OCD has a lifetime prevalence of 1–3% worldwide [17]. The disease course is often chronic [18] and associated with significant functional impairments, financial costs and increased mortality [19–20]. OCD is characterized by compulsions (repetitive, ritualized behaviors or mental acts) that are often performed in response to obsessions (recurrent, intrusive, unwanted, distressing, time-consuming thoughts) that generate fear and anxiety (with or without autonomic symptoms) or doubts/uncertainty. At the same time, there is phenotypic heterogeneity. For example, the content of obsessions and expression of compulsions can vary dramatically between individuals, ranging from concerns about contamination or harm to preoccupation with symmetry or taboo thoughts [21]. In addition, some patients do not have obsessions but perform their rituals to relieve or achieve specific tactile, visual or auditory sensations, a sense of completeness or a just-right feeling (i.e., sensory phenomena [22]). Repetitive behaviors originally undertaken to neutralize obsessions may, over time, become habits that are elicited by stimuli rather than by intrusive thoughts [23]. Some patients carry out compulsive behaviors because they feel rewarding and almost pleasurable, rather than to elicit a sense of relief [24]. Finally, higher-order cognitive alterations, such as executive dysfunction, may trigger or perpetuate compulsive behaviors for some patients [25].
