My interest in addiction is an outgrowth of my research on analgesic drugs, many of which are addicting. Addiction represents a dysfunction of decision making. It results from exposure of the brain to substances that act upon the neural circuits that assess the reinforcing value of action outcomes and that regulate motivation. Current research in my laboratory utilizes in vivo and in vitro electrophysiology, behavioral pharmacology and human functional imaging to study mesolimbic circuits involved in goal directed behaviors. Our particular focus is on how opioid regulation of synaptic function modulates reward seeking and response to punishment.