Figure 1.

Cocaine infusions received for all limited-access and extended-access groups during each day of cocaine self-administration. No significant differences occurred in the number of daily infusions received either between limited-access groups or between extended-access groups. The number of cocaine infusions received by all extended-access rats during self-administration sessions 7–11 was significantly higher than that for session 1 (*p < 0.05; **p < 0.0001); no significant differences were reported between self-administration sessions in limited-access rats. Error bars indicate SEM. N, number of animals for each group.