This study aims to understand three brain disorders: Alzheimer's Disease, Lewy Body Dementia, and Parkinson's Disease. It involves using different medical tests like **MRIs** (a type of brain scan), **PET scans** (which show how the brain uses sugar), and **polysomnographs** (tests that check sleep patterns). Participants will have health check-ups, memory and thinking tests, and even a **cerebrospinal fluid** test, which involves taking a small sample of the fluid around the brain and spine, if they agree.

• The study requires participants to have a partner (like a family member) who can help.
• Participants should be on stable cognitive medication for at least four weeks before joining.
• Pregnant women or those with severe kidney problems cannot participate.

Everyone involved will have a detailed medical review, and their partners will also provide information. This study helps find ways to tell these illnesses apart, which can improve diagnosis and treatment in the future.