Keeping the inner voice inside the head, a pilot fMRI study

Introduction The inner voice is experienced during thinking in words (inner speech) and silent reading and evokes brain activity that is highly similar to that associated with external voices. Yet while the inner voice is experienced in internal space (inside the head), external voices (one's own and those of others) are experienced in external space. In this paper, we investigate the neural basis of this differential spatial localization. Methods We used fMRI to examine the difference in brain activity between reading silently and reading aloud. As the task involved reading aloud, data were first denoised by removing independent components related to head movement. They were subsequently processed using finite impulse response basis function to address the variations of the hemodynamic response. Final analyses were carried out using permutation-based statistics, which is appropriate for small samples. These analyses produce spatiotemporal maps of brain activity. Results Reading silently relative to reading aloud was associated with activity of the where auditory pathway (Inferior parietal lobule and middle temporal gyrus), and delayed activity of the primary auditory cortex. Conclusions These pilot data suggest that internal space localization of the inner voice depends on the same neural resources as that for external space localization of external voices-the where auditory pathway. We discuss the implications of these findings on the possible mechanisms of abnormal experiences of the inner voice as is the case in verbal hallucinations.

Automated summary

This study used fMRI to investigate the differences in brain activity between reading silently and reading aloud. The results indicated that reading silently compared to reading aloud was associated with activity in the auditory pathway and delayed activity in the primary auditory cortex.