Fig. 1.

Experimental timeline. Following a baseline period during which cocaine self-administration was only available during daily 2-h cocaine vs food choice sessions (0900–1100 h), monkeys were subsequently provided access to cocaine during both choice sessions and daily 20-h extended access sessions (1200–0800 h). During extended-access sessions, 0.1 mg/kg/injection cocaine was available under a FR 10/time out 15-min schedule of reinforcement. (A) After 14 days of extended cocaine access, 0.032 mg/kg/h d-amphetamine was continuously infused for 7 days, and then the dose was increased to 0.1 mg/kg/h d-amphetamine for 14 days for a total of 21 consecutive d-amphetamine treatment days. (B) After 14 days of extended cocaine access, 0.001 mg/kg/h risperidone was continuously infused for 7 days, then 0.0032 mg/kg/h for 7 days, and then 0.0056 mg/kg/h for 7 days for a total of 21 consecutive risperidone treatment days.