Thought disorder in schizophrenia is associated with both executive dysfunction and circumscribed impairments in semantic function

Abstract

BACKGROUND: Formal thought disorder (FTD) has long been regarded as a key sign of schizophrenia but little is known about its origins or aetiology. One suggestion is that it is directly related to disordered language functioning; a second is that it is a reflection of poor neurocognitive functioning. A current model posits that it is related to a combination of executive dysfunction and impaired semantic processing. METHOD: To examine these alternative ideas, a heterogeneous group of 30 patients, all carrying a diagnosis of schizophrenia, and 18 non-patient controls completed a series of neurocognitive and psycholinguistic tests, and a clinical review that, inter alia, permitted assessment of thought disorder (TD) using the Thought, Language and Communication Scale (TLC). RESULTS: Patients generally performed at a lower level on most components of the test battery, but there was little evidence of a relationship between TD and syntactic psycholinguistic function. However, schizophrenic patients manifesting higher levels of TD performed at a lower level on tests sensitive to executive dysfunction and semantic impairments. CONCLUSIONS: The origins of TD seem more closely linked to deficits in executive functioning and semantic processing than to impairments in other language functions or general cognition.