Do neuroleptics impair learning in schizophrenic patients?

Dopamine (DA) has been shown to be involved in reward-related (incentive) learning but not stimulus-stimulus (s-s) associative learning. Schizophrenic individuals receive neuroleptics (DA receptor blockers) for therapy and therefore may have impaired incentive learning. To test this hypothesis, in experiment 1, schizophrenic outpatients receiving haloperidol or flupenthixol and matched controls were tested on tasks involving incentive or s-s learning. Patients were also given the Brief Psychiatric Rating Scale (BPRS). Results showed the patients to be significantly impaired in every task. However, only impairments of s-s learning were correlated with psychiatric state. Thus, deficits on the tasks involving incentive learning were interpreted as resulting from neuroleptic drugs rather than psychiatric state. Experiment 2 tested 26 schizophrenic inpatients receiving a variety of neuroleptics (converted to chloropromazine equivalency (CPZEQ)) on the same tasks. A blood sample was collected from the patients and from age-matched controls and prolactin levels were found to be significantly higher in the patients. Multiple regression analysis was used on patient data to determine whether prolactin level or CPZEQ were related to performance. It was found that incentive learning but not s-s associative learning was significantly predicted by one of these two indexes of neuroleptic drug dose. The results of these experiments provide some support for the hypothesis that neuroleptics might impair incentive but not s-s associative learning in schizophrenics. The observation that neuroleptics affect human incentive learning might lead to more efficient use of behavior modification programs in the treatment of schizophrenia.