Proverb comprehension impairments in schizophrenia are related to executive dysfunction

The study aimed to investigate the pattern of proverb comprehension impairment and its relationship to proverb familiarity and executive dysfunction in schizophrenia. To assess the specificity of the impairment pattern to schizophrenia, alcohol-dependent patients were included as a psychiatric comparison group, as deficits of executive function and theory of mind as well as dysfunction of the prefrontal cortex, which have been related to proverb comprehension difficulties, are common in both disorders. Twenty-four schizophrenia patients, 20 alcohol-dependent patients and 34 healthy controls were administered a multiple-choice proverb interpretation task incorporating ratings of subjective familiarity and measures of executive function. Schizophrenia patients chose the correct abstract and meaningful interpretations less frequently and instead chose the incorrect concrete (both meaningless and meaningful) proverb interpretations more often than alcohol-dependent patients and healthy controls. Relative to healthy controls, schizophrenia patients also chose more abstract-meaningless response alternatives and were impaired in all executive domains. Impaired divided attention was most consistently associated with proverb interpretation deficits in both patient groups. Taken together, schizophrenia patients showed a specific pattern of proverb comprehension impairments related to executive dysfunction and symptoms. The comparison with the alcohol-dependent subgroup suggests that a more comprehensive and severe impairment of complex higher-order cognitive functions including executive behavioural control and non-literal language comprehension might be associated with frontal dysfunction in schizophrenia as compared to alcohol use disorder.