Fig. 6. Effect of laparotomy on frequency of interreinforcement intervals (IRIs) greater than 20, 50, or 100 s for sucrose-maintained responding. The percentage of IRIs exceeding 20, 50, or 100 s of the total number of IRIs throughout the session is shown after sham surgery or abdominal incision. BSL =baseline data that were obtained by averaging the data from the five sessions immediately before surgery. * Significantly different from baseline, P ≤ 0.05. # Significantly different from sham, P ≤ 0.05.