Researchers are studying the brain's striatum, which not only is responsible for controlling how we move, but also contributes to the brain's decision-making and the initiation of action. Nearly 95 percent of the cells that make up the striatum are known as medium spiny neurons (MSN), which is associated with many psychiatric and neurodegenerative diseases, including Parkinson's disease, Huntington's disease, schizophrenia, drug addition and ADHD.