Language-related gamma EEG frontal reduction is associated with positive symptoms in schizophrenia patients

Abstract

Objectives: Frontal hypoactivation has been consistently found in schizophrenia. We hypothesized that patients' deficit is asymmetrical, i.e., centred over the left frontal locations, associated with loss of language-related asymmetry, and correlated with positive symptoms.

Method: The amplitude of EEG gamma band (36-48Hz) was measured during the processing of three linguistic (Phonological vs. Semantic vs. Visuo-perceptual) tasks and used as index of activation/connectivity in 18 schizophrenia patients and 18 healthy participants.

Results: Healthy controls showed higher gamma in frontal sites, revealing a significantly greater left vs. right asymmetry in all linguistic tasks, whereas patients exhibited decreased and bilateral gamma amplitude (i.e., reduced activation/connectivity) in frontal regions. The patients' left hypofrontality during phonological processing was positively correlated with higher levels of Delusions (P1) and Hallucination (P3) PANSS subscales. A significantly greater left posterior gamma amplitude was found in patients compared with controls.

Conclusion: Results suggest, in schizophrenia patients, a functional deficit of left frontal regions including Broca's area, a key site playing a fundamental hierarchical role between and within hemispheres which integrates many basic processes in linguistic and conceptual organization. The significant correlation between lack of the left anterior asymmetry and increased positive symptoms is in line with Crow's hypothesis postulating the aetiological role of disrupted linguistic frontal asymmetry on the onset of the key symptoms of schizophrenia.

Keywords: Delusions; Gamma EEG rhythm; Hallucination; Lateralization; Psychosis.