An fMRI study of cytokine-induced depressed mood and social pain: the role of sex differences.
Level 2 - randomized trial
Individual randomized controlled trial evaluating endotoxin versus placebo.
PubMed 19376240 · doi:10.1016/j.neuroimage.2009.04.040
What was done
Participants were randomized to receive an intravenous injection of either low-dose endotoxin or placebo. Blood levels of interleukin-6 (IL-6) and self-reported depressed mood were measured hourly. Two hours post-injection, participants underwent functional magnetic resonance imaging (fMRI) while experiencing social exclusion during an online ball-tossing task.
What was found
Endotoxin increased IL-6 levels and depressed mood compared to placebo (no quantitative figures or statistical values provided in the abstract). There were no direct group-level differences between endotoxin and placebo in overall neural responses to exclusion. However, among endotoxin-exposed participants, a sex difference emerged: in females only, IL-6 increases correlated with greater activity in social pain-related regions (dorsal anterior cingulate cortex and anterior insula), which mediated the relationship between rising IL-6 and increased depressed mood. This relationship was absent in males.
Why it matters
These findings suggest a potential sex-specific neural mechanism linking systemic inflammatory responses to depressive symptoms through heightened sensitivity to social rejection.
Limits
The abstract does not report the sample size, participant demographics, baseline health status, or numerical effect sizes. The laboratory model of acute endotoxemia and virtual social exclusion may not fully reflect chronic clinical depression or naturalistic social stress.
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