Fig. 6.

Cumulative record showing the behavioral (lever press) response pattern for a single animal during the multiple schedule for water reinforcement and cocaine self-administration. The animal completed 23 responses for water (mean INT = 25.40 ± 1.59 sec), followed by a 20 sec time out period (indicated bydouble line in record). During the self-administration phase, the animal completed four responses in quick succession followed by an additional 14 regularly spaced responses (mean INT, 6.45 ± 0.51 min). The y-axis is the number of lever presses. Each upward deflection indicates a reinforced response (FR1). Note that the slope difference between this graph and Figure 1 is related to differences in the timebases (minutes vs seconds).