Objective The brain bases of musical hallucinations (MH) is not understood. A major problem in this effort is the lack of a suitable method to experimentally manipulate MH during the course of experiment. In this work we present a method to systematically manipulate MH using an external masker stimulus. Furthermore, we make use of the manipulation of MH to compare brain activity as a function of intensity of hallucination. We then combine our results with the computational theories of brain function to propose a model of how the brain generates and maintain MH.
Method We used a residual inhibition (RI) paradigm to manipulate MH. In the RI, an external masking stimulus (music in the current work) is presented which suppresses hallucinations. The intensity of hallucinations remain low after the offset of masking stimulus before the hallucinations come back to normal level. We make use of the RI to manipulate MH while brain activity being acquired using Magnetoencephalography (MEG).
Results Our results show that (i) MH can residually suppress the MH for up to a minute (ii) Source-space analysis capable of single-subject inference defined left-lateralised power increases, associated with stronger hallucinations, in the gamma band in left anterior superior temporal gyrus, and in the beta band in motor cortex and posteromedial cortex.
Conclusion The data indicate that these areas form a crucial network in the generation of MH, and are consistent with a model in which MH are generated by persistent reciprocal communication in a predictive coding hierarchy.