A major challenge in understanding any psychiatric disorder is knowledge of how the etiological factors that are operative in the illness unleash pathogenetic mechanisms that produce a pathological entity, a conserved set of molecular and cellular disturbances in the brain. This pathological entity then alters the normal circuitry and function of the brain, producing a characteristic pathophysiology that gives rise to the recognized clinical features of the disorder. In the case of schizophrenia, complex genetic factors are known to play a major role in the etiology of the illness. In addition, a number of epidemiological studies have demonstrated replicated associations between a range of environmental events, occurring from gestation through adolescence, and an elevated risk for the illness. Less common, however, are studies that address the intermediate processes between a given environmental exposure and the clinical illness that might point to the pathogenetic mechanisms linking etiology and pathology. Consequently, one of my favorite
Journal articles of 2009 is the study by Brown and colleagues
(6) that evaluated the relationship between serologically documented prenatal exposure to influenza or toxoplasmosis and cognitive function in individuals with schizophrenia. The authors found that patients who were exposed to infection in utero were more likely to have impaired performance on tasks that require cognitive set shifting. Although the neural substrate for this pattern of cognitive abnormalities was not evaluated, the results of this study help constrain the search for the types of pathogenetic mechanisms that might arise from prenatal infection and produce pathological alterations in the brain circuits that subserve cognitive set shifting.