Turkey, cooperation and serotonin

Tryptophan is a chemical precursor to serotonin that can be found in turkey. A recent study suggest that it could reduce cooperation in prisoner's dilemma:

half of the volunteers were given a drink that depleted their tryptophan levels prior to the start of the game, thereby decreasing serotonin levels in their brain. Rogers and his team found that dampening serotonin activity significantly decreased the level of cooperation among the players, and that this group also rated fellow players as less trustworthy. "The findings suggest that a serotonin deficit might impair sustained cooperation," says Rogers.[technologyreview]