Altered cortical and subcortical connectivity due to infrasound administered near the hearing threshold - Evidence from fMRI.

Markus Weichenberger,Albrecht Ihlenfeld,Bernd Ittermann,Christian Koch,Simone Kühn,Jürgen Gallinat,Caroline Garcia Forlim,Robert Kühler,Johannes Hensel,Martin Bauer,Xi-Nian Zuo

doi:10.1371/journal.pone.0174420

Abstract

In the present study, the brain’s response towards near- and supra-threshold infrasound (IS) stimulation (sound frequency < 20 Hz) was investigated under resting-state fMRI conditions. The study involved two consecutive sessions. In the first session, 14 healthy participants underwent a hearing threshold—as well as a categorical loudness scaling measurement in which the individual loudness perception for IS was assessed across different sound pressure levels (SPL). In the second session, these participants underwent three resting-state acquisitions, one without auditory stimulation (no-tone), one with a monaurally presented 12-Hz IS tone (near-threshold) and one with a similar tone above the individual hearing threshold corresponding to a ‘medium loud’ hearing sensation (supra-threshold). Data analysis mainly focused on local connectivity measures by means of regional homogeneity (ReHo), but also involved independent component analysis (ICA) to investigate inter-regional connectivity. ReHo analysis revealed significantly higher local connectivity in right superior temporal gyrus (STG) adjacent to primary auditory cortex, in anterior cingulate cortex (ACC) and, when allowing smaller cluster sizes, also in the right amygdala (rAmyg) during the near-threshold, compared to both the supra-threshold and the no-tone condition. Additional independent component analysis (ICA) revealed large-scale changes of functional connectivity, reflected in a stronger activation of the right amygdala (rAmyg) in the opposite contrast (no-tone > near-threshold) as well as the right superior frontal gyrus (rSFG) during the near-threshold condition. In summary, this study is the first to demonstrate that infrasound near the hearing threshold may induce changes of neural activity across several brain regions, some of which are known to be involved in auditory processing, while others are regarded as keyplayers in emotional and autonomic control. These findings thus allow us to speculate on how continuous exposure to (sub-)liminal IS could exert a pathogenic influence on the organism, yet further (especially longitudinal) studies are required in order to substantialize these findings.

Highlights

The question, whether infrasound (IS; sound in the very low-frequency range– 1 Hz < frequency < 20 Hz) can pose a threat to physical and mental well-being remains a much debated topic
When computing a whole-brain analysis comparing regional homogeneity (ReHo) as derived from resting-state acquisitions for different stimulation conditions, we found significantly higher local connectivity in right superior temporal gyrus (30, -15, -6) adjacent to primary auditory cortex during the near-threshold compared to the no-tone condition
In order to explore the ReHo pattern across all three conditions, we extracted betavalues from the respective clusters observed in the whole-brain contrasts

Summary

Introduction

The question, whether infrasound (IS; sound in the very low-frequency range– 1 Hz < frequency < 20 Hz) can pose a threat to physical and mental well-being remains a much debated topic. It has been shown repeatedly that IS can be perceived by humans, if administered at very high sound pressure levels (SPLs) [10,11,12,13,14,15,16,17]). Two fMRI studies revealed that exposure to a monaurally presented 12-Hz IS tone with SPLs of > 110 dB led to bilateral activation of the superior temporal gyrus (STG), which suggests that the physiological mechanisms underlying IS perception may share similarities with those involved in ‘normal hearing’, even at the stage of high-level cortical processing [18,19]

Results

Discussion

Conclusion