We all have habits and mannerisms, and some of these are strong and urgent. But for the most part, these are not intrusive behaviors; they are blended into our lives, give us personality, and form a background on which we build the much larger part of our cognitive activities. Even when we engage in rituals, they can be like games, as when children avoid stepping on cracks in the sidewalk. In people who suffer from obsessive-compulsive disorder (OCD), such “habits,”“mannerisms,” and “rituals” are out of control.

The name, OCD, comes from the hallmark signs and symptoms of the disease, which affect both cognition and motor behavior: obsessions, thoughts that repeat over and over again, unwanted but insistent; and compulsions to act, to repeat fragments of behavior over and over in ritualistic, stereotyped succession. Typically, particular compulsive acts are carried out in response to a particular obsession, as if to neutralize the anxiety and negative affect associated with that obsession. The most common of these obsessions and compulsions involve checking (going back over a behavior repeatedly in response to obsessive self-doubts whether it was done, and done just right), washing (for example, washing the hands until they bleed in response to the “obsession” that they are dirty), ordering (straightening up, like a child having to line up the shoes in his closet over and over, or having to put them in sets of three), and fears of performing aggressive or untoward behaviors and repeated attempts to prevent this.