Impairments in a variety of cognitive functions are found in patients with schizophrenia. These impairments affect a wide array of different cognitive abilities and are often quite severe, when compared to standards based on healthy individuals of the same age, education levels, and gender. Cognitive impairments appear to be present across the lifespan, detectable at the time of the first treatment episode, if not before, and to manifest a generally stable course over time. Although the current knowledge base regarding cognition in schizophrenia is quite broad, additional research information is constantly accruing. The main purpose of this chapter is to provide a broad overview of the domains, severity, and course of cognitive impairments in schizophrenia, with a focus on functional relevance and treatment possibilities.

Cognitive impairments were reported by both Emil Kraepelin and Eugen Bleuer, both of whom noted that they believed that cognitive impairments were amongst the core features of the illness. The conception of dementia praecox introduced by Kraepelin focused on the cognitive and functional deficits in the illness and likened the condition to a condition such as Alzheimer’s disease with an earlier onset age. Over the first half of the twentieth century research on cognition in schizophrenia focused on a variety of different topics, including memory, attention, and language skills.⁽¹⁾

The development of clinical neuropsychology and formalized neuropsychological (NP) tests led to a substantial increase in interest in cognition in schizophrenia. Classical NP ability domains, as well as the types of tests typically used to assess them are presented in Table 4.3.3.1. Clinical NP assessments develop an understanding of areas of relative strength and weakness, comparing current functioning following illness or injury to evidence or estimates regarding prior functioning.⁽²⁾ Then a profile can be developed, contrasting better or more poorly performed ability areas. Performance across these ability areas can be converted to standard scores, considering demographic factors that influence performance such as age, education level, and sex.⁽³⁾ Thus, the results of a clinical NP assessment provide a summary of relative strengths and weaknesses. Clinical NP assessment has moved away from earlier efforts to anatomically localize deficits through test performance or to distinguish ‘functional’ versus ‘organic’ impairments. The current conception of neuropsychological performance is largely based on the concept of functional neural networks, which link cortical and subcortical regions through patterns of linked activation during task performance.⁽⁴⁾