The following is a summary of “Effects of an experimentally induced inflammatory stimulus on motivational behavior in remitted depressed patients,” published in the May 2023 issue of Psychiatric Research by Suchting, et al.
Acute inflammation is associated with illness behavior in humans characterized by diminished motivation for enjoyable activities. This study examined the effect of an experimentally induced inflammatory stimulus on motivational reward in depressed individuals who had recovered.
Five participants with remitted major depressive disorder (rMDD) and seven healthy controls (HC) received intramuscular injections of typhoid vaccine and placebo (or vice versa) at least one week apart in this randomized, double-blind crossover study. At baseline and between 4 and 6h post-injection on both days, the mood was assessed using the profile of mood states (POMS), and blood samples were drawn for cytokine analysis.
Before and 4h post-both injections, all participants completed the Effort Expenditure for Rewards Task (EEfRT), a behavioral paradigm measuring effort-based decision-making. Generalized linear mixed modeling assessed group differences in selecting the difficult over the simple task for monetary compensation. The typhoid vaccine elevated IL-6 levels in all participants. On the EEfRT, a significant interaction was observed between the treatment condition (typhoid versus placebo) and the participant group (HC versus rMDD; P =.004). Analyses of simple effects within treatment conditions revealed that, following a placebo, HCs were more likely than rMDD to choose the more difficult task (OR = 3.21; P =.013). After receiving the typhoid vaccine, there were no differences between rMDD and HC (P =.397).
Analyses within participant groups revealed that the likelihood of selecting a difficult task was greater after a placebo for HC (OR = 1.37; P =.045) but not for rMDD (P=.241). For HC at baseline, the mood was significantly lower following typhoid vaccine injection compared to placebo (b = -1.03, P< .001); however, this effect should be regarded as coincidental, as a mood rating was taken before injection. For rMDD patients 4–6h post-injection, the typhoid vaccine significantly decreased mood compared to placebo (b = -0.981, P <.001; b = 0.77, P< .001). About 4–6h after the placebo injection, the mood of HC was significantly lower compared to baseline (b = -1.76, P< .001). Despite clinical improvement, the researchers’ preliminary findings indicate recurrent deficits in the processing of motivational rewards in remitted depressed patients.