Comparison of set-shifting ability in patients with chronic schizophrenia and frontal lobe damage

Neuropsychological studies of patients with schizophrenia have consistently identified deficits on tests sensitive to frontal lobe function. One parad igm that has been widely used is that of attentional set-shifting using the Wisconsin Card Sorting Test (WCST). In the present study, patients with ch ronic schizophrenia and with frontal lobe lesions were assessed on a comput erised set-shifting task that provides a componential analysis of the WCST by distinguishing between intra-dimensional and extra-dimensional set-shift ing. Out of 51 patients with schizophrenia, those with high IQ (n=24) were compared with patients with lesions in prefrontal cortex (n=22) and with no rmal control subjects (n=18). These three groups were well matched for age, sex and National Adult Reading Test (NART) IQ. The schizophrenic group sho wed a significantly higher rate of attrition at the intra-dimensional shift stage of learning compared with the other two groups. At the extra-dimensi onal shift stage, both the schizophrenic and frontal lesioned groups showed greater attrition than controls. Further, patients with schizophrenia who were able to learn the intradimensional reversal stage required more trials and made significantly more errors at that stage than the other two groups . In comparison with high IQ patients with schizophrenia, those with low IQ performed at a lower level but showed a qualitatively similar pattern of p erformance, providing further evidence that the set-shifting deficits were not simply explained by any global intellectual decline. Patients with schi zophrenia who dropped out at the extra-dimensional shift stage had higher n egative symptom scores compared with patients dropping out at previous lear ning stages, while patients failing at the intra-dimensional shift stage ha d lower scores for bradyphrenia (slowness of thought). The results suggest that patients with chronic schizophrenia fail to 'learn set' and are impair ed at both set-shifting and concept formation. The relevance of these findi ngs to understanding the nature of prefrontal cortical deficits in chronic schizophrenia is discussed. The implication of these findings to the rehabi litation of these patients is considered. (C) 1999 Elsevier Science B.V. Al l rights reserved.