In fact, there was no opponent. All of the participants were subjected to the noise—which kept getting louder—half of the time. As the volume increased, the women with depleted tryptophan aggressively cranked up the volume, lashing out at their imaginary opponent. The study concluded that lowering the precursor to serotonin in healthy women increases their tendency toward aggressiveness. “They were much more likely to retaliate than women with normal levels of serotonin,” says Alyson Bond, who conducted the study. “They behaved in a similar way to habitually aggressive people.”
