Studies by researchers at Gladstone Institutes and Salk Institute have identified and created brain-wide maps of neurons that connect with the basal ganglia. This region of the brain is involved in movement and in making decisions. Two types of neurons, direct-pathway medium spiny neurons (dMSNs) and indirect-pathway medium spiny neurons (iMSNs), appear to act as opposing forces. That is, dMSNs initiate movement, like the gas pedal in a vehicle, while iMSNs inhibit movement, much like the brake. A dysfunction of dMSNs or iMSNs is associated with addictive or depressive behaviors, respectively. Researchers believe these findings are important because they provided a link between the physical neuronal degeneration seen in movement disorders, such as Parkinson’s, and some of the disease’s behavioral aspects (e.g., decision-making). These findings provide a framework for guiding future studies of basal ganglia circuit function.