Differential effects of D₂- and D₄-blocking neuroleptics on the procedural learning of schizophrenic patients

Objective: To illustrate the differential effects of D₂- and D₄-blocking neuroleptics on the procedural learning of patients with schizophrenia. Method: Twenty-nine schizophrenic patients were divided into 3 groups according to their pharmacological treatment: 1) drug-naive, 2) haloperidol, and 3) clozapine. They were all assessed on clinical and procedural measures, the latter being the mirror drawing task. Results: All groups showed progressive learning over the successive trials, and drug-naive patients performed better than the other groups. Patients in the haloperidol group showed many fluctuations over trials, suggesting difficulty in the progressive automation of the task. Such fluctuations did not occur in the clozapine group, but performances per se were worse than in the other groups during the learning trials. Automation of the task occurred at the same point (second block of trials) for all groups. Conclusion: These results suggest that D₂- and D₄ blocking neuroleptics do not similarly affect striatal dependent procedural learning in schizophrenia.