Subjective loudness and reality of auditory verbal hallucinations and activation of the inner speech processing network

Abstract

Background: One of the most influential cognitive models of auditory verbal hallucinations (AVH) suggests that a failure to adequately monitor the production of one's own inner speech leads to verbal thought being misidentified as an alien voice. However, it is unclear whether this theory can explain the phenomenological complexity of AVH. We aimed to assess whether subjective perceptual and experiential characteristics may be linked to neural activation in the inner speech processing network.

Methods: Twenty-two patients with schizophrenia and AVH underwent a 3-T functional magnetic resonance imaging scan, while performing a metrical stress evaluation task, which has been shown to activate both inner speech production and perception regions. Regions of interest (ROIs) comprising the putative inner speech network were defined using the Anatomical Automatic Labeling system. Correlations were calculated between scores on the "loudness" and "reality" subscales of the Auditory Hallucination Rating Scale (AHRS) and activation in these ROIs. Second, the AHRS subscales, and general AVH severity, indexed by the Positive and Negative Syndrome Scale, were correlated with a language lateralization index.

Results: Louder AVH were associated with reduced task-related activity in bilateral angular gyrus, anterior cingulate gyrus, left inferior frontal gyrus, left insula, and left temporal cortex. This could potentially be due to a competition for shared neural resources. Reality on the other hand was found to be associated with reduced language lateralization.

Conclusion: Strong activation of the inner speech processing network may contribute to the subjective loudness of AVH. However, a relatively increased contribution from right hemisphere language areas may be responsible for the more complex experiential characteristics, such as the nonself source or how real AVH are.

Fig. 1.

Shows the Pattern of Activation Derived during the Phonological Task Condition of the Metrical Stress Evaluation Task, at the Group Level (n = 22). Group results are displayed for illustrative purposes, as for the ROI analysis, individual subject images were analyzed at the first level to produce estimates for the contrast of interest (P < .001, uncorrected). The phonology condition was contrasted with the resting baseline, rather than the active semantic control condition, in order to maximize the potential to identify linguistic activity in the predefined language-related ROI’s. Estimates of the signal change for the contrast of interest were then extracted using the MarsBaR toolbox for SPM.

Fig. 2.

Shows the Scatterplot of the Negative Correlation between the Language Lateralization Index and Scale “Reality of AVH,” Which Indexes the Global Experiential Sense of How Real the Hallucinated Voices Appear to the Subject, as Indicated on a Scale from 0 (Not Real at All) to 5 (Very Real).