Autonomic Involvement in Patient With Cognitive Decline

This study is examining how the nervous system that controls automatic body functions (the autonomic nervous system — which regulates heart rate, blood pressure, and digestion) is affected in people with cognitive decline and dementia, including Alzheimer's disease, Parkinson's-related dementia, and Lewy body dementia. **You may be eligible if...** - You are between 50 and 85 years old - You have a diagnosis of dementia (Alzheimer's, Parkinson's dementia, or Lewy body dementia) or mild cognitive impairment - You are physically able to stand upright **You may NOT be eligible if...** - You have diabetes - You have significant eye problems or peripheral neuropathy - You have severe cognitive decline (unable to cooperate with testing) - You have heart disease or a language barrier - You have cancer or other conditions known to cause cognitive problems independently Talk to your doctor to see if this trial is right for you.