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To examine the linkage between inflammation, illness behavior, and depression, U.K. investigators conducted a two-session, crossover study using a reinforcement-learning task. Placebo or typhoid vaccine was administered in random order before each session. The 24 normal subjects (mean age, 28) learned to predict from previous exposure which stimuli were likely to signal reward (win money), punishment (lose money), or no value; 17 participants underwent functional magnetic resonance imaging during the sessions.
Typhoid vaccine induced a robust inflammatory response (i.e., increased interleukin 6 levels), without change in body temperature or physical symptoms other than fatigue. Although no changes occurred in the learning process or in the d…