Frontal/executive impairments in schizophrenia

Abstract

A study of frontal/executive impairments in schizophrenia is reported. Schizophrenia patients and controls were not significantly different with respect to age, sex, and premorbid IQ. The schizophrenia group demonstrated significant impairments in cognitive flexibility and forward planning, replicating results from a 1990 study by Morice. Impairment prevalence figures of 65 and 76 percent for cognitive flexibility and forward planning, respectively, were demonstrated. Several tests for short-term memory were administered. Schizophrenia patients were not found to be impaired on tests of simple, or primary, short-term memory as measured by Digits Span Forward and Words Span Forward, but they were found to be significantly impaired compared with controls on two tests of working memory, Alphabet Span and Sentence Span. Using a cutoff derived from the mean score for the controls, 65 percent of schizophrenia patients proved to be impaired on Sentence Span. A total of 16 (94%) were impaired on one or more of the three tests of executive functioning used. The effects of IQ on test results were examined, and impairment of cognitive flexibility and forward planning seemed to occur regardless of whether premorbid IQ had been preserved or had deteriorated. However, working memory impairments occurred in the subgroup of schizophrenia patients demonstrating a substantial fall in IQ from premorbid levels. The ability to process increasingly complex information was addressed by a more detailed examination of the Tower of London results. There were no differences in performance between groups for the first three levels of complexity (1-3 moves), but significant, and increasing, differences emerged for the last three levels (4-6 moves). These results were taken to support the hypothesis that schizophrenia represents a loss of, or a failure to acquire, the ability to process complex information. Impairments of executive functions that could affect complex information processing could have implications for schizophrenia rehabilitation.