It has all the makings of a classic B movie scene. A gunman puts a pistol to the victim’s forehead, and the screen fades to black before a loud bang is heard. A forensic specialist who traces the bullet’s trajectory would see it traversing the brain’s prefrontal cortex—a central site for processing decisions. The few survivors of usually fatal injuries to this brain region should not be surprised to find their personalities dramatically altered. In one of the most cited case histories in all of neurology, Phineas Gage, a 19th-century railroad worker, had his prefrontal cortex penetrated by an iron rod; he lived to tell the tale but could no longer make sensible decisions. Cocaine addicts may actually self-inflict similar damage. The resulting dysfunction may cause even abstaining addicts to crave the drug any time, say, the thudding bass of a techno tune reminds them of when they were stoned.
Even people who do not use illicit drugs or get shot in the head have to contend with the