| The goal of this project was to determine whether schizophrenic patients show deficits in delayed-response tasks (DRT) which have been found to be impaired in prefrontal pathology. Deficits in working memory for spatial location, assessed by DRTs, is a major symptom displayed by monkeys with lesions in the dorsolateral prefrontal cortex (DLPFC) (e.g. Goldman-Rakic, 1987). This deficit implicates the role of prefrontal cortex in representational memory necessary for context-relevant response selection. In addition, the possibility was tested that the Smooth Pursuit Eye Movement (SPEM) Dysfunction which is displayed by about 65-80% of all schizophrenics may be related to the disorders of the prefrontal cortex.; 12 schizophrenics, 12 psychiatric controls (bipolar affective disorder) and 12 normal controls, matched in age, years of education, IQ and socioeconomic status participated in 4 experiments. These were (1) Oculomotor DRT, (2) Haptic DRT, (3) Smooth Pursuit Eye Tracking Task, and (4) neuropsychological tests of frontal lobe functions. The two DRTs assessed prefrontal functioning in two modalities: oculomotor and haptic. In addition a verbal working memory task was administered to test the hypothesis that the working memory deficit is not general but restricted to the spatial domain. The performance on the DRTs was compared with that on the SPEM task and the neuropsychological tests of frontal lobe functions. Two tests of the frontal lobe were used: the Wisconsin Card Sort Task (WCST) for dorsolateral prefrontal function and Verbal Fluency Task (FAS) for medial/orbital frontal functions.; Schizophrenics were impaired compared to the other two control groups, in both oculomotor and haptic DRTs but the verbal working memory was intact in schizophrenics. In addition, schizophrenics were very much impaired on WCST but not on FAS, and their scores on the DRTs were highly correlated with the WCST but not with the FAS. This pattern implies that the problem lies in the dorsolateral prefrontal cortex and not in the medial/orbital frontal area. However, schizophrenics were not statistically more impaired on SPEM compared with the normals. Hence, the relationship between the prefrontal dysfunction and SPEM dysfunction is not clear, but it merits further investigation. |
