Knowledge of the relationship between specific cognitive abnormalities and the clinical symptoms of schizophrenia could give insight into the nature of their underlying pathophysiology. Composite scores were generated for negative, disorganized, and psychotic symptom ratings in 134 patients with schizophrenia (DSM-IV criteria). Partial correlations (each composite corrected for the others) were computed with neuropsychological measures. Negative symptoms were related to poor performance on tests of verbal learning and memory, verbal fluency, visual memory, and visual-motor sequencing. Disorganized symptoms were correlated with lower verbal IQ and poor concept attainment. Psychotic symptoms had no significant relationship with cognitive deficit.

The abnormal task-related rCBF asymmetry in STG of schizophrenic patients may indicate an isolated temporal lobe deficit, but it may also indicate abnormality in the thalamocortical circuitry mediating selective attention and/or in the brain systems that integrate auditory processing in the 2 hemispheres.

Brain mechanisms involved in the maintenance of attention to auditory and visual stimuli at different spatial locations were assessed using positron emission tomography with [15O]water to measure regional cerebral blood flow (rCBF) changes in 13 normal volunteers. Simultaneous auditory [dichotically presented consonant-vowel-consonants (CVCs)] and visual stimuli (vertically oriented, CVCs presented to the left and right of fixation) were presented on every trial. In different conditions subjects attended for targets in a specified stimulus channel (left or right ears or left or right visual fields) while maintaining fixation on a central x. Attending left or right for auditory stimuli increased rCBF in primary auditory cortex in Heschl's gyrus and in temporal lobe auditory association cortices in both hemispheres. Attending left or right for visual stimuli did not change rCBF in primary visual cortex, and only attention to the right significantly increased rCBF in contralateral occipital cortex. Visual attention caused significant rCBF changes in a widespread network that included frontal, parietal, and temporal cortical regions as well as the cerebellum, whereas rCBF changes due to auditory attention were largely localized in the temporal lobes. The results suggest that spatially directed attention is mediated by different mechanisms in the auditory and visual modalities.

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