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The relationship between a widely-used neuropsychological test of frontal lobe function, the Wisconsin Card Sort Test, and spatial working memory, as assessed by the oculomotor delayed response task, was examined in schizophrenic patients. Schizophrenic patients were impaired compared with bipolar and normal control subjects on both tasks and their working memory performance was significantly correlated with their WCST measures. The spatial working memory and the WCST deficits in schizophrenia may reflect disrupted circuitry mediated by the dorsolateral prefrontal system.
The aim of this study was to investigate dorsolateral prefrontal function, as assessed by a spatial working memory task, in relation to the syndromal features of schizotypal personality. We found a weak association between a self-report measure of schizotypy and the working memory performance. Those with a high score on the schizotypal personality questionnaire tended to make more errors on the spatial working memory task. One sub-scale of the schizotypal personality questionnaire that taps into social functioning was significantly correlated with working memory deficit. This result suggests the presence of subtle prefrontal deficit in a sub-group of psychometrically ascertained schizotypic individuals and renders support for the past reports of working memory deficit in schizophrenia and schizotypy.
It is known that the prestriate cortical regions that project to area LIP in parietal cortex and to areas TEO and TE in temporal cortex are mostly separated. Two separate streams of information transfer from occipital cortex can this be distinguished. We wished to determine whether the parietal and temporal streams remain segregated in their projections to frontal cortex. Paired injections of retrograde fluorescent tracers were placed in parietal and temporal cortex, or in the lateral and medial parts of the frontal eye field (FEF). The cortical regions containing retrogradely labeled cells were reconstructed in two-dimensional maps. The results show that temporal cortex mainly projects to lateral FEF (area 45). Parietal cortex sends projections to medial FEF (area 8a) and to lateral FEF, as well as to area 46. Thus, the parietal and temporal streams converge in lateral FEF. Most of the occipital regions projecting to medial FEF are the same as those projecting to parietal cortex, whereas lateral FEF receives afferents from the same occipital regions as those sending projections to temporal cortex. Thus, one can distinguish two interconnected networks. One is associated with the inferotemporal cortex and includes areas of the ventral bank and fundus of the superior temporal sulcus (STS), lateral FEF and ventral prestriate cortex. This network emphasizes central vision, small accades and form recognition. The other network is linked to cortex of the intraparietal sulcus. It consists of areas of the upper bank and fundus of STS, medial FEF and dorsal prestriate cortex. These areas encode peripheral visual field and are active during large saccades.
The authors attempted to replicate the study of Castro, Silbert, McNaughton, and Barnes (1989) in which it was concluded that bilateral saturation of hippocampal synaptic enhancement produced a deficit in acquisition of a spatial navigation problem in the Morris swim task. The original protocol was followed as closely as possible, but no effect of long-term enhancement (LTE) saturation on spatial performance in this task was found. This negative result suggests either that the previous finding using the swim task reflected statistical error or that some as yet undetermined variable is of critical importance in this phenomenon. The present negative finding also raises a question concerning the reproducibility of the earlier results of McNaughton, Barnes, Rao, Baldwin, and Rasmussen (1986) in which LTE saturation apparently led to a prolonged deficit on a different spatial task. Although negative results in such experiments do not constitute grounds for rejecting the underlying hypothesis, the present lack of a positive effect renders uncertain, for the time being, one of the lines of experimental support for the theory that LTE at hippocampal synapses reflects a mechanism for the associative, distributed storage of new spatial information.
With a delayed-response task, spatial working memory function was assessed in normal students who were selected for schizotypy. The Wisconsin Card Sorting Test was also administered. Twenty-eight undergraduate students who scored high on the Perceptual Aberration Scale (PerAb) and 23 who scored low on this scale participated in this study. High PerAb students performed less accurately compared with the low PerAb controls on the delayed-response task, and they were more than twice as likely as low PerAb students to be impaired. The groups did not differ in the number of perseverative errors or number of categories achieved on the Wisconsin Card Sorting Test, but, as predicted, high PerAb students were less able to maintain set than were the low PerAb students. Neuropsychological implications of these data are discussed.
BACKGROUND - Studies in nonhuman primates provide evidence that intact spatial working memory depends on the integrity of specific areas in the prefrontal cortex. Patients with schizophrenia have been shown to be impaired on spatial working memory tasks. Relatives of schizophrenic patients show a range of cognitive deficits in the absence of clinical symptoms (eg, thought disorder, eye tracking dysfunctions). We predicted that a significant proportion of relatives of schizophrenic patients would show deficits in working memory as measured by a delayed response task.
METHODS - In experiment 1, we tested 18 schizophrenic patients, 15 first-degree relatives of schizophrenic patients, and 18 normal control subjects on an oculomotor delayed response task. In experiment 2, we assessed the performance of another group of 12 first-degree relatives of schizophrenic patients and 16 different normal control subjects on a visual-manual delayed response task.
RESULTS - Relatives of schizophrenic patients showed significant deficits in working memory on both the oculomotor and visual-manual delayed response tasks.
CONCLUSIONS - Some relatives of schizophrenic patients are impaired on tasks that tap spatial working memory and that implicate the prefrontal system. The delayed response paradigm may be useful in elucidating the multidimensionality of the schizophrenic phenotype.