Selective processing of social threat cues following acute tryptophan depletion

The aim of the present study was to investigate the effects of low dose tryptophan depletion on recovered depressed patients both on and off antidepressant medication on an emotional Stroop task using social threat cues. Twenty-four healthy volunteers, 24 euthymic volunteers with a history of depression not currently on antidepressant medication and 24 euthymic volunteers with a history of depression and currently on antidepressant medication were randomly allocated to double-blind treatment with either a tryptophan depleting or a balanced mixture. All participants then completed subjective mood ratings and an emotional Stroop task using social threat cues. The recovered depressed group on medication demonstrated an increase in selective processing of social threat cues on the emotional Stroop task in the tryptophan depletion compared to the control condition. This was not the case for either healthy controls or the recovered depressed group not on medication. Although none of the patients showed a clinically significant relapse following tryptophan depletion, the medicated group showed a small but statistically significant increase in self-rated depression on the Profile of Mood States (POMS). Our data indicate that low-dose acute tryptophan depletion elicits both cognitive processing typical of the depressed state and subtle changes in subjective mood in the recovered depressed group on medication, but not in the recovered depressed group not on medication. This suggests that these two groups may differ in their underlying vulnerability to compromised serotonin function.