Cognitive impairments in schizophrenia are present before the onset of psychosis, possibly starting during puberty. Although there might be some worsening around the time of the first episode, the deficits plateau after the initial episode and probably remain stable throughout life. In other words, the cognitive damage is done once patients present with psychosis.

Even those patients who are unimpaired on testing around the time of their first episode of psychosis probably have an illness-related decrement in their cognitive function. In one study, patients performed on average about 15 points lower on the IQ scale than expected.

On neuropsychologic testing, the pattern of impairment is described as both generalized (performance is impaired on a wide variety of tests) and specific (there is a typical pattern of impairment, with some areas more impaired than others) (Bilder et al., 2000). The biggest impairments are seen in the areas of attention (such as sustained attention or vigilance), verbal learning and memory, and executive function. In these key areas of cognition, patients show impairments between 1 and 1½ and 2 standard deviations below healthy controls. Social cognition, reasoning and problem solving, and speed of information processing are other cognitive domains that are usually measurably impaired.

A simplified neuroanatomical model of cognition in schizophrenia suggests that almost all patients have some problems with basic memory and learning (temporal-hippocampal system), coupled with executive dysfunction (prefrontal systems). The prefrontal dysfunction, in particular, prevents the use of organizational strategies to learn new material, which is necessary for effective learning. In Alzheimer disease, the memory problem is rather basic (the memory stores themselves are degraded); in schizophrenia, some aspects of the memory problem are at a higher level (where strategies and flexibility are needed for better access of memory stores). The cognitive problems of schizophrenia are unlike those of Alzheimer dementia or of typical “brain damage” in that the disease is neither progressive nor can the dysfunction be easily localized to one particular brain area, respectively. It is therefore better to think of impaired function (e.g., executive dysfunction) as opposed to impaired regions (e.g., frontal lobe dysfunction).