Anomalous cerebral asymmetry and language processing in schizophrenia

Reversal or reduction of normal structural cerebral asymmetries may be related to the pathogenesis of schizophrenia, but this relationship remains controversial. We review the literature and describe a further study designed to detect whether anomalous asymmetries are present early in the illness (at the first episode), whether they predict deficits in language processing, and whether they may be related to a genetic predisposition for schizophrenia. Asymmetries of brain widths and segments of the sylvian fissure were assessed in a magnetic resonance imaging study of 87 patients with a first episode of schizophrenia and 52 normal controls. These asymmetries were correlated with specific measures of language processing, memory, and hand skill. An independent group of 14 pairs of siblings with schizophrenia were also evaluated for evidence of heritability to cerebral asymmetries. Width asymmetries were reduced in patients compared with controls in the posterior (p = 0.02) and occipital (p = 0.05) regions. Brain horizontal length, on the other hand, was significantly more asymmetrical in patients (left > right; p = 0.04). For sylvian fissure measurements, asymmetries in controls (left > right) were greatest for the horizontal component; this asymmetry tended to detect differences in patients by comparison with controls (p < 0.06). In a range of tests of language and memory, few significant correlations between performance and cerebral asymmetries were detected either in patients or controls, although patients consistently scored poorer than controls in the majority of tests. In 14 pairs of psychotic siblings, within-pair correlations for the horizontal sylvian fissure asymmetry were significantly greater than between-pair correlations. These findings are consistent with the early presence (possibly genetic) of anomalous cerebral asymmetry. However, the functional correlates of reduced asymmetry remain obscure.