The lumping together of the seven deadly sins—pride, covetousness, jealousy, sloth, lust, gluttony, and anger—is, of course, a theological categorization rather than a medical nosology. Nevertheless, these seven sins are oddly reminiscent of various symptoms of a common medical disorder—one that has received increasing neuroscientific investigation in recent years—obsessive-compulsive disorder (OCD). Is such a parallel between sin and symptom purely coincidental, or is modern neurobiology able to provide a more coherent explanation?

Interestingly, the term “obsession” derives from the Roman Catholic concept of obsession—a state of being possessed by the devil. Indeed, obsessions—defined as recurrent intrusive and senseless thoughts and images—are some of the most overwhelming and distressing of psychiatric symptoms. While it is true that hallucinations and delusions lead to a loss of contact with reality, people with obsessions suffer from the very fact that they cannot resist ideas that they know full well to be irrational. Thus, OCD sufferers find themselves having to perform compulsions—recurrent rituals that relieve anxiety—but which are not realistically connected to the preceding obsessions or are clearly excessive.