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Obsessive Compulsive Disorder: Background and Brain Etiology

By: , Posted on: October 5, 2016

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This excerpt was taken from the article Obsessive–Compulsive Disorder by V.L. Beckner

Patients suffering from obsessive–compulsive disorder (OCD) experience a combination of anxiety-producing obsessive thought patterns and related compulsive behaviors designed to reduce the distress associated with the obsessions.

Obsessions are recurrent thoughts, impulses, or images that are threatening because they are perceived as either unacceptable or leading to a dreaded outcome, and thus cause marked anxiety. Common obsessional ‘themes’ include contamination (thinking one has contacted dangerous germs or toxins), aggression (image or urge to drive into oncoming traffic or stab one’s spouse), accidental harm (fear that one has hit a pedestrian or doubting whether one turned off the stove), blasphemy (thinking one has offended God by doing a religious ritual incorrectly), and sexuality (intrusive images of having sex with a child or parent). Sometimes an obsession is vague, yet still evokes a looming sense of danger: a ‘bad feeling’ that occurs during an action, or the inexplicable sense that a behavior has not been done correctly. Multiple types of obsessions are found in most affected individuals and can change over time.

Compulsions include behaviors (e.g., hand washing, checking, ordering, or arranging things) and mental actions (e.g., praying, counting, repeating words silently) that are aimed at preventing or neutralizing the threat associated with the obsession, and thus temporarily reduce anxiety. This relief from the distress is highly reinforcing, resulting in the persistent use of compulsions. Compulsive behaviors are often repeated (checking the stove 15 times), or have to be performed according to rules that must be applied rigidly (a sterilization ritual for plates and silverware before meals).

Sometimes compulsions are ‘logically’ linked to the obsessions, as in the case of washing one’s hands in response to a contamination obsession, or driving back to a spot where one fears they may have hit someone. Done once, such behavior might seem reasonable; it is the repetitive, time-consuming, and rigid quality that distinguishes compulsions. Sometimes, there is no ‘logical’ action to prevent the obsessional threat, so compulsions develop that are more akin to superstitious rituals. For example, going through doorways can often trigger an obsession (‘bad feeling’). Given no clear antidote to the vague threat, individuals may develop a ritualized compulsion aimed at neutralizing the obsession in some magical way. This might involve having to go through the door on the left side, touching both sides of the threshold 3 times, or passing through the doorway repeatedly until it is accomplished without any ‘bad thoughts.’

Individuals with OCD generally have some degree of insight that their symptoms are excessive or unreasonable. Nonetheless, the disorder is time-consuming, distressing, and severely impairing within the realms of both social and occupational functioning. It is also associated with increased risk of suicide. OCD has an estimated lifetime prevalence in the general US population of 2–3%, and is equally common in both males and females. The age of onset follows a bimodal distribution: early onset (prepubescent, the majority of cases) and late onset (early 20s). Early-onset cases are more likely to be male, have a family history of OCD, greater symptom severity, and cooccurring tics, OCD spectrum (discussed in section Differential Diagnosis), and disruptive behavioral disorders (e.g., attention deficit hyperactivity disorder).

Differential Diagnosis

It is important to distinguish OCD from worry, intrusive thoughts, and compulsions seen in everyday life. OCD obsessions are experienced as unwanted and anxiety-producing, whereas worry functions more as a mental coping strategy that provides a sense of control and preparation for a perceived future threat. Intrusive thoughts (i.e., suddenly envisioning a family member falling off a cliff while hiking together) are common, but in OCD they occur at a higher frequency, and are experienced as having unusual importance, so are more distressing to the affected individual. Compulsive behaviors are also frequently seen in normal populations in the form of superstitious behavior and repetitive checking. The diagnosis of OCD is made only if they are time consuming or if they result in significant psychosocial impairment or distress.

There are a number of disorders that share the features of OCD, and are sometimes considered as ‘OCD spectrum disorders.’ Disorders such as body dysmorphic disorder, hypochondriasis, and hoarding and eating disorders include obsessive-like fears (that one has a serious illness or is fat), but the thoughts are not experienced themselves as highly intrusive and inappropriate. Dermatillomania (skin picking) and trichotillomania (hair pulling) have repetitive behaviors that may bring some anxiety relief, but they are neither triggered by obsessions nor have the magical or ritualistic quality of OCD compulsions. Although impulse-control disorders such as kleptomania, pyromania, and pathological gambling also have recurrent thoughts and behaviors that are difficult to resist, the drive tends to be more pleasure-seeking than distress reducing.

Schizophrenia is often characterized by strongly held beliefs that are clearly false (delusions) as well as by stereotyped behaviors. Individuals with OCD, however, generally show considerable insight into their symptoms. In major depression, the depressed individual may have distressing, repetitive thoughts, but these are rarely resisted, and are often focused on a past incident rather than on a current or future threat. Although it has a similar name, obsessive–compulsive personality disorder is actually quite different from OCD. Obsessive–compulsive personality disorder does not involve obsessions or compulsions; rather, it is characterized by a pervasive pattern of maladaptive orderliness, perfectionism, and control.

Other disorders may mimic OCD. Tics and stereotyped movements are similar to compulsions in their appearance but not in their function. Generally, the cognitive elements involved in OCD compulsions are much more complex, whereas in tics and stereotypic movements, the individual does not report any specific reason for the behavior, but only a nonspecific tension that builds until the behavior is performed. Of note, Tourette’s syndrome and OCD are frequently cooccurring disorders, and individuals with Tourette’s should be routinely asked about the presence of obsessions and compulsions.


There is converging evidence that OCD involves dysfunction of the corticostriatal-thalamic circuits, which help integrate cognitive and sensorimotor functions, and in particular initiate automatic, procedural behaviors. The high cooccurence of OCD with Tourette’s – a disorder involving cortical and striatal pathways – is suggestive of a similar etiology. There are also data supporting an association between an autoimmune response to Group A β-hemolytic Streptococcus affecting the striatal regions, and the acute emergence of OCD, often with tic symptoms (including Tourette’s). The term pediatric autoimmune neuropsychiatric disorder associated with Streptococcus refers to a group of children with this presumed immunological etiology. The role of serotonin in the corticostriatal-thalamic circuits is thought to be important, and several studies suggest that serotonin reuptake inhibitors may normalize activity in these pathways. Medications that boost serotonin activity reliably reduce OCD symptoms. Research also suggests that abnormalities in the glutamate and dopamine systems are involved in OCD as well.

The evidence for a genetic contribution is supported by the monozygotic twin studies showing a concordance rate from 63% to 87%, and first-degree relatives showing rates of OCD in the range of 10–22.5%. No candidate gene has been identified that can reliably account for the broad phenotype of OCD. Animal models of OCD, such as those found naturally in dogs or induced in laboratory mice, identify the potential genes for further study.

From the standpoint of neuroimaging, OCD is one of the most investigated illnesses in the anxiety cluster. As of yet, it remains impossible to attribute causality to particular brain structures in the cognitions and clinical features of OCD. In animal models, abnormalities in the orbitofronto-striatal circuits are associated with an impaired ability to modify behavior in response to new information, for example: impaired inhibition of previously important, but now inappropriate response to stimuli. Humans with injuries to the striatum, or areas to which it projects, often develop obsessive –compulsive behaviors. Nevertheless, no consistent structural abnormality has been identified in patients meeting the criteria for OCD. This may suggest that the causative abnormalities are present at the level of a system or network, not at the level of isolated neuroanatomical structures, or because of a marked heterogeneity within the diagnosis. Illnesses with components of compulsive and impulsive behaviors, such as Tourette’s syndrome and trichotillomania, tend to occur in comorbidity with OCD, or cluster with OCD within families. Further research into these disorders of overlapping endophenotype may serve to illuminate the rest of the OCD picture as it relates to the brain structure.

This excerpt was taken from the article Obsessive–Compulsive Disorder by V.L. Beckner, University of California San Francisco, and San Francisco Group for Evidence-Based Psychotherapy, San Francisco, CA, USA. The article is included in the Encyclopedia of the Neurological Sciences (Second Edition) and the forthcoming Reference Module in Neuroscience and Biobehavioral Psychology. Launching in November 2016 the Reference Module combines thousands of encyclopedic and comprehensive articles from Elsevier’s Major Reference Works into one interdisciplinary resource on ScienceDirect. The articles are continuously reviewed and updated to ensure researchers and students are up to date with the latest in science. Learn more about the Reference Module here.

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