Narrator: This is Science Today. Serotonin is a neurotransmitter that many may know about due to low levels being associated with depression and anxiety. But a UCLA study has found that serotonin also affects our sense of fairness. Psychologist Matthew Lieberman, who led the study, explains.

Lieberman: We were using an experimental paradigm that allows us to look at how people react to fair and unfair treatment. There's a game that's called the Ultimatum Game, it's really less of a game and more of an economic bargaining device. Two individuals are given some amount of money to split between them.

Narrator: During the game, individuals who had depleted levels of serotonin were much more likely to reject what they considered to be unfair offers than those who had normal levels of serotonin. Lieberman says these findings provide insight into impulsive aggression.

Lieberman: When your serotonin levels are depleted, you may be more likely to see ambiguously unfair behaviors as truly unfair and therefore, reply in this much more aggressive manner.

Narrator: For Science Today, I'm Larissa Branin.