D4, or D4 receptor, is a type of dopamine receptor found in the brain. It plays a crucial role in regulating various functions, including mood, motivation, and movement. D4 receptors are part of the dopamine receptor family and are primarily associated with the central nervous system. Research has shown that D4 receptors may be linked to certain psychological conditions, such as attention deficit hyperactivity disorder (ADHD) and schizophrenia. Understanding the function of D4 can help in developing targeted treatments for these disorders, as well as improving our knowledge of how dopamine influences behavior and cognition.