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

(A) Mean (±SEM) number of active and inactive lever presses for females and males across the 1-h sessions during the Experiment 1 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 < .001). There was a significant difference between active and inactive lever pressing on session 1 for males only +(p < .05). (B) Mean (±SEM) number of active lever presses for ShA and LgA females and males across sessions during the Experiment 1 escalation. LgA rats pressed the active lever more on session 1 than ShA rats #(p < .0001). LgA rats escalated intake across sessions *(p < .0001), 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 1 escalation. 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 the Experiment 1 extinction. LgA rats pressed the active lever less than ShA rats on session 1 ^(p ≤ .05). LgA rats showed less decay of active lever pressing than ShA rats *(p < .001). Note that in all figure panels, presses on the active lever during the time-out period were not included.