Auditory verbal hallucinations and the interhemispheric auditory pathway in chronic schizophrenia

Abstract

Objectives: The interhemispheric auditory pathway has been shown to play a crucial role in the processing of acoustic stimuli, and alterations of structural and functional connectivity between bilateral auditory areas are likely relevant to the pathogenesis of auditory verbal hallucinations (AVHs). The aim of this study was to examine this pathway in patients with chronic schizophrenia regarding their lifetime history of AVHs.

Methods: DTI scans were acquired from 33 healthy controls (HC), 24 schizophrenia patients with a history of AVHs (LT-AVH) and nine schizophrenia patients without any lifetime hallucinations (N-LT-AVH). The interhemispheric auditory fibre bundles were extracted using streamline tractography. Subsequently, diffusivity indices, namely Fractional Anisotropy (FA), Trace, Mode, Axial and Radial diffusivity, were calculated.

Results: FA was decreased over the entire pathway in LT-AVH compared with N-LT-AVH. Moreover, LT-AVH displayed decreased FA and Mode as well as increased radial diffusivity in the midsagittal section of the fibre tract.

Conclusions: These findings indicate complex microstructural changes in the interhemispheric auditory pathway of schizophrenia patients with a history of AVHs. Alterations appear to be absent in patients who have never hallucinated.

Keywords: MRI; auditory verbal hallucinations; brain imaging; diffusion tensor imaging; schizophrenia.

Figure 1. The interhemispheric auditory pathway

The orange fibres illustrate the interhemispheric auditory pathway while the blue fibres result from tractography of the entire CC. The midsagittal ROI (in blue) and coronal ROIs (in green) are depicted within the orange box.

Figure 2. FA (midsagittal)

Scatterplot illustrating the variations in FA between groups for the midsagittal slice of the interhemispheric auditory pathway. Significant difference between all groups (ANOVA; p = .019) and significantly diminished FA values in (LT)AVH compared to N(LT)AVH (t-test; p = .029) and to HC (t-test; p = .027). HC: healthy control subjects; N(LT)AVH: schizophrenic patients without lifetime-hallucinations; (LT)AVH: schizophrenic patients with lifetime-hallucinations; FA: fractional anisotropy. The black bars represent FA means and the asterisks represent significant between-group differences.

Figure 3. Mode (midsagittal)

Scatterplot illustrating the variations in Mode between groups for the midsagittal slice of the interhemispheric auditory pathway. Significantly diminished Mode values in (LT)AVH compared to N(LT)AVH (t-test; p = .029) and to HC (t-test; p = .001). HC: healthy control subjects; N(LT)AVH: schizophrenic patients without lifetime-hallucinations; (LT)AVH: schizophrenic patients with lifetime-hallucinations. The black bars represent Mode means and the asterisk represents the significant between-group difference.

Figure 4. Radial Diffusivity (midsagittal)

Scatterplot illustrating the variations in Radial Diffusivity between groups for the midsagittal slice of the interhemispheric auditory pathway. Significantly increased Radial Diffusivity values in (LT)AVH compared to HC (t-test; p = .021) and marginally increased values in (LT)AVH compared to N(LT)AVH (t-test; p = .089). HC: healthy control subjects; N(LT)AVH: schizophrenic patients without lifetime-hallucinations; (LT)AVH: schizophrenic patients with lifetime-hallucinations. The black bars represent Radial means and the asterisk represents the significant between-group difference.