Cognitive deficits in schizophrenia; Cognitive disturbances of schizophrenia Definition Patients with schizophrenia exhibit about a 1-2.5SD decline in a range of cognitive domains, e.g., several types of memory, executive function, verbal fluency, and attention/information processing. The cognitive impairment is measured by neuropsychological tests. Backgrounds The concept of cognitive impairment in schizophrenia (CIS) can be traced back to "dementia praecox" coined for the illness by E. Kraepelin. Also, it is noteworthy that E. Bleuler, who assumed the change of brain function in schizophrenia, included disturbances (loosening) of association in the core symptoms of the disease. More recently, these traditional views regarding CIS have been quantified by objective measures, mainly neuropsychological tests. Several cognitive domains profoundly impaired ("differential deficits") in schizophrenia include verbal memory, executive function, verbal (category) fluency, and attention, as indicated by meta-analytic studies (e.g., Reichenberg and Harvey 2007). Assessments Some internationally standard neurocognitive test batteries covering key cognitive domains have been developed for the assessment of therapeutic effects. These include MATRICS Consensus Cognitive Battery (MCCB) (Nuechterlein and Green 2006), the CogState Schizophrenia Battery, and the Brief Assessment of Cognition in Schizophrenia (BACS) (Harvey 2013). Figure 1 demonstrates the scores of the MCCB Japanese version in patients with schizophrenia, showing impaired performance on tests of information processing/speed, attention/vigilance, working memory, verbal learning, visual learning, reasoning/problem solving, and social cognition.