The brain regulates social behavior differently in males and females, according to a new study. A team of researchers has discovered that serotonin (5-HT) and arginine-vasopressin (AVP) act in opposite ways in males and females to influence aggression and dominance. Because dominance and aggressiveness have been linked to stress resistance, these findings may influence the development of more effective gender-specific treatment strategies for stress-related neuropsychiatric disorders.