Background: Approximately 40% of patients with Parkinson's disease (PD) have cognitive impairments. There is a lack of consensus as to the extent to which psychiatric symptoms, depression, age at disease onset, disease duration, and medication is related to the type and severity of cognitive impairment. This discrepancy can in part be caused by the lack of distinction between patients with different motor symptoms and disease severity.

Objective: To identify the extent to which psychiatric symptoms, depression, age at disease onset, disease duration, and medication is related to the severity and type of cognitive dysfunction in patients with idiopathic PD categorized according to motor symptoms and disease severity.

Methods: the population of patients with PD in the old county of Aarhus is described on the background of medical records, and stratified in accordance to age, sex and cardinal symptoms. Through proportional allocation a sample of a minimum of 50 patients with PD is drawn from the population. The patients and 30 healthy matched controls will undergo comprehensive neuropsychological assessment including tests of language, memory, executive function, and visuospatial function. Furthermore, all participants will be screened for depression (Geriatric Depression Scale) and psychiatric symptoms (Neuropsychiatric Inventory and Symptom Checklist). The patients will be categorized in accordance with their motor symptoms via cluster analysis for the purpose of analyzing the effect of psychiatric symptoms, depression, and age of disease onset, disease duration, and medication on cognition.

Inclusion Criteria:

• Idiopathic Parkinson's in accordance to UK Parkinson's Disease Society Brain Bank Clinical Diagnostic Criteria,
• Born and raised in Denmark ,
• >50 years

Exclusion Criteria:

• Cerebrovascular disease,
• Dementia not caused by Parkinson's Disease,
• Metabolism anomaly,
• Abuse of drugs, medication or alcohol,
• History of head injuries,
• Severe psychiatric disorder, excluding depression,
• Resident outside the region of Aarhus h) DBS -

77 patients with PD and 30 healthy control participants