**Study Overview:** This study uses a special brain scan called **PET imaging** to learn how the brain changes as we age or with diseases like **Alzheimer's**, **Parkinson's**, and other brain disorders. PET imaging, or Positron Emission Tomography, helps doctors see tiny details in the brain. It’s like using a super-powered camera to take detailed pictures. The study aims to understand how small brain areas change with age and in certain diseases, which can help doctors diagnose these conditions earlier. **Who Can Join:** Volunteers who are between 18 and 90 years old and are generally healthy can join. Some participants may have mild memory problems, **ALS** (a nerve disease), or psychotic disorders. People with certain medical conditions or who take specific medications might not be eligible. **What Participants Will Do:** - Participants will have **PET and MRI scans**, which are safe ways to look at the brain. - They will also take tests that check memory, mood, and movement. **Key Points:** - **Duration & Visits:** Participants need to visit the study site for the scans and tests; the exact number of visits will be explained. - **Risks:** Some might feel uncomfortable during the scans, but the procedures are generally safe. - **Compensation:** Participants might receive compensation for their time and travel. This study will help create better tools for diagnosing and treating brain diseases in the future.