To master the odor-driven stimulus discrimination task, D2R-/- mice required significantly more trials (Fig. 3A: t(14) = 2.20; p < 0.05) and committed more errors (Fig. 3B: t(14) = 2.92; p < 0.05) than D2R+/+ mice to learn to associate a specific odor with the presence or absence of the food reinforcer. However, both genotypes did learn the task and eventually maintained accurate discrimination for a minimum of 8 correct responses out of 10 trials.