Superior temporal gyral volumes and laterality correlates of auditory hallucinations in schizophrenia

Background: Previous studies have reported significant correlations, indica ting an emerging relationship, between severity of auditory hallucinations and reduced size of temporal lobe cortical regions implicated in language p rocessing. The present study used high-resolution magnetic resonance imagin g (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 hallu cinations participated in the study. All were completely right-handed. Elev en subjects were currently hallucinating at the time of the study. Volumetr ic T1-weighted MRI scans were obtained and regions of interest were manuall y traced using the BRAINS package (Andreasen et al 1993). Whole brain, bila teral temporal lobe, and anterior superior temporal gyrus volumes were calc ulated. Subjects completed a binaural consonant-vowel DLT. Results: Increased severity of hallucinatory experience was significantly a ssociated with smaller left anterior superior temporal gyrus volumes. Curre nt 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 con sistent with theories proposing abnormal lateralization in the etiology of auditory hallucinations. Biol Psychiatry 1999;46:955-962 (C) 1999 Society o f Biological Psychiatry.