Figure 2.

a, The mean ± SEM number of active and inactive nose pokes made by all rats during self-administration training sessions before group assignment, in which timeout intervals were gradually lengthened. b, The mean number of infusions made by all subjects during self-administration training sessions. During these training sessions, all rats received the cocaine infusion at the same speed (over 5 s), and the timeout intervals were increased each time a rat reached criterion performance for self-administration. Data presented in the 85 s timeout sessions are the average of all subjects comprising the “Baseline” data point presented in Figure 3.