Inflammation causes mood changes through alterations in subgenual cingulate activity and mesolimbic connectivity.
Level 2 - randomized trial
Individual double-blind randomized crossover trial
PubMed 19423079 · doi:10.1016/j.biopsych.2009.03.015
What was done
In a double-blind, randomized crossover study, 16 healthy male volunteers received a typhoid vaccination or saline (placebo) injection across two experimental sessions. Mood questionnaires were completed at baseline, 2 hours, and 3 hours post-injection. Two hours after injection, participants completed an implicit emotional face perception task during functional magnetic resonance imaging (fMRI) to evaluate neural activity and connectivity within affective processing regions.
What was found
Typhoid vaccination produced an inflammatory response indexed by increased circulating interleukin-6 (IL-6) and a significant reduction in mood at 3 hours compared to placebo. Inflammation-associated mood deterioration correlated with enhanced activity in the subgenual anterior cingulate cortex (sACC) during emotional face processing. Furthermore, this mood deterioration was associated with reduced functional connectivity between the sACC and the amygdala, medial prefrontal cortex, nucleus accumbens, and superior temporal sulcus, which was modulated by peripheral IL-6 levels. Exact numerical values and effect sizes were not reported in the abstract.
Why it matters
This study provides experimental human evidence demonstrating that peripheral inflammation can alter central mood-regulatory circuits, specifically sACC activity and mesolimbic connectivity. It supports a mechanistic neurobiological link between systemic inflammatory signaling and depressive symptoms.
Limits
The study had a very small sample size (n = 16) consisting exclusively of healthy male volunteers, limiting generalizability to females and clinical populations. The acute immune challenge model (typhoid vaccine) may not capture the chronic inflammatory states typically associated with major depressive disorder, and no long-term follow-up beyond 3 hours was evaluated.
Cited by
- supports Studies by Hugo Critchley's group showed that administering typhoid vaccine to healthy individuals induces acute dysphoria, increased feelings of social isolation, and changes in depressive brain circuitry.