The goal of this study is to learn more about the changes in the brains of patients with cognitive impairment (MCI) and Alzheimer's Disease (AD). The main questions the study aims to answer are: 1. What findings can be used to earlier detect patients that will develop Alzheimers? 2. Which differences are seen between healthy and cognitively impaired patients? 3. Which differences are seen between patients with Alzheimers disease? Participants will undergo: * Cognitive tests * Magnetic resonance imaging (MRI) * Electroencephalography (EEG) * Blood sample collection * Fecal sample collection * A randomized group will undergo polysomnography analysis.