Right hemisphere language functions and schizophrenia: the forgotten hemisphere?

Area of Science:

• Neuroscience
• Psycholinguistics
• Cognitive Psychology

Background:

• Right hemisphere (RH) plays a critical role in higher-order language functions essential for social communication.
• These RH-mediated functions include understanding humor, sarcasm, metaphors, indirect requests, and emotional prosody.
• Impaired segregation of RH and left hemisphere (LH) language functions is hypothesized as a core deficit in psychosis.

Purpose of the Study:

• To review the importance of RH language functions in social communication.
• To propose a hypothesis linking psychosis to a failure in hemispheric language segregation.
• To outline a bi-hemispheric theory of language and its relation to schizophrenia.

Main Methods:

• Review of lesion studies in stroke patients.
• Analysis of dichotic listening and functional imaging studies in healthy individuals.
• Examination of behavioral evidence from patients with schizophrenia and affective psychoses.

Main Results:

• RH mediates key language functions like discourse planning, humor comprehension, and emotional prosody.
• Patients with schizophrenia exhibit poor performance on tests of these RH-mediated language functions.
• These deficits likely contribute significantly to social interaction difficulties in schizophrenia.

Conclusions:

• A failure in the segregation of RH and LH language functions may underlie psychosis.
• RH language deficits contribute to social communication impairments in schizophrenia.
• Future research should consider the consequences of failed lateralization in both hemispheres for language functions.