Conference_programme: 5: Audiology

Lecture: Auditory functional MRI activation maps in response to low-frequency and infrasound stimulation

Author(s): Uppenkamp Stefan, Netter Kirsten, Behler Oliver

Summary:
Infrasound in the human environment may be generated by large industrial plants or wind farms, and there is an increasing concern about possible negative effects on well-being and health. However, the perceptual mechanisms for infrasound stimuli in the human auditory system are not completely understood yet. In this study, detection thresholds for sinusoids in the frequency range from 256 Hz down to 8 Hz were determined for a group of 20 normal hearing listeners, using monaural stimulation via a loudspeaker sound source coupled to the ear canal by a long silicone rubber tube. The absolute thresholds collected in our study are largely in line with previous results, both for monaural stimulation as well as for free field conditions with stimulation of both ears. Following the threshold measurements, categorical loudness scaling was performed, to determine loudness growth with level as well as the individual uncomfortable levels. \nBased on the results from the loudness scaling procedure, the stimulus level for a successive functional MRI activation study was chosen individually to lie between the individual detection threshold and the uncomfortable level. Using the same sound source as before, that is, monaural stimulation via flexible tube coupled to the ear canal, a subgroup of the participants listened to tonal stimuli at the frequencies 128 Hz (well within the classical audible range), 32 Hz (at the lower limit of melodic pitch for tonal stimulation), as well as 8 Hz (infrasound range), and a condition with no stimulation as baseline, while fMRI scanning was performed using an echo-planar imaging sequence on a 3-Tesla MRI scanner.\nWhilst the 128-Hz-stimuli evoke a slightly lateralized activation pattern, largely restricted to primary auditory cortex as expected, the results for infrasound stimulation are much less distinct, but rather distributed across various cortical regions, including auditory areas, but not restricted to primary auditory cortex.\n

Corresponding author

Name: Dr Stefan Uppenkamp

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Country: Germany