Season of birth and neuropsychological impairment in schizophrenia.

Repeated studies suggest a relationship between winter birth and increased incidence of schizophrenia. Furthermore, there may be seasonal fluctuations in schizophrenia risk factors (e.g., influenza epidemics) and the severity of biological anomalies (e.g., enlarged cerebral ventricles in neuroimaging studies). In order to assess whether winter-born schizophrenics show greater neuropsychological impairment, 112 males meeting Research Diagnostic criteria for schizophrenia were administered the Luria-Nebraska Neuropsychological Battery, a thorough measure of higher cortical functioning deficit. Sixty-four of these 112 patients were also administered the Wechsler Adult Intelligence Scale-Revised, the Benton Visual Retention Test, and the Rey Auditory Verbal Learning Test. Despite the use of several definitions of winter and nonwinter birth, there was no evidence of elevated rates of neuropsychological dysfunction among winter-born patients on any measure. The current study contains certain limitations (e.g., variable medication status at testing), but the results suggest no strong season of birth relationship with neuropsychological impairment in a reasonably large, research-diagnosed sample of schizophrenic patients.