kelly and corbett trained rats to run down the arm of a maze to obtain ESB. following the injection of a dopamine antagonist, higher levels of stimulation were required to maintain the rats' running behavior. activity in the mesolimbic system,and the nucleus accumbens in particular, underlies many types off reward. According to comings and blum,eating and sexual behaviors constitute "natural" situations for the activation of reward circuits, however, can also be actived by "unnatural" situations, including the use addictive drugs and compulsive eating, compulsive sex, or gambling. Observing rats bar-pressing to the point of exhaustion or starvation to stimulate this circuit helps us capture the essence of compulsive and addictive behavior.