Concurrent extinction of responding for cocaine and saccharin.

During extinction testing, the lever previously associated with cocaine was presented concurrently with the lever previously associated with saccharin during 45 min. Pressing on either lever was recorded but had no programmed consequence (no response-contingent reward delivery or light cue presentation). (A) Bars represent the mean total number of responses (± s.e.m.) on the cocaine- and saccharin-associated levers over the 45-min extinction period. *, different from the other reward (P<0.05, one-way ANOVA); (B) Curves represent within-session time course of extinction responding on the two levers (means ± s.e.m.). *, different from the other reward (P<0.01, Fisher's LSD test following a two-way ANOVA).