Understanding Altruistic Behavior: The Joint Role of Prefrontal Damage and OXTR Genotype

Trait altruism varies widely between individuals, and the evidence points to two contributing sources: variation in the oxytocin receptor (OXTR) gene, which regulates the emotions underlying altruistic attitudes such as empathy and trust, and top-down control by the prefrontal cortex (PFC), whose reported effects on prosocial behavior have been contradictory. The authors hypothesized that extensive prefrontal damage would amplify the influence of genotype on altruism, and tested this in 115 male combat veterans with penetrating traumatic brain injury and 35 demographically matched uninjured controls, all assessed with a self-report altruism questionnaire and genotyped for four OXTR polymorphisms. Individuals homozygous for the G allele of rs53576 and rs7632287 were significantly more altruistic than carriers of a risk allele, and among patients with prefrontal damage, greater lesion extent was associated with markedly lower altruism in rs7632287 A-allele carriers but not in G-homozygotes. This is the first account of an interaction between OXTR genotype and the location and extent of brain damage, suggesting that prefrontal reasoning normally obscures genetically encoded dispositions toward prosocial behavior.