Brain alterations potentially associated with aggression and terrorism.

A large proportion of the persons who join terrorist groups as well as lone-acting terrorists have a history of violent behavior or mental disorder that predated their becoming terrorists. This suggests that brain alterations found to occur in violent perpetrators may also be present in a significant percentage of terrorists. After a short delineation of phylogenetically old neuronal networks that are important for the generation of aggressive behavior in inconspicuous brains, this review summarizes structural and functional brain-imaging studies in violent offenders published over the last 10 years. Depending on the subtype of violence (impulsive or instrumental), deviations in structure or function were mainly found in the prefrontal, orbitofrontal, and insular cortex, as well as in temporolimbic structures (e.g., the amygdala, hippocampus, and parahippocampus). These brain areas are essentially responsible for the control of the archaic neuronal generators of aggression located in the hypothalamus and limbic system. This regional distribution of brain alterations also shows a remarkable overlap with those brain regions that are crucial for such prosocial traits as empathy and compassion. Feelings of superiority, dominance, and satisfaction gained by performing violent and terroristic attacks suggest that a hedonistic component via an activation of brain reward systems plays an additional role. In our current debate about the causes of terrorism, aspects of brain dysfunction should receive more attention.