Prospective Neuroimaging Investigation of Idiopathic REM Sleep Behavior Disorder

Inclusion Criteria: iRBD group: * A diagnosis of RBD according to the international classification of sleep disorders-2 (ICSD-2) criteria * No current neurological diseases related with RBD * Male or female aged from 30 to 80 years old at screening * Subject enrolled voluntarily and understood the contents of the study PD group: * A diagnosis of PD according to the UK Brain Bank Diagnostic Criteria * A diagnosis of RBD according to the international classification of sleep disorders-2 (ICSD-2) criteria * Male or female aged from 30 to 80 years old at screening * Subject enrolled voluntarily and understood the contents of the study Control group: * No current neurological or psychiatric diseases related with RBD * Male or female aged from 30 to 80 years old at screening * Age and sex matched with those of subjects in iRBD group * Subject enrolled voluntarily and understood the contents of the study Exclusion Criteria: * Clinically significant cognitive decline unable to follow the study (Mini-mental state examination \[MMSE\] score less than 20) * History of psychiatric illnesses (ex. depression) * Unable to walk and cooperate to the examination * Unable to take magnetic resonance imaging or positron emission tomography * Existence of illness or problems which makes difficult to be enrolled to the study judged by clinicians