Abstract
Airborne infrasound (IS; emitted by e.g., large machinery, wind farms) is ubiquitous in technologized environments. Health hazards are controversially discussed at present. This study investigated long-term effects of IS on brain (regional grey matter volume; rGMV) and behavior in humans. Specifically engineered infrasonic (6 Hz, 80–90 dB) vs. sham devices were installed in participants’ (N = 38) bedrooms and active for 28 nights. Somatic and psychiatric symptoms, sound-sensitivity, sleep quality, cognitive performance, and structural MRI were assessed pre-post. Null findings emerged for all behavioral variables. Exploratory analyses revealed a trend (p = .083) with individuals exposed to IS reporting more physical weakness at post-test (d = 0.38). Voxel-based morphometry (VBM) revealed no rGMV increases, but there were decreases within clusters in the cerebellum VIIIa (bilateral) and left angular gyrus (BA39) in verum. In conclusion, IS does not affect healthy individuals on a global scale. However, future trials should consider more fine-grained specific effects, combining self-report with physiological assessments, particularly directed at bodily sensations and perception. As no brain-behavior-links could be established, the identified grey matter decline cannot be interpreted in terms of potential harmfulness vs. improvement through IS-exposure. Parameters that may best reflect brain changes as established in the present study include motor function, sensory processing/ bodily- and motor-perceptions, working memory, and higher auditory processing (i.e., language-related tasks), which are hence potential target variables for further research.
Highlights
Airborne infrasound (IS; emitted by e.g., large machinery, wind farms) is ubiquitous in technologized environments
It shall be noted that the hearing threshold, provided high sound pressure levels (SPLs), is variable, and a hearing sensation can be provoked at infrasonic frequencies
38 participants fully took part in the study, 38 pre-post datasets were available for analysis
Summary
Airborne infrasound (IS; emitted by e.g., large machinery, wind farms) is ubiquitous in technologized environments. Annoyance is reported by about 10% of individuals living in proximity to relevant infrasonic or low-frequency sources[6] Both reviews correspond in their call for methodologically well-designed long-term studies, which are lacking at present. The signal was evident at SPLs between 90 and 110 dB for audible infrasonic and low frequencies between 12 and 500 Hz7 Another pilot study conducted by our research group found that IS generates brain activities within the auditory cortex down to a frequency of 8 Hz8, if IS is presented at SPLs above the hearing threshold. A further study investigated restingstate brain activity and found it to be significantly altered by near-threshold ( inaudible) IS at a frequency of 12 Hz. Higher local connectivity in the right superior temporal gyrus (primary auditory cortex), the anterior cingulate cortex, and the right amygdala, was identified. While IS does not alter hearing thresholds at audible frequencies, vice versa audible noise increased the thresholds of IS tending to reduce the load of IS on humans in an exposure s ituation[11]
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