There is now ample evidence that selective serotonin reuptake inhibitors（SSRIs）and behavior therapy are highly effective methods for treatment of obsessive-compulsive disorder （OCD）. It is,however,still unclear how these interventions improve the symptoms. A large number of recent neuroimaging studies using PET, SPECT and fMRI have found that abnormally high activity occurs throughout the frontal cortex and subcortical structures in OCD, and that this hyperactivity decreased after successful treatment using either SSRIs or behavior therapy. In the future, it is expected that assessment of brain function before treatment will enable the prediction of treatment response.
 Evidence from recent neuroimaging studies also suggests that the orbitofronto-striatal model may not be sufficient to explain the brain basis of OCD, and that broader regions, including the dorsolateral prefrontal and posterior regions, might be involved in the pathophysiology of OCD. Furthermore, the fact that OCD is heterogeneous, and may include different neural systems related to clinical factors, should also be considered.
 Finally, it is still arguable whether changes in glucose metabolism or blood flow,which are the basis for neuroimaging studies, essentially reflect the pathophysiology of OCD. Thorough neurobiological studies incorporating neuropsychology, structural imaging, functional imaging and molecular imaging should be performed in order to facilitate the development of treatment strategy based on a comprehensive understanding of OCD pathophysiology.