It seems that the reinforcing effect of corn oil in the operant task is mediated through D2 receptors in the operant task. This discrepancy between the CPP test and the operant test comes from the detecting system in the test. Recent studies suggest that D1 receptors in particular contribute to the instrumental and the reward-related incentive learning process (Kelley et al., 1997; Dalley et al., 2005). D1 antagonists might affect the learning process in the CPP test, since subjects were …
