Fig. 1

Mean (± SEM) cocaine infusions (0.4 mg/kg) are presented for each day of the extended access phase (6 hr) and for the last day of the short-access (ShA) condition (2 hr) before extended access (left unconnected points) and the first day of ShA after extended access (right, unconnected points). The inset represents mean cocaine infusions earned during the first 2 hr of extended access. Horizontal lines indicate the 3-day intervals during which there were significant group differences in responses or drug deliveries (ps < 0.05). During interval 1 (days 1-3) LoI rats earned more cocaine infusions than HiI rats (ps < 0.05). During interval 7 (days 19-21) the HiI group earned more infusions than the LoI group (ps < 0.05). HiI (vs LoI) rats also earned more infusions during interval 6 (days 15-18). * = p < 0.05 block 1 < blocks 3-7 in the HiI group. † = p < 0.05 ShA before vs. after extended access in the HiI group and HiI > LoI in ShA infusions after extended access (p < 0.05).