Figure 1.

Food pellet self-administration training, extinction of food-reinforced lever responding, and body weight change. (a) Training (first 9 days): mean±SEM number of 35% fat pellets earned and timeout (T.O.) responses on the active lever (total lever presses minus pellets earned) during the training sessions, which occurred on alternate days (one 3-h session per day, every other day). Rats were trained on a fixed-ratio 1 (FR-1) 20-s timeout reinforcement schedule (n=98). (b) Extinction (first 9 days): mean±SEM number of responses on the previously active lever in the presence (n=88) or absence (n=10, experiment 3c) of a discrete tone-light cue. (c) Body weight fluctuations during training and extinction phases (n=98). During the training phase, rats were maintained on 16 g/day of regular chow food and were given 3-h access to food pellets every other day. During the extinction (and reinstatement) phases, food pellets were not available in the self-administration chambers, and rats were maintained on 18–22 g/day of regular chow to maintain stable body weight.