FRONTAL-STRIATAL COGNITIVE DEFICITS IN PATIENTS WITH CHRONIC-SCHIZOPHRENIA

Spatial working memory and planning abilities were assessed in 36 hosp italized patients with chronic schizophrenia, using the computerized C ambridge Neuropsychological Test Automated Battery (CANTAB), and compa red with those of normal subjects and patients with neurological disor ders (frontal lobe lesions; temporal lobe and amygdalo-hippocampal les ions; Parkinson's disease), matched for age, sex and National Adult Re ading Test IQ. The patients in the group with temporal lobe lesions we re unimpaired in their performance on these tasks. Patients with schiz ophrenia were impaired on visuo-spatial memory span compared with all the other groups, while severity of Parkinson's disease was correlated with the degree of impairment on this task. The patients with schizop hrenia and those with frontal lobe lesions were impaired on a 'spatial working memory' task, with increased 'between-search errors'. Patient s with Parkinson's disease performed this task poorly compared with th e younger control subjects. Patients with schizophrenia were unable to develop a systematic strategy to complete this task, relying instead on a limited visuo-spatial memory span. Higher level planning ability was investigated using the CANTAB 'Tower of London'. All groups were e qually able to complete the task. However; the groups of patients with schizophrenia and frontal lobe lesions made fewer perfect solutions a nd required more moves for completion. Movement times were significant ly slower in the schizophrenia group, suggesting impairment in the sen sorimotor requirements of the task. The patients with schizophrenia we re not impaired in their 'initial thinking' (planning) latencies, but had significantly prolonged 'subsequent thinking' (execution) latencie s. This pattern resembled that of the group with frontal lobe lesions and contrasted with the prolonged 'initial thinking' time seen in Park inson's disease. The results of this study are indicative of an overal l deficit of executive functioning in schizophrenia, even greater than that seen in patients with frontal lobe lesions. However the pattern of results in schizophrenia resembled that seen in patients with lesio ns of the frontal lobe or with basal ganglia dysfunction, providing su pport for the notion of a disturbance of frontostriatal circuits in sc hizophrenia. Our findings also indicate that there is a loss of the no rmal relationships between different domains of executive function in schizophrenia, with implications for impaired functional connectivity between different regions of the neocortex.