In a work of systematic biology that advances the field, University of Alabama at Birmingham (UAB) researchers have identified 16 distinct cell populations in a complex area of the midbrain called the ventral tegmental area, or VTA. The VTA is important for its role in the dopamine neurotransmission involved in reward-directed behavior. Substance use disorders involve dysregulation of these reward circuits, leading to repeated drug-seeking despite adverse consequences. These include more than 100,000 drug overdose deaths in the United States in the most recent year. The VTA also has a role in several other neuropsychiatric disorders. Thus, expanding knowledge of VTA function is a start to explaining the mechanisms for substance use disorders involving drugs like cocaine, alcohol, opioids, and nicotine, or psychiatric disorders like schizophrenia and attention deficit hyperactivity, or attention-deficit hyperactivity disorder (ADHD).