Auditory cortex stimulation by low-frequency tones-an fMRI study.
OBJECTIVE
Low-frequency tones (LFT) and infrasound (IS) are looked upon as potentially hazardous to human health. We aimed at assessing LFT/IS-induced activation of the auditory cortex by using fMRI.


METHODS
fMRI was used to investigate LFT/IS perception in 17 healthy volunteers. Short tone bursts of 12, 36, 48 and 500 Hz were delivered directly into the right external ear canal through a 12-m long silicone tube and an ear plug. Sound pressure levels (SPL) and spectral analysis of the stimuli and scanner noise were measured in situ by using a metal-free optical microphone and a fiber-optic cable.


RESULTS
SPL-dependent activation of the superior temporal gyrus, i.e. Brodmann areas (BA) 41 and 42 as well as BA 22, was delineated subsequent to acoustic stimulation with 12-, 48- and 500-Hz stimuli. Thresholds for LFT/IS-induced brain activation were between 110 and 90 dB SPL in normal hearing subjects. Spectral analysis revealed the occurrence of harmonics together with LFT, of which 36-Hz harmonics interfered with IS exposure at 12 Hz as well as scanner noise.


CONCLUSIONS
Our results provide evidence that auditory cortex activation may be induced by LFT/IS exposure, depending on sound pressure levels applied. Clinical implications of our findings will have to be addressed by subsequent studies involving patients presumptively suffering from LFT-dependent disorders.
Dommes
E
E
Department of Neuroradiology, Charité-Universitary Medicine Berlin, Charitéplatz 1, 10117 Berlin, Germany. Esther.dommes@charite.de
Bauknecht
H C
HC
Scholz
G
G
Rothemund
Y
Y
Hensel
J
J
Klingebiel
R
R
D000161:Acoustic Stimulation; D000162:Acoustics; D000328:Adult; D001303:Auditory Cortex / Q000502:physiology*; D001307:Auditory Perception / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D011312:Pressure; D013018:Sound Spectrography