A possible contributory mechanism for impaired idiom perception in schizophrenia

In this review, we focus on the ability of people with schizophrenia to correctly perceive the meaning of idioms; figurative language expressions in which intended meaning is not derived from the meaning of constituent words. We collate evidence on how idiom perception is impaired, ascertain the clinical relevance of this impairment, and consider possible psychological and neural mechanisms behind the impairment. In reviewing extant literature, we searched the PubMed database, from 1975-2014, focussing on articles that directly concerned schizophrenia and idioms, with follow up searches to explore the viability of possible underlying mechanisms. We learn that there is clear evidence of impairment, with a tendency to err towards literal interpretations unless the figurative meaning is salient, and despite contextual cues to figurative interpretations. Given the importance of idioms in everyday language, the potential impact is significant. Clinically, impaired idiom perception primarily relates to positive symptoms of schizophrenia, but also to negative symptoms. The origins of the impairment remain speculation, with impaired executive function, impaired semantic functions, and impaired context processing all proposed to explain the phenomenon. We conclude that a possible contributory mechanism at the neural level is an impaired dorsolateral prefrontal cortex system for cognitive control over semantic processing.