Responding on the active lever during the four extinction sessions is represented in Fig. 2A. ANOVA revealed significant main effects of Session [F(3,103) = 47.6, p<0.001], Group [F(2,103) = 16.3, p<0.001] and Group x Session interaction [F(6,103) = 11.2, p<0.001]. Newman-Keuls post hoc tests showed that both the H-RI and L-RI rats responded significantly more on the active lever in Sessions 1 and 2 than in Session 4 (p<0.001). The NR rats did not show responding differences across Sessions. In Session 1, the H-RI rats responded significantly more than the L-RI and NR rats (p<0.001), and the L-RI rats responded significantly more than the NR rats (p<0.001). In Session 2, both the H-RI and L-RI rats had significantly more responding than the NR rats (p<0.05), with no difference between the H-RI and L-RI groups.
