Acute tryptophan depletion attenuates conscious appraisal of social emotional signals in healthy female volunteers.
BACKGROUND
Acute tryptophan depletion (ATD) decreases levels of central serotonin. ATD thus enables the cognitive effects of serotonin to be studied, with implications for the understanding of psychiatric conditions, including depression.


OBJECTIVE
To determine the role of serotonin in conscious (explicit) and unconscious/incidental processing of emotional information.


METHODS
A randomized, double-blind, cross-over design was used with 15 healthy female participants. Subjective mood was recorded at baseline and after 4 h, when participants performed an explicit emotional face processing task, and a task eliciting unconscious processing of emotionally aversive and neutral images presented subliminally using backward masking.


RESULTS
ATD was associated with a robust reduction in plasma tryptophan at 4 h but had no effect on mood or autonomic physiology. ATD was associated with significantly lower attractiveness ratings for happy faces and attenuation of intensity/arousal ratings of angry faces. ATD also reduced overall reaction times on the unconscious perception task, but there was no interaction with emotional content of masked stimuli. ATD did not affect breakthrough perception (accuracy in identification) of masked images.


CONCLUSIONS
ATD attenuates the attractiveness of positive faces and the negative intensity of threatening faces, suggesting that serotonin contributes specifically to the appraisal of the social salience of both positive and negative salient social emotional cues. We found no evidence that serotonin affects unconscious processing of negative emotional stimuli. These novel findings implicate serotonin in conscious aspects of active social and behavioural engagement and extend knowledge regarding the effects of ATD on emotional perception.
Beacher
Felix D C C
FD
Clinical Imaging Sciences Centre, Brighton and Sussex Medical School (BSMS), Brighton & Hove, UK. f.beacher@bsms.ac.uk
Gray
Marcus A
MA
Minati
Ludovico
L
Whale
Richard
R
Harrison
Neil A
NA
Critchley
Hugo D
HD
D000328:Adult; D000339:Affect; D003071:Cognition / Q000502:physiology*; D018592:Cross-Over Studies; D003463:Cues; D004311:Double-Blind Method; D004644:Emotions; D005149:Facial Expression; D005260:Female; D006801:Humans; D011597:Psychomotor Performance; D011930:Reaction Time; D012701:Serotonin / Q000378:metabolism*; D014364:Tryptophan / Q000172:deficiency*; D055815:Young Adult
D012701:Serotonin; D014364:Tryptophan