The Journal of Neurophysiology Vol. 83 No. 6 June 2000, pp. 3548-3558
Copyright ©2000 by the American Physiological Society
Inaudible High-Frequency Sounds Affect Brain
Activity: Hypersonic Effect
Tsutomu
Oohashi,1,2
Emi
Nishina,3
Manabu
Honda,4,5
Yoshiharu
Yonekura,4,6
Yoshitaka
Fuwamoto,7
Norie
Kawai,8,9
Tadao
Maekawa,10
Satoshi
Nakamura,6
Hidenao
Fukuyama,4 and
Hiroshi
Shibasaki4
1Department of KANSEI Brain Science,
ATR Human Information Processing Research Laboratories, Kyoto
619-0288; 2Department of Network Science, Chiba
Institute of Technology, Narashino 275-0016;
3Human Interface Research and Development
Section, National Institute of Multimedia Education, Chiba 261-0014;
4Department of Brain Pathophysiology, Kyoto
University School of Medicine, Kyoto 606-8507;
5Laboratory of Cerebral Integration, National
Institute for Physiological Sciences, Okazaki 444-8585;
6Biomedical Imaging Research Center, Fukui
Medical University, Fukui 910-1193; 7Department
of Environmental and Information Sciences, Yokkaichi University,
Yokkaichi 512-8512; 8Institute of Community
Medicine, University of Tsukuba, Tsukuba 305-8577;
9Foundation for Advancement of International
Science, Tsukuba 305-0005; and 10Art and
Technology Project, ATR Media Integration & Communications Research
Laboratories, Kyoto 619-0288, Japan
Oohashi, Tsutomu,
Emi Nishina,
Manabu Honda,
Yoshiharu Yonekura,
Yoshitaka Fuwamoto,
Norie Kawai,
Tadao Maekawa,
Satoshi Nakamura,
Hidenao Fukuyama, and
Hiroshi Shibasaki.
Inaudible High-Frequency Sounds Affect Brain
Activity: Hypersonic Effect. J. Neurophysiol. 83: 3548-3558, 2000. Although it is generally accepted
that humans cannot perceive sounds in the frequency range above 20 kHz,
the question of whether the existence of such "inaudible"
high-frequency components may affect the acoustic perception of audible
sounds remains unanswered. In this study, we used noninvasive
physiological measurements of brain responses to provide evidence that
sounds containing high-frequency components (HFCs) above the audible
range significantly affect the brain activity of listeners. We used the
gamelan music of Bali, which is extremely rich in HFCs with a
nonstationary structure, as a natural sound source, dividing it into
two components: an audible low-frequency component (LFC) below 22 kHz
and an HFC above 22 kHz. Brain electrical activity and regional
cerebral blood flow (rCBF) were measured as markers of neuronal
activity while subjects were exposed to sounds with various
combinations of LFCs and HFCs. None of the subjects recognized the HFC
as sound when it was presented alone. Nevertheless, the power spectra
of the alpha frequency range of the spontaneous electroencephalogram (alpha-EEG) recorded from the occipital region increased with statistical significance when the subjects were exposed to sound containing both an HFC and an LFC, compared with an otherwise identical
sound from which the HFC was removed (i.e., LFC alone). In contrast,
compared with the baseline, no enhancement of alpha-EEG was evident
when either an HFC or an LFC was presented separately. Positron
emission tomography measurements revealed that, when an HFC and an LFC
were presented together, the rCBF in the brain stem and the left
thalamus increased significantly compared with a sound lacking the HFC
above 22 kHz but that was otherwise identical. Simultaneous EEG
measurements showed that the power of occipital alpha-EEGs correlated
significantly with the rCBF in the left thalamus. Psychological
evaluation indicated that the subjects felt the sound containing an HFC
to be more pleasant than the same sound lacking an HFC. These results
suggest the existence of a previously unrecognized response to complex
sound containing particular types of high frequencies above the audible
range. We term this phenomenon the "hypersonic effect."
