Fig. 1.
Nicotine infusions earned in the self-administration training sessions. The daily 1-h sessions were initiated with the illumination of a house light. Once the rats reached the FR requirement at the active lever, an IV nicotine infusion was delivered. Each nicotine infusion was paired with presentation of a compound visual stimulus (1-s lever light on followed by 20-s house light off). The number of nicotine infusions was presented as the mean. For the purpose of clarity, the standard error of means was not shown. *p<0.05; **p<0.001 different from Switched Lever group