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OBJECTIVE: It has been suggested that in healthy persons higher-order cognitive processing engaged by incremental working memory load hierarchically employs more dorsal than ventral prefrontal resources in healthy individuals. Given that working memory performance is impaired in schizophrenia, especially at higher executive loads, the authors investigated how this prefrontal functional organization might be altered in disease, independent of performance deficits. METHOD: Using N-back working memory functional magnetic resonance imaging (fMRI) data, the authors studied 15 patients with schizophrenia and 26 healthy comparison subjects. Subgroups based on median performance accuracy at 2-back were analyzed; high performers included eight schizophrenia patients and 14 comparison subjects, and low performers included seven patients and 12 comparison subjects. RESULTS: High-performing but not low-performing comparison subjects responded to incremental working memory executive load with disproportionately greater dorsal but not ventral prefrontal cortex activation, which also predicted performance accuracy. In the high- and low-performing patient groups, incremental working memory load caused a disproportionate increase in ventral but not dorsal prefrontal cortex activation relative to the respective comparison group, which also correlated with accuracy. Functional connectivity between the ventral prefrontal cortex and posterior parietal cortex was relatively greater in patients, whereas comparison subjects had greater functional connectivity between the dorsal prefrontal cortex and posterior parietal cortex. CONCLUSIONS: The hierarchical organization of the prefrontal cortex may be compromised in schizophrenia, resulting in loss of functional specialization and integration at the dorsal prefrontal cortex and in compensatory activation from the ventral prefrontal cortex, which may ultimately affect working memory and executive cognition. [ABSTRACT FROM AUTHOR]

OBJECTIVE: Prefrontal dysfunction is considered a fundamental characteristic of schizophrenia. Recent electrophysiological evidence points to a major instability of signal processing in prefrontal cortical microcircuits because of reduced phase-synchronization (i.e., an increased stimulus-related variability [noise] of single-trial responses in the spatial and time domain). The authors used functional magnetic resonance imaging (fMRI) during a visual two-choice reaction task in order to measure, with higher topographic accuracy, signal stability in patients with schizophrenia and its relationship to more traditional measures of activation. METHOD: Twelve clinically stable inpatients with schizophrenia and 16 matched comparison subjects were evaluated. Event-related blood-oxygen-level-dependent responses were subjected to an analysis of residual noise variance and to independent data dimension independent component analysis in the medial prefrontal cortex. RESULTS: In patients with schizophrenia, the authors found increased residual noise variance of the blood-oxygen-level-dependent response that predicted the level of prefrontal activation in these subjects. In the left hemisphere, residual noise variance strongly correlated with psychotic symptoms. Independent component analysis revealed a 'fractionized' and unfocussed pattern of activation in patients. CONCLUSIONS: These findings suggest that unstable cortical signal processing underlies classic abnormal cortical activation patterns as well as psychosis in schizophrenia. [ABSTRACT FROM AUTHOR]

OBJECTIVE: Impaired attention has frequently been observed in studies of unaffected siblings of patients with schizophrenia. To assess the suitability of impaired attention for use as an intermediate phenotype in genetic studies, the authors estimated the relative risk of impaired attention in a large group of siblings. METHOD: The authors used the Continuous Performance Test, 1-9 version, with and without a distraction condition, to study 147 patients with schizophrenia, 193 of their siblings, and 47 normal comparison subjects. Relative risk (l) was estimated by using cutoff scores that were one, two, and three standard deviations below the mean sensitivity index value (d cent) of the normal comparison group in both Continuous Performance Test conditions. RESULTS: Patients but not their siblings performed worse than the normal comparison subjects in both conditions. Fifty percent of the patients, 24% of their siblings, and 18% of the normal comparison subjects scored one standard deviation below the mean score of the comparison group for the more difficult distraction version of the Continuous Performance Test. The patients with Continuous Performance Test scores one standard deviation below the mean score of the comparison group had a total of 97 siblings. Compared with the comparison group, this subgroup of siblings had significantly lower Continuous Performance Test scores. Relative risk was also significantly higher for the siblings of patients whose scores were one standard deviation (l=2. 1) and two standard deviations (l=3.3) below the mean of comparison subjects. Attempts to assess ascertainment bias suggest that this may be an underestimate. CONCLUSIONS: Poor performance on the Continuous Performance Test appears to be familial and, possibly, genetic. Relative risk estimates were in the moderate range. Given the ease of administering the Continuous Performance Test, the use of impaired attention as an intermediate phenotype could increase the power of genetic studies of schizophrenia. [ABSTRACT FROM AUTHOR]

Objective: This study was carried out to confirm prior evidence of an effect of a single nucleotide polymorphism (SNP) in the metabotropic glutamate receptor 3 (GRM3) gene (a putative risk factor for schizophrenia) on measures of N-acetylaspartate in healthy comparison subjects.Method: Fifty-four carefully screened healthy volunteers genotyped at SNP rs6465084 underwent magnetic resonance spectroscopic imaging (MRSI) at 3 T and selected neuropsychological testing.Results: The A/A genotype group exhibited a significant reduction of N-acetylaspartate/creatine levels in the right dorsolateral prefrontal cortex compared to the G carriers. A tendency in the same direction was seen in the left dorsolateral prefrontal cortex and in the white matter adjacent to the prefrontal cortex.Conclusions: These findings provide further evidence that GRM3 affects prefrontal function and that variation in GRM3, monitored by SNP rs6465084, affects GRM3 function. [ABSTRACT FROM AUTHOR]