Obsessive Compulsive Disorder (OCD) is a disease of the mind characterized in the DSM-5 as having obsessions and compulsions, they must also be intrusive, repetitive, and impede normal functioning. The individual with OCD is unable to ignore the persistent thought patterns. This disorder causes ritualistic behavior; these rituals must take up at least one hour of the day, upon performance of these rituals the anxiety is reduced.

In America, about 2.3% of the population has OCD between the ages of 18 and 54 years old. The obsession can be anything from thoughts of if something is not done correctly a family member will die, or if hands are not washed enough the individual may get deathly ill. A compulsion, similar to the obsession, can be pretty much anything; from the stereotype of excess washing of hands, to locking doors and even saying a sentence over and over again until it "feels right". The compulsion is in response to the obsessive thought. The afflicted individual may have complete awareness that what they are doing is unreasonable, however, if they do not do the ritual intense anxiety can over come them.

In terms of anatomy, one theory is that the looping thought is caused by a malfunction in the communication of the orbital frontal gyrus (involved in cognitive decision making) to the cingulate gyrus (helps with emotion processing) striatum (motor/reward system), globus pallidus (voluntary movement) finally the thalamus (sense processing, with exception to olfactory) then back to the frontal cortex. Treatment usually consists of selective serotonin reuptake inhibitors, and a combination of talk psychotherapy. Cognitive behavioral therapy seems to show promise in helping OCD. Research supports a combination of talk therapy along with SSRIs for treatment.