Figure 1.

Experimental progression. The study used a within-subjects design (N=24) with 5 distinct experimental phases as outlined in the above figure (refer to black filled rounded rectangles). The first phase assessed individual demand for sucrose. The second phase modeled drug taking and assessed individual demand for nicotine (doses for all treatments can be found in the figure). The third phase assessed the effects of acute bupropion or varenicline pretreatment on responding for nicotine. The fourth extinction phase modeled abstinence. The fifth phase modeled relapse and in this phase resurgence of active lever responding in extinction was triggered by non-contingent presentation of cues that were previously paired with nicotine infusions, nicotine, bupropion, or varenicline.