Decision-making is a complex process involving choices among actions based on the subjective evaluation of the relative costs and benefits of each option. Disruption of decision-making processes is a prominent feature of many neuropsychiatric disorders, including drug addiction, ADHD and obsessive-compulsive disorder, and is manifested as maladaptive decision making and poor reinforcement learning. In rodents, instrumental learning tasks can be used to assess decision making, and have revealed an important role of cortico-basal ganglia circuits in the mechanisms underlying decision-making processes. Dr. Susan Ferguson’s laboratory employs a novel chemical-genetic approach that uses viral vectors to express artificial, engineered G-protein coupled receptors (known as DREADD receptors) in discrete neuronal cell populations in rodents (e.g. striatonigral ‘direct’ pathway neurons, striatopallidal ‘indirect’ pathway neurons, populations of cortical neurons) in combination with rodent operant learning tasks in order to study the role of the cortex and the striatum in decision making and reinforcement learning.