The effect of acute tryptophan depletion on emotional distraction and subsequent memory

Serotonin is a key neurotransmitter involved in emotional regulation and memory. A number of studies using acute tryptophan depletion (ATD) in healthy subjects have shown that a temporary serotonin reduction both induces a negative emotional bias and impairs long-term memory. However, little is known about the specific effects of ATD on emotional memory. Using functional magnetic resonance imaging (fMRI), we investigated the effect of ATD on negative memory and executive function in healthy volunteers. Our emotional oddball task required participants to distinguish infrequently presented targets from distracting negative and neutral pictures. Memory for the distracting pictures was tested 1 h following the fMRI session. ATD selectively enhanced memory for negative distractors relative to neutral distractors and increased activation in response to the negative distractors in the left orbital-inferior frontal, dorsomedial prefrontal and bilateral angular gyri. ATD also induced greater activation in the left inferior frontal gyrus and anterior cingulate across all stimuli. Stronger frontal activation to distractors was positively correlated with memory performance on ATD but not control days, indicating a possible compensatory mechanism for coping with increased task demand under the ATD challenge. These findings highlight the importance of serotonin in negative memory with implications for mood disorders.