Depression is known to be a common symptom of Parkinson's disease, but remains untreated for many patients, according to a new study. In fact, depression is the most prevalent non-motor symptom of Parkinson's, a chronic neurodegenerative disorder typically associated with movement dysfunction. Among those with high levels of depressive symptoms, only one-third had been prescribed antidepressants before the study began, and even fewer saw social workers or mental health professionals for counseling.