Background: Previous studies have reported significant correlations, indicating an emerging relationship, between severity of auditory hallucinations and reduced size of temporal lobe cortical regions implicated in language processing. The present study used high-resolution magnetic resonance imaging (MRI) scanning, along with assessment of functional lateralization via a dichotic listening task (DLT), to extend these findings.
Methods: Thirty patients with schizophrenia and a history of auditory hallucinations participated in the study. All were completely right-handed. Eleven subjects were currently hallucinating at the time of the study. Volumetric T1-weighted MRI scans were obtained and regions of interest were manually traced using the BRAINS package (Andreasen et al 1993). Whole brain, bilateral temporal lobe, and anterior superior temporal gyrus volumes were calculated. Subjects completed a binaural consonant-vowel DLT.
Results: Increased severity of hallucinatory experience was significantly associated with smaller left anterior superior temporal gyrus volumes. Current hallucinators demonstrated a reduction in right ear advantage on the DLT.
Conclusions: The results suggest that auditory hallucinations are subserved by a trait-like dysfunction in language-related neural networks, of which the superior temporal cortex forms one component. The findings are also consistent with theories proposing abnormal lateralization in the etiology of auditory hallucinations.