Symptom-specific neuroimaging abnormalities include the hyperactivity of caudate and ACC in checking rituals, while finding increased activity of cortical and cerebellar regions in contamination-related symptoms. Neuroimaging differentiating content of intrusive thoughts has found differences between aggressive as opposed to taboo thoughts, finding increased connectivity of the amygdala, ventral striatum, and ventromedial prefrontal cortex in aggressive symptoms, while observing increased connectivity between the ventral striatum and insula in sexual or religious intrusive thoughts.Another model proposes that affective dysregulation links excessive reliance on habit-based action selection with compulsions. This is supported by the observation that those with OCD demonstrate decreased activation of the ventral striatum when anticipating monetary reward, as well as increased functional connectivity between the VS and the OFC. Furthermore, those with OCD demonstrate reduced performance in Pavlovian fear-extinction tasks, hyperresponsiveness in the amygdala to fearful stimuli, and hyporesponsiveness in the amygdala when exposed to positively valanced stimuli. Stimulation of the nucleus accumbens has also been observed to effectively alleviate both obsessions and compulsions, supporting the role of affective dysregulation in generating both. Neurobiological
From the observation of the efficacy of antidepressants in OCD, a serotonin hypothesis of OCD has been formulated. Studies of peripheral markers of serotonin, as well as challenges with proserotonergic compounds have yielded inconsistent results, including evidence pointing towards basal hyperactivity of serotonergic systems. Serotonin receptor and transporter binding studies have yielded conflicting results, including higher and lower serotonin receptor 5-HT2A and serotonin transporter binding potentials that were normalized by treatment with SSRIs.
The vast majority of people who thought that they were possessed by the devil did not have hallucinations or other "spectacular symptoms" but "complained of anxiety, religious fears, and evil thoughts. ": 213  In 1584, a woman from Kent, England, named Mrs. Davie, described by a justice of the peace as "a good wife", was nearly burned at the stake after she confessed that she experienced constant, unwanted urges to murder her family. : 213 The English term obsessive–compulsive arose as a translation of German Zwangsvorstellung (obsession) used in the first conceptions of OCD by Carl Westphal. Westphals description went on to influence Pierre Janet, who further documented features of OCD. In the early 1910s, Sigmund Freud attributed obsessive–compulsive behavior to unconscious conflicts that manifest as symptoms. Freud describes the clinical history of a typical case of "touching phobia" as starting in early childhood, when the person has a strong desire to touch an item. In response, the person develops an "external prohibition" against this type of touching. However, this "prohibition does not succeed in abolishing" the desire to touch; all it can do is repress the desire and "force it into the unconscious." Freudian psychoanalysis remained the dominant treatment for OCD until the mid-1980s, even though medicinal and therapeutic treatments were known and available, because it was widely thought that these treatments would be detrimental to the effectiveness of the psychotherapy. : 210–211  In the mid-1980s, this approach changed, and practitioners began treating OCD primarily with medicine and practical therapy rather than through psychoanalysis.