ABSTRACT
Even casual inspection of a rat pressing a lever for electrical stimulation of the medial forebrain bundle (MFB) reveals why this activity has been viewed as a striking example of appetitively motivated behavior. If the stimulation parameters are adjusted to be well above threshold, the rat spends almost all of its time in the vicinity of the lever. When removed from this region, it returns with alacrity. The rat manipulates the lever with unusual vigor and persistence, sometimes bracing its hindpaws, seizing the manipulandum between its forepaws or teeth, and twisting its torso to achieve an optimal grip. If left undisturbed, the rat can maintain this behavior for hours at a time. Only when the strength of the stimulation is reduced does the rat's fatigue become evident. It may then lie down on the cage floor, apparently spent from its exertions. However, should the experimenter restore the stimulation to its former strength and deliver a few free trains, the rat will rise and return to the lever, shaking off its lassitude. If appetitive motivation can be defined as a state that energizes behavior and directs it toward a goal, then surely the state evoked by the stimulation is an instance of it.
