Fiber tracts altered in auditory hallucinations
July 19, 2004

Auditory hallucinations in people with schizophrenia are associated with activation of brain regions involved in processing external stimuli, new research shows.

The finding may explain why patients are unable to distinguish self-generated thoughts from external voices, claim the study's authors in the Archives of General Psychiatry.

Daniela Hubl (University Hospital of Clinical Psychiatry, Bern, Switzerland) and team used magnetic resonance diffusion tensor imaging to investigate the connections between frontal and pariotemporal speech-related areas of the brain in vivo.

Fractional anisotropy was assessed in 13 patients prone to auditory hallucinations, 13 patients with schizophrenia but no hallucinations, and 13 healthy controls. Structural MRI was conducted in the same session.

Patients with hallucinations had significantly higher white matter directionality in the lateral parts of the temporoparietal section of the arcuate fasciculus and in parts of the anterior corpus callosum compared with control subjects and patients without hallucinations, Hubl's team reports.

Furthermore, there were significant differences in the brains of patients with and without hallucinations; these were most pronounced in the left hemispheric fiber tracts, including the cingulate bundle.

In their discussion, the authors comment that auditory hallucinations and inner speech are often closely related with respect to content - indeed, such hallucinations are sometimes reported as "thoughts becoming loud".

They conclude that, during inner speech, alterations in white matter fiber tracts lead to abnormal coactivation in regions related to the acoustical processing of external stimuli.

"These alterations may have a developmental origin and may contribute to an understanding of how internally generated language is perceived to be generated externally," they add.

Arch Gen Psychiatry 2004; 61: 658-668