Background. Mood congruent memory bias predicts a more superior recall memory of learnt material congruent with the mood state at the time of learning. The present study is the first report of an experimental study in which a biological mood induction was used to test this hypothesis. The influence of acute tryptophan (TRP) depletion, inducing low serotonin neurotransmission and a depression of mood, on memory bias was evaluated in healthy volunteers (16 with and 11 without a family history of major affective disorder).

Methods. Twenty-seven subjects received 100 g of an amino acid mixture with and without TRP according to a placebo-controlled, double-blind, balanced, cross-over design. An affective memory test consisting of a 30-word list with words of positive, neutral, and negative affective valence and a mood questionnaire were assessed at 6 and 24 h following treatment administration.

Results. TRP depletion impaired delayed recall of neutral and positive words, but not of negative words. There was no interaction of family history and treatment and there was no post hoc association between the influence of TRP-depletion on mood and on affective memory bias.

Conclusion. Experimentally induced serotonergic depletion in normal individuals shifts affective memory bias towards negative affective valent verbal stimuli.