Multiple Memory Systems in People With Schizophrenia: Possible Effect of Atypical Anti-Psychotic Medications
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Patients with schizophrenia are normally treated with one of several antipsychotic medications that differ from one another in the areas of the brain they affect including the dorsal striatum, a subcortical section of the forebrain, and the prefrontal cortex (PFC), located in the anterior part of the frontal lobes. Two different tests of implicit memory, the probabilistic classification learning (PCL) and the Iowa gambling task (IGT), have been shown to rely on the dorsal striatum and the PFC, respectively. Studies have previously shown that patients with schizophrenia treated with antipsychotics that affect the dorsal striatum (e.g., risperidone), have altered performance on the PCL, and those treated with antipsychotics that affect the PFC (e.g., clozapine), have altered performance on the IGT. We tested the hypothesis that patients with schizophrenia treated with olanzapine would have a poorer performance on the IGT, but not the PCL, when compared with controls. This study aimed to clarify conflicting results from prior experiments observing the effects of olanzapine on implicit memory in people with schizophrenia. We also hypothesized that performance of patients taking aripiprazole would be comparable to those taking risperidone, or an FGA; however, we were unable to recruit a sufficient amount of participants to test this hypothesis. Patients with schizophrenia, a mental disorder characterized by a breakdown in relation between thoughts, emotion, and behavior, treated with olanzapine were recruited through local psychiatric clinics or using a newspaper ad. Administration of the Brief Psychiatric Rating Scale (BPRS) and the Mini Mental State Examination (MMSE) preceded a brief questionnaire of demographic information. Participants were tested on the PCL and the IGT using a personal computer. Results revealed poorer performance on both the MMSE and BPRS for patients when compared with controls. Patients taking olanzapine were impaired in learning the PCL but not the IGT when compared with controls. Results suggest that olanzapine acts on the PFC to augment IGT performance but further studies are needed.