region of the left hemisphere. It is unclear whether genetics plays a role; however, there are many neurochemical and hormonal changes in individuals with depersonalization disorder. DPDR may be associated with dysregulation of the hypothalamic-pituitary-adrenal axis, the area of the brain involved in the "fight-or-flight" response. Patients demonstrate abnormal cortisol levels and basal activity. Studies found that patients with DPDR could be distinguished from patients with clinical depression and posttraumatic stress disorder. The vestibular system may also play a role in DPDR. The vestibular system helps control balance, spatial orientation, motor coordination, but also plays a role in self-awareness. Disruption to this system can potentially cause a feeling of detachment from surroundings. Several studies have shown that patients with peripheral vestibular disease are also more likely to have dissociative symptoms when compared to healthy individuals. Dissociative symptoms are sometimes described by those with neurological diseases, such as amyotrophic lateral sclerosis, Alzheimer's, multiple sclerosis (MS), etc., that directly affect brain tissue. Diagnosis Assessment Diagnosis is based on the self-reported experiences of the person followed by a clinical assessment. Psychiatric assessment includes a psychiatric history and some form of mental status examination. Since some medical and psychiatric conditions mimic the symptoms of DPDR, clinicians must differentiate between and rule out the following to establish a precise diagnosis: temporal lobe epilepsy, panic disorder, acute stress disorder, schizophrenia, migraine, drug use, brain tumor or lesion. No laboratory test for depersonalization-derealization disorder currently exists. As patients with dissociative disorders likely experienced intense trauma in the past, concomitant dissociative disorders should be considered in patients diagnosed with a stress disorder (i.e. PTSD or acute stress disorder). The diagnosis of depersonalization disorder can be made with the use of the following interviews and scales: The Structured Clinical Interview for DSM-IV Dissociative Disorders (SCID-D) is widely used, especially in research settings. This interview takes about 30 minutes to 1.5 hours, depending on individual's experiences. The Dissociative Experiences Scale (DES) is a simple, quick, self-administered questionnaire that has been widely used to measure dissociative symptoms. It has been used in hundreds of dissociative studies, and can detect depersonalization and derealization experiences. The Dissociative Disorders Interview Schedule (DDIS) is a highly structured interview which makes DSM-IV diagnoses of somatization disorder, borderline personality disorder and major depressive disorder, as well as all the dissociative disorders. It inquires about positive symptoms of schizophrenia, secondary features of dissociative identity disorder, extrasensory experiences, substance