Recognizing emotions in faces: effects of acute tryptophan depletion and bright light.

In healthy never-depressed individuals, acute tryptophan depletion (ATD) may selectively decrease the accurate recognition of fearful facial expressions. Here we investigated the perception of facial emotions after ATD in more detail. We also investigated whether bright light, which can reverse ATD's mood-lowering effect, can also reverse its effect on the perception of facial emotions. On two separate test days, spent in a room that was either bright (n = 14) or dim (n = 16), healthy never-depressed women completed a facial emotion perception task six hours after ingesting tryptophan-deficient and balanced amino acid mixtures. Treatments were administered double blind and in randomized order using a crossover design. In dim light ATD decreased recognition accuracy of anger, disgust, and surprise. The labeling of fear and sadness was not affected. In bright light no effects of ATD were seen. Bright light was identified as a potential confounding factor in task performance. The effects of ATD on facial emotion perception may be less emotion-specific than thought previously, and occurred in a direction opposite to what might be expected based on theories of mood-congruent bias.