Laboratory-measured aggressive behavior of women: acute tryptophan depletion and augmentation

Plasma L-tryptophan (Trp) reductions have been related to aggression increases in men. Impairment of serotonin synthesis and neurotransmission is one explanation. Using repeated-measures, this Trp manipulation study measured laboratory-induced aggression in 12 women after Trp augmentation (T+), depletion (T-), and food-restricted (fasting control) conditions. Participants were provoked with periodic subtraction of money from their task earnings by a (fictitious) partner. Aggression was defined as the number of point subtractions participants made from their fictitious partner. Participants completed five testing sessions under each condition. T+ decreased aggressive responses and T- increased aggressive responses. Post-hoc analyses showed changes in aggressive behavior were specific to women with higher fasting control plasma Trp, which is consistent with research demonstrating that men with higher levels of baseline Trp are more aggressive. These findings indicate that both T+ and T- can influence aggressive behavior and that certain subgroups of women may be more susceptible to serotonin manipulation.