Effects of anterior medial forebrain bundle lesions on self-stimulation with two different operant responses

Rats immobilized in a restraining cage were trained to move their tails back and forth using lateral hypothalamic stimulation as reinforcement. The same rats were also trained to bar press in an ordinary cage for the same reinforcement. Following lesions in the medial forebrain bundle anterior to the stimulation site the stimulation no longer appeared to be positively reinforcing when the animals were tested on the tail movement task. When these subjects were tested on bar pressing, the stimulation still appeared to be reinforcing. Various interpretations of the data, including the possibilities that the lesions changed the rats' emotional responsiveness, and that a different set of fibers within the medial forebrain bundle mediates the reinforcement of each of the two tasks were considered.