Figure 2.

Effects of l-amphetamine on total number of lever presses (correct plus incorrect) by SHR and WKY controls. Means ± SEM. Sessions 31 through 44 served as baseline sessions. Treatment was given at sessions 45 through 58. Sessions 59 through 61 were used for studying post-treatment effects, except for the groups that received vehicle (saline, 0 mg/kg) during treatment sessions 45-58. These groups received 2.2 mg/kg l-amphetamine to check for typical responsiveness to the drug for SHR and WKY.