Figure 1. A longer drug-free period results in greater drug-seeking following cocaine self-administration.

(a) Schematic of behavioral training timeline. (b) After 7 days of traditional FR1 cocaine self-administration, rats were trained for an 7 additional days on a modified FR1 paradigm that introduced discrete trials. The start of each trial was signaled by extension of the levers into the chamber, and rats could make 1 of 3 responses: active lever press, inactive lever press, or omission. Active lever presses resulted in cocaine infusion, CS presentation, and lever retraction. Inactive lever presses resulted in lever retraction and a variable inter-trial-interval (ITI). Omissions occurred if a rat made no response for 30s, and resulted in lever retraction and a variable ITI. The drug-seeking test was performed using the same discrete trials paradigm, but no cocaine (only CS) was delivered in response to an active lever press. (c) Over 14 days of cocaine self-administration, rats in both groups (D1: n=15; D15: n=18) self-administered a similar number of cocaine infusions (mean ± sem; main effect of D1/D15 group: F_(1,403) =1.89, p=0.18) (d) Incubation of cocaine craving. Rats that experienced a 15-day drug-free period (D15) made more active lever presses (mean ± sem) and had faster response latencies during the drug-seeking test (median, box represents 25^th and 75^th percentiles, bars represent minimum and maximum values). *p<0.05, two-tailed t-test.