The effects of atypical and conventional antipsychotics on reduced processing speed and psychomotor slowing in schizophrenia: A cross-sectional exploratory study

Abstract

Background: Psychomotor slowing is an intrinsic feature of schizophrenia, but little is known about its nature or to what extent it is influenced by antipsychotics. The Symbol-Digit Substitution Test (SDST) is an appropriate tool for assessing reduced processing speed, whereas performance on copying tasks may be more useful in evaluating psychomotor slowing. Objective: The primary aim of this study was to investigate the effects of different antipsychotic agents on psychomotor slowing in patients with schizophrenia. Methods: This cross-sectional study compared performance on line- and figure-copying tasks in schizophrenic inpatients (matched for symptomatology, demographic variables, and duration of illness) treated with risperidone, olanzapine, other atypical antipsychotics (amisulpride, aripiprazole, clozapine, or quetiapine), or conventional antipsychotics (bromperidol, flupentixol, haloperidol, pimozide, or zuclopenthixol) and in healthy controls. Other tests administered included the SDST to assess processing speed, the California Verbal Learning Test to gauge verbal memory, the Letter-Number Sequencing task to assess working memory, and the Wisconsin Card Sorting Test to measure executive function. Comparisons were made between each patient group and healthy controls; between patient groups; and, post hoc, between atypical and conventional antipsychotics. Results: The study included 26 patients treated with risperidone, 24 treated with olanzapine, 25 treated with other atypical antipsychotics, 21 treated with conventional antipsychotics, and 25 healthy controls. The groups were well matched in terms of sex, educational level, mean doses, and duration of illness. The conventional-antipsychotic group was significantly older (P = 0.026) and had significantly higher positive symptoms scores (P = 0.031) on the Positive and Negative Syndrome Scale compared with the risperidone group. Patients treated with conventional antipsychotics had significantly greater slowing on the copying tasks compared with patients treated with atypical antipsychotics (P ≤ 0.050 for 3 of 4 measures generated by the copying tasks). No significant differences were found on the classic neuropsychological tasks. All patient groups had poorer performance on the psychomotor measures compared with controls. No significant differences were found between the groups receiving atypical antipsychotics. Conclusion: Based on performance on the line- and figure-copying tasks, atypical and conventional antipsychotics appeared to have differential effects on psychomotor slowing in these schizophrenic inpatients.