The neural correlates of subjectively perceived and passively matched loudness perception in auditory phantom perception.

Dirk De Ridder,Sven Vanneste,Marco Congedo

doi:10.1002/brb3.331

Abstract

IntroductionA fundamental question in phantom perception is determining whether the brain creates a network that represents the sound intensity of the auditory phantom as measured by tinnitus matching (in dB), or whether the phantom perception is actually only a representation of the subjectively perceived loudness.MethodsIn tinnitus patients, tinnitus loudness was tested in two ways, by a numeric rating scale for subjectively perceived loudness and a more objective tinnitus-matching test, albeit it is still a subjective measure.ResultsPassively matched tinnitus does not correlate with subjective numeric rating scale, and has no electrophysiological correlates. Subjective loudness, in a whole-brain analysis, is correlated with activity in the left anterior insula (alpha), the rostral/dorsal anterior cingulate cortex (beta), and the left parahippocampus (gamma). A ROI analysis finds correlations with the auditory cortex (high beta and gamma) as well. The theta band links gamma band activity in the auditory cortex and parahippocampus via theta–gamma nesting.ConclusionsApparently the brain generates a network that represents subjectively perceived tinnitus loudness only, which is context dependent. The subjective loudness network consists of the anterior cingulate/insula, the parahippocampus, and the auditory cortex. The gamma band activity in the parahippocampus and the auditory cortex is functionally linked via theta–gamma nested lagged phase synchronization.

Highlights

A fundamental question in phantom perception is determining whether the brain creates a network that represents the sound intensity of the auditory phantom as measured by tinnitus matching, or whether the phantom perception is only a representation of the subjectively perceived loudness
Tinnitus loudness was tested in two ways: a numeric rating scale between 0 and 10 was used to evaluate the subjectively perceived tinnitus loudness based on the question: ‘How loud is your tinnitus?’ (0 = no tinnitus and 10 = as loud as imaginable’)
This is in line with what has recently been proposed to be a major function for the parahippocampus, namely, contextually influencing perception (Aminoff et al 2013). This functional connectivity between the left parahippocampal area and auditory cortex has already been shown, using resting state functional magnetic resonance imaging (fMRI), to be an essential neurophysiological feature of tinnitus (Maudoux et al 2012). We propose that this functional connectivity is clinically linked to the subjectively perceived loudness, and explain the underlying mechanism involved: theta–gamma nesting

Summary

Introduction

A fundamental question in phantom perception is determining whether the brain creates a network that represents the sound intensity of the auditory phantom as measured by tinnitus matching (in dB), or whether the phantom perception is only a representation of the subjectively perceived loudness. Brain mechanisms have evolved to fill in the missing information and tinnitus might represent a filling in missing mechanism (De Ridder et al 2014a), as most patients perceive the tinnitus in the deafferented frequencies (Norena et al 2002), and initially attribute it as coming from the environment. This could suggest that principles of normal sensory perception might apply to auditory phantom perception

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Discussion

Conclusion