No ventral prefrontal cortex? No problem!

Brain damage - it's not much fun when it's your brain, but for science, it's often good news. While neuroimaging can find the neural correlates of mental processes - areas of the brain which become active during the experience of an emotion, say - lesion studies are often necessary to establish the direction of causality. Just because somewhere in the brain is activated during the experience of fear, for example, doesn't mean that this area is responsible for our feelings of fright; it might just happen to be lighting up as a side effect. Neuroimaging can't tell the difference, but if someone suffers damage to some part of the brain and then becomes fearless, it becomes possible to establish which parts do what. Localizing a function to a certain region of the brain is not the same as understanding it, of course, but it's a start.