We used whole-head magnetoencephalography (MEG) to contrast oscillatory brain activity during periods of high and low hallucinations. The present study focuses on a subject, who is at present unique in the literature, whose MH could be residually inhibited using short periods of music as a masker stimulus. While the utility of RI in tinnitus is well-established, the same phenomenon has not been reported in MH. Contrasting this period of suppressed tinnitus with a nearby period of unsuppressed tinnitus allows measurement of brain correlates of tinnitus in the absence of any external sound stimulation ( Kahlbrock & Weisz, 2008 Osaki etВ al., 2005 Sedley, Teki, Kumar, Barnes, etВ al., 2012). RI involves presenting an auditory вЂmaskerвЂ™ stimulus for a period of time, and after this stimulus ends, there is a period of time in which the phantom percept remains reduced in intensity. We assessed here whether residual inhibition (RI), which has been successfully used in tinnitus research ( Feldmann, 1981 Roberts, 2007 Sedley, Teki, Kumar, Barnes, etВ al., 2012), might also be applied to MH. Measuring the brain activity that changes with MH in the same subject in the same session, requires a paradigm in which the MH can be altered at defined times during the course of the experiment. We consider here whether a common physiological mechanism might exist that could have different anatomical instantiations to explain the variety of phenomenology and substrates previously reported. Given the variation in phenomenology in MH, and in subject factors such as musical expertise, the possibility of such inter-individual variation in neuro-anatomical substrate must be seriously considered. Comparing across sessions may highlight changes in neural activity associated with factors other than hallucination intensity, and comparing across subjects might fail to detect parts of the neural substrate that show inter-individual variation or erroneously imply that certain areas are involved in all subjects. A wide range of cortical and sub-cortical areas, which are inconsistent across studies, have been implicated in MH.ДЄ possible contribution to the lack of converging results amongst previous studies is the absence of a paradigm to measure brain activity associated with MH in individual subjects within a single session. In order to determine how the states of a hallucinating brain differ from that of a normal brain, these studies have either compared brain activities in the same subject but in two different sessions ( Griffiths, 2000 Kasai, Asada, Yumoto, Takeya, & Matsuda, 1999 Shoyama etВ al., 2010) often separated by several days, or compared brain activity across different population of subjects, with and without hallucinations ( Shinosaki etВ al., 2003 Vanneste, Song, & De Ridder, 2013). This latter group raises the question of how hearing loss alone can lead to the development of complex MH, which is the focus of this study.ДЄlthough a number of case studies involving MH have been reported in the literature (for reviews see Evers, 2006 Evers & Ellger, 2004), there are only a few studies that have investigated the brain bases for MH. While hallucinations of music can occasionally result from focal brain lesions and psychiatric disorders ( Keshavan, David, Steingard, & Lishman, 1992 Warren & Schott, 2006 Saba & Keshavan, 1997) the most common cause is hearing loss in the absence of other pathology ( Berrios, 1990). Their content is often familiar and can be instrumental, vocal or both. Musical hallucinations (MH) are a type of auditory hallucination characterized by perception of musical sounds in the absence of any external source of music. Hallucinations are false percepts in the waking state that are not consequences of stimuli in the external environment, and can involve any sensory modality. 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.

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. Magnetoencephalography (MEG) allowed us to examine variation in the underlying oscillatory brain activity in different states. We report here a human subject whose MH were residually inhibited by short periods of music. Residual inhibition, transient suppression of a phantom percept after the offset of a masking stimulus, has been used in the study of tinnitus. One obstacle to understanding has been the lack of a method to manipulate the intensity of hallucination during the course of experiment. The physiological basis for musical hallucinations (MH) is not understood.

Hallucination experiment