Consummatory deficits in close social reward predict inflammation-induced depressed mood.

BACKGROUND: Inflammation is implicated in the etiology of depression, but not all individuals develop mood symptoms when exposed to inflammatory states. Identifying psychological predictors of this vulnerability is critical for advancing mechanistic models of depression. Deficits in global reward processing predict risk for depression, but reward processing involves both temporal dimensions (e.g., anticipatory vs. consummatory pleasure) and experiential domains (e.g., social vs. non-social). It remains unknown whether specific aspects of reward experience predict greater affective sensitivity to inflammation. This study examined whether lower in-the-moment and anticipated enjoyment across multiple reward domains in daily life predicted greater increases in depressed mood following an experimental inflammatory challenge. METHODS: Secondary analyses were completed on data from healthy female adults (n = 40; age 25-44) who were enrolled in a double-blind, randomized, placebo-controlled trial in which participants were randomly assigned to receive either low-dose endotoxin (n = 18) or placebo (n = 22) and reported on depressed mood pre- and post-infusion. Prior to the challenge, participants completed a 7-day ecological momentary assessment (EMA) protocol, rating anticipated and in-the-moment enjoyment five times daily across three reward domains: close social interactions, general social interactions, and non-social experiences. RESULTS: Linear mixed models were used to generate person-level estimates of EMA reward ratings. Endotoxin induced increases in depressed mood (p = .001), and this effect was moderated by enjoyment of close social interactions; lower enjoyment was associated with greater depressed mood responses to endotoxin (p = .004). Results were similar when adjusting for baseline levels of depressive symptoms. Enjoyment of general social interactions and non-social rewards, as well as anticipated enjoyment across all reward domains, did not moderate depressed mood responses to the inflammatory challenge (p's > .05). DISCUSSION: These preliminary results suggest that reduced enjoyment of close social interactions uniquely predicts vulnerability to inflammation-induced depressed mood in female adults. Interventions targeting close social relationships and strategies for savoring social experiences may play a critical role in preventing inflammation-related depression.