Brain lesions in previously law-abiding citizens can lead them to engage in criminal acts entirely out of character for who they were before the lesions formed. To produce such changes, however, damage needs to be in the right, or should we say, wrong places. Now, a systematic study has identified locations where lesions mean trouble for both the courts and the person suffering them. These locations are distributed around the brain, rather than being bunched together, but all relate to areas responsible for ethical decision-making.
Why people kill, steal, or commit other crimes is a mystery we're far from fully solving, but a few cases are unusually clear. Pseudo-psychopathy, also known as acquired sociopathy, is the name given to cases where brain lesions are considered responsible, or at least one cause among many, for anti-social behavior. In extreme cases, consequences can be horrifying. Charles Whitman developed a brain tumor (a common cause of lesions) and subsequently murdered 16 people, wounding many more, although psychiatrists disagreed on whether the tumor was responsible.
Nevertheless, millions of people get brain tumors or suffer injuries every year. Many experience personality changes, but only a few suddenly turn to crime. No doubt some people are more easily tipped over the edge than others, but the location of damage is thought to be crucial. Harvard's Dr Michael D Fox looked at 17 cases where brain lesions appeared to trigger criminal behavior – 12 of which involved violent crimes – to find commonalities in the affected areas. Most of those involved had no criminal record before their brains were affected, and two others stopped misbehaving after undergoing operations.
To the untrained eye, the lesions Fox observed look to have affected a random assortment of brain parts. Some affected quite large areas, others small ones. There's a fairly even split between the hemispheres, and while the frontal regions are more heavily featured than the rest of the brain, some incidences were in the middle or back.
Nevertheless, the affected areas had more in common than they seem. “All 17 lesions temporally associated with criminal behavior were functionally connected (i.e., positively correlated) to the inferior orbitofrontal cortex and anterior temporal lobes,” Fox and his co-authors write in Proceedings of the National Academy of Sciences. Most also had connections to certain other specific areas. All the areas that were always or most frequently affected were ones activated when making decisions that involve moral choices.
A sample of people with brain lesions but no criminal behavior found most affected parts of the brain unconnected to moral decision-making. The scientists, however, caution against over-interpreting their results. Not everyone with brain lesions in the relevant locations develop criminal behavior, making lesions a risk factor but not a sole cause.