Figure 3: Acquisition, Escalation, 1^st h Escalation, and Extinction in^{Experiment 2}.

(A) Mean (±SEM) number of active and inactive lever presses for females and males across the 1-h sessions during Experiment 2 acquisition. The difference between active and inactive lever pressing change was significant for both males and females *(both p < .0001). The difference between the active and inactive lever pressing change across sessions was greater in females than males ^(p < 0.05). (B) Mean (±SEM) number of active lever presses for ShA and LgA females and males across sessions during Experiment 2 escalation. The LgA group pressed the active lever more on session 1 than the ShA group #(p < .0001). Females had more active lever presses than males overall ^(p < .05). LgA rats escalated intake across sessions *(p < .01), but ShA rats did not (p > .05). (C) Mean (±SEM) number of active lever presses for ShA and LgA females and males across sessions during the 1^st h of Experiment 2 escalation. Females had more active lever presses than males overall ^(p < .05). LgA rats escalated intake across sessions *(p < .001), but ShA rats did not (p > .05). (D) Mean (±SEM) number of active lever presses for ShA and LgA females and males across sessions during Experiment 2 extinction. LgA rats pressed the active lever less than ShA rats on session 1 ^(p < .01). LgA rats showed less decay of active lever pressing than the ShA group *(p < .0001). Note that in all figure panels, presses on the active lever during the time-out period were not included.