Obsessive-Compulsive Disorder (OCD)
Causes Of OCD
The fact that OCD patients respond well to specific medications suggests the disorder has a neurobiological basis. For that reason, OCD is no longer attributed to attitudes a patient learned in childhood-for example, an inordinate emphasis on cleanliness, or a belief that certain thoughts are dangerous or unacceptable. Instead, the search for causes now focuses on the interaction of neurobiological factors and environmental influences. It is believed that people who develop OCD have a biological predisposition to react strongly to stress, that this reaction takes the form of intrusive, distressing thoughts, and that these thoughts lead to more anxiety and stress, eventually creating a vicious circle the person cannot escape without help.
Brain imaging studies using a technique called positron emission tomography (PET) have compared people with and without OCD. Several groups of investigators have obtained findings from PET scans suggesting that OCD patients have patterns of brain activity that differ from those of people without mental illness or with some other mental illness. Brain imaging studies of OCD showing abnormal neuro-chemical activity in regions known to play a role in certain neurological disorders suggest that these areas may be crucial in the origins of OCD. In addition, PET scans show that in patients with OCD, both behavioral therapy and medication produce changes in the caudate nucleus, a part of the brain. This is graphic evidence that both psychotherapy and medication affect the brain.
Persons with OCD use different brain circuitry in performing
a cognitive task than people without the disorder.
( Rauch SL, Savage CR, Alpert NM, et al. Probing striatal function in obsessive-compulsive disorder: a PET study of implicit sequence learning. Journal of Neuropsychiatry and Clinical Neuroscience, 1997; 9(4): 568-73.)
Recent preliminary studies of the brain using magnetic resonance imaging showed that the subjects with obsessive-compulsive disorder had significantly less white matter than did normal control subjects, suggesting a widely distributed brain abnormality in OCD. Understanding the significance of this finding will be further explored by functional neuroimaging and neuropsychological studies.
Symptoms of OCD are seen in association with some other neurological disorders. There is an increased rate of OCD in people with Tourette's syndrome, an illness characterized by involuntary movements and vocalizations. Investigators are currently studying the hypothesis that a genetic relationship exists between OCD and the tic disorders.
Other illnesses that may be linked to OCD are trichotillomania (the repeated urge to pull out scalp hair, eyelashes, eyebrows or other body hair), body dysmorphic disorder (excessive preoccupation with imaginary or exaggerated defects in appearance), and hypochondriasis (the fear of having--despite medical evaluation and reassurance--a serious disease). Genetic studies of OCD and other related conditions may enable scientists to pinpoint the molecular basis of these disorders.
Other theories about the causes of OCD focus on the interaction between behavior and the environment and on beliefs and attitudes, as well as how information is processed. These behavioral and cognitive theories are not incompatible with biological explanations.
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