Performance as a function of delays to reinforcement in animals trained preoperatively Response-reinforcer delays systematically lowered the rate of free-operant instrumental responding, and this relationship was altered in AcbC-lesioned rats, even allowing for differences in response-collection delays experienced postoperatively. Lesions were made after initial training; postoperative experienced delays and response rates are plotted. (Compare Figure 7, in which rats had no preoperative experience of the task.) (a) The rate of responding on the active lever in session 24 (the 10th postoperative session; compare Figure 7) is plotted against the programmed response-reinforcer delay. AcbC-lesioned rats responded significantly less than shams in the 20 s delay condition (* p = .025). (b) Responding on the active lever in session 24 (the 10th postoperative session) plotted against the experienced response-to-reinforcer-collection delays for postoperative sessions up to and including session 24 (vertical error bars: SEM of the square-root-transformed number of responses in session 24; horizontal error bars: SEM of the experienced response-collection delay). The gradients of the two lines differed significantly (# p = .015; see text), indicating that the relationship between experienced delays and responding was altered in AcbC-lesioned rats, compared to sham-operated controls.