This document compares the cognitive changes in mild cognitive impairment (MCI), Alzheimer's disease, and Parkinson's disease. MCI involves mild memory loss that does not interfere with daily life. Parkinson's disease causes tremors and movement difficulties due to dopamine loss. Alzheimer's disease is the most common dementia in older adults and involves severe memory loss and cognitive decline. While there are no cures for these conditions, treatments can help manage symptoms for a time. All three diseases have significant effects on patients and their families.