Brain responses to heat and pain

Inclusion criteria: Parkinson's Disease Arm 1. Meet the diagnostic criteria of clinically established Parkinson's disease or clinically probable Parkinson disease according to the International Parkinson and Movement Disorder Society diagnostic criteria. 2. Have a Hoehn & Yahr stage of 3 or less. 3. 50 years of age or older. Healthy Elderly Control Arm 1. 50 years of age or older. 2. Do not meet the above criteria for Parkinson's disease. Healthy Young Control 1. 20 years of age or older but less than 50 years. 2. Do not meet the above criteria for Parkinson's disease. Exclusion criteria: 1. Diagnosis of diseases that cause specific chronic pain, such as osteoarthritis, rheumatoid arthritis, irritable bowel syndrome, fibromyalgia, complex regional pain syndrome, multiple sclerosis, and others. 2. Presence of chronic pain. 3. Presence of pain on the day of the visit. 4. History of major depression or bipolar disorder as defined by DSM-IV within the past year, or a history of schizophrenia as defined by DSM-IV in the past. 5. Presence of parkinsonism. 6. Presence of skin lesions, such as burns, on the non-dominant forearm to be stimulated with thermal stimuli. 7. History of alcohol or drug dependency defined by DSM-IV within the past two years. 8. Presence of significant psychiatric symptoms, excitability, or behavioral abnormalities that would make it difficult to comply with the protocol within the past three months. 9. Presence of systemic severe deseases or unstable conditions. 10. Presence of other abnormalities that affect cognitive function, such as infections or metabolic disorders. 11. MMSE score of 23/30 or less indicating cognitive impairment. 12. Any other condition deemed inappropriate by the principal investigator or facility physician.