Musical hallucinations

A brain basis for musical hallucinations
July 15, 2015 – 09:34 am
The Necessity of Musical

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

Keywords

  • Musical hallucinations;
  • Magnetoencephalography;
  • Auditory cortex;
  • Gamma oscillations;
  • Beta oscillations;
  • Predictive coding

1. Introduction

Hallucinations are false percepts in the waking state that are not consequences of stimuli in the external environment, and can involve any sensory modality. Musical hallucinations (MH) are a type of auditory hallucination characterized by perception of musical sounds in the absence of any external source of music. Their content is often familiar and can be instrumental, vocal or both. While hallucinations of music can occasionally result from focal brain lesions and psychiatric disorders (, and ) the most common cause is hearing loss in the absence of other pathology. 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.

Although a number of case studies involving MH have been reported in the literature (for reviews see and ), there are only a few studies that have investigated the brain bases for MH. 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 (, and ) often separated by several days, or compared brain activity across different population of subjects, with and without hallucinations ( and ). A wide range of cortical and sub-cortical areas, which are inconsistent across studies, have been implicated in MH.

Source: www.sciencedirect.com
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