The hypothesis of the presence of cognitive dysfunction in people with schizophrenia dates back to the constitution of modern psychiatry, when Kraepelin conceptualized the disorder as dementia praecox. This theory has received limited credit for a long time, although the clinicians have continued to recognize that in people with mental retardation there is an increased vulnerability (psychosis of engagement). Only in the last twenty years, on the basis of the progressive affirmation of pathogenic models pertaining to neurodevelopment, identification and treatment of cognitive deficits has been a subject of renewed interest.
Cognitive deficits affect the mass majority of schizophrenia patients, with prevalence estimates that averaged about 75-80% of the patient population and a quantification that was between 1 to 2 standard deviations below the mean of the average population. A meta-analysis conducted by Heinrichs and Zakzanis of 204 studies comparing a total of 7,420 patients with schizophrenia and 5,865 healthy controls showed a deterioration of global cognitive functioning with a very significant effect size. Systematic reviews more recently have shown a similar deterioration in people with the first episode of the illness, in those never treated with antipsychotic drugs or those in remission of symptoms.
The cognitive impairments that are most frequently encountered are:
1. Reduction of intelligence quotient (IQ), already observed in children who later develop the disease and more clearly with the onset of the disorder, to be able to present a substantially stable course;
2. Attention deficits, in particular the responsiveness to sensory stimuli;
3. Deficits in working memory;
4. Deficits in verbal memory, immediate and delayed;
5. Deficits in executive functioning, with particular difficulty in categorizing information and errors in preservation.
People with intellectual disabilities are affected with schizophrenia more often than the general population. The recent epidemiological data shows an incidence of about 3-5.2% versus 0.7. For people with intellectual disabilities, the changes of form and content may be difficult to assess, especially in those cases where the expressive-communicative dimension pertains exclusively to the behavior. The translation of psychiatric symptoms at the observational-behavioral level is one of the areas of research for CREA. The center has recently completed the validation of a new assessment tool called SPAID-G and is refining a whole battery for all of the more frequent psychopathological areas.
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This article has been translated and adapted to English (American) by Julie Colangelo