo, showed greater increases in self-reported and observer-rated depressed mood over time, as well as significant reductions in VS activity to monetary reward cues. Moreover, the relationship between exposure to inflammatory challenge and increases in observer-rated depressed mood was mediated by between-group differences in VS activity to anticipated reward. Conclusions The data reported here show, for the first time, that inflammation alters reward-related neural responding in humans and that these reward-related neural responses mediate the effects of inflammation on depressed mood. As such, these findings have implications for understanding risk of depression in persons with underlying inflammation.

Although research has established links between feelings of social isolation and inflammation, the direction of these effects is unclear. Based on the role that proinflammatory cytokines play in initiating “sickness behavior,” which includes symptoms such as social withdrawal, it is possible that inflammatory processes heighten feelings of ‘social disconnection.’ Here, we examined whether exposure to an inflammatory challenge increased self-reported feelings of social disconnection. In addition, because both inflammatory processes and feelings of social disconnection contribute to depressive symptoms, we also explored whether increases in feelings of social disconnection played a role in the link between inflammation and depressed mood. Participants were randomly assigned to either receive endotoxin, an inflammatory challenge, or placebo. Proinflammatory cytokines (IL-6, TNF-α) were collected at baseline and then hourly for six hours. Participants completed self-reports of sickness symptoms (“fatigue”), social disconnection (“I feel disconnected from others”), and depressed mood (“unhappy”) hourly. Results revealed that endotoxin led to significant increases (from baseline) in IL-6 and TNF-α levels as well as feelings of social disconnection and depressed mood. Moreover, controlling for increases in social disconnection eliminated the relationship between exposure to inflammatory challenge and depressed mood. This study demonstrates that inflammation can have social psychological consequences, which may play a role in cytokine-related depressive symptoms.

Although research has demonstrated a relationship between proinflammatory cytokine activity and depressive symptoms, the neurocognitive processes underlying this relationship have remained largely unexplored. Here, we examined the effect of proinflammatory cytokine activation on the neural correlates of socially painful experience and associated depressed mood. Participants received either low-dose endotoxin or placebo through intravenous injection. Levels of the proinflammatory cytokine, IL-6, were repeatedly assessed through hourly blood draws; self-reported depressed mood was assessed hourly as well. Two hours post-injection, participants completed a neuroimaging session in which they were socially excluded during an online ball-tossing game. Replicating previous research, individuals exposed to endotoxin, compared to placebo, showed increases in IL-6 levels and depressed mood. Although there were no meaningful differences between the endotoxin and control groups in neural responses to social exclusion, there were sex differences in the relationships between IL-6 increases and neural responses to exclusion among subjects exposed to endotoxin. Among females, but not males, exposed to endotoxin, increases in IL-6 were associated with increases in social pain-related neural activity (dorsal anterior cingulate cortex, anterior insula) that mediated the relationship between IL-6 increases and depressed mood increases. Implications of these sex differences in the neural correlates of cytokine-associated depressed mood and social pain are discussed.

These findings indicate that anxiety symptom clusters are differentially associated with specific sleep-related disturbances, underscoring the complex relationship of late-life anxiety to sleep. Results suggest that personalized treatments, such as targeted sleep interventions, may improve specific anxiety-symptom domains, or vice versa.

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While investigations have sought to identify the distinct and shared contributions of anxiety and depression to neurocognitive processes in late life, less is known regarding the further contribution of worry, a unique and critical dimension of affective dysregulation. Capturing the full range of symptoms, as inspired by the NIH Research Domain Criteria (RDoC), may provide finer-grained information on inter-relationships among worry, anxiety and depression on neurocognitive processing in later life. The objective of this study was to determine if the dimensional trait of worry intensifies known negative associations of dimensional measures of anxiety and depressive symptoms with neurocognitive processes, specifically cognitive control and memory processes. Using a cross-sectional and observational design, this study was conducted within a translational research center located with a Veterans medical center in Northern California. One hundred and nineteen community-residing older adults ages 65–91 years participated, and were characterized with psychiatric and neurocognitive dimensional measures. Affective symptom severity was assessed with the Penn State Worry Questionnaire, the Beck Anxiety Inventory (BAI), and the Beck Depression Inventory-II. Primary neurocognitive outcomes were inhibitory control assessed using a Stroop paradigm and delayed verbal memory assessed with the Rey Auditory Verbal Learning Test. Secondary outcomes included other less frequently examined cognitive control mechanisms (working memory, information processing, and verbal fluency) and memory processes (visual delayed memory). Contrary to prediction, the dimensional trait of worry attenuated negative associations between anxiety and depressive symptoms and inhibitory control on the one hand, and between depressive symptoms and delayed verbal memory processes on the other. In the secondary models, symptom dimensions were not associated with other cognitive control or visual delayed memory processes. Our fine-grained approach, in line with the NIMH RDoC model, suggests the neurocognitive processes associated with dimensional measures of late-life affective symptoms are dissociable. Specifically, dimensional measures of worry operate independently from other anxiety and depression symptoms to reveal differential patterns of neurocognitive processes associated with affective dysregulation.

Following a worry induction, older and younger adults endorsed a wide variety of negative affect beyond the typical emotions associated with worry. Greater sadness experienced by older compared with younger adults highlights the importance of considering negative affect states, particularly depression, when working with older adult worriers.

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