Searching for the neural causes of criminal behavior.

All behavior is proximally caused by the brain, but the neural causes of most complex behaviors are still not understood. Much of our ignorance stems from the fact that complex behavior depends on distributed neural control. Unlike a reflex, where the arc from sensation to action can be traced through a few synapses, most volitional behavior involves a dense causal web through which stimuli, memories, beliefs, and other factors exert their effects. Disruption anywhere in this causal web can produce effects that are difficult to trace back to their origin. Against this background, the finding that focal lesions of the ventromedial prefrontal cortex could lead to immoral and even criminal behavior generated considerable surprise and interest (1, 2). While a number of rare cases have now been described in whom a focal lesion caused criminality, these are neither very consistent (the lesions occur in several different anatomical locations) nor at all reliable (only a small fraction of patients, for any lesion location, show criminal behavior). To explain the effects of a lesion on criminal behavior, we need to understand what it is that the lesion does to the rest of the brain, a network-level understanding of lesion effects now provided by the new study of Darby et al. in PNAS (3).