Figure 1.

Changes in motivation for cocaine and food pellets over the course of self-administration. (a) Cocaine BP. (b) Pellet BP. Time blocks that do not share a letter are different from one another within a give preference group (p<0.05). The far right section in each panel represents the same data from the 25 CP rats segregated by whether individuals were still ‘pellet preferring' (open circles, ‘before CP') or were displaying cocaine preferences (closed circles, ‘after CP') at each time. The numbers associated with each point represent the number of CP individuals in each subgroup in each given week. Significant difference from PP (*p<0.05) and ABST rats (^#p<0.05). Vertical lines represent SEM. ABST, abstaining; BP, breaking point; CP, cocaine preferring.