What kinds of cognitive dysfunction occur in patients with schizophrenia?
Studies over the last 15 years have clearly reawakened us to the idea that schizophrenia is a disorder of impairments in a variety of cognitive domains. This is not a new idea, as both Kraepelin and Bleuler focused on impairments in cognition as defining features of the illness. At present, it is clear that virtually every individual with schizophrenia is impaired cognitively. On average, individuals with schizophrenia score between 1 and 1.5 standard deviations below the mean on cognitive tests. Twin studies from Goldberg and colleagues2 have showed that in monozygotic twins discordant for the illness, the affected twin performs more poorly on cognitive tasks than the unaffected twin. A recent analysis by Keefe and colleagues3 demonstrated that virtually every individual with schizophrenia underperforms cognitively compared to predictions based on parental performance. Cognitive dysfunction is present during the prodromal and premorbid phases as well as at the first onset of psychosis
