Evaluation of missing fundamental phenomenon in the human auditory cortex.
OBJECTIVE
Harmonic complex tones consisting of four or more continuous harmonics of a certain stem frequency are perceived as the pitch of the fundamental frequency tone, it is referred to as the missing fundamental phenomenon (MFP). It is considered that the MFP is produced in the central auditory system, not in the periphery. However, it remains unclear where and how complex sounds is integrated. Using 306ch magnetoencephalography (MEG), we investigated when and where the MFP was integrated in the auditory cortex.


METHODS
We examined six subjects who were selected by MEG in 12 healthy right-handed adult volunteers with normal auditory sensation. Ears were randomly stimulated with five different complex tones consist of fundamental frequency tone and harmonic complex tones. The location and direction of equivalent current dipoles (ECD) were evaluated at P50 and N100 in the right temporal lobe by MEG. Dispersion of the source of ECD was respectively evaluated on their brain MRI.


RESULTS
Stimulation of ears with harmonic complex tones and the stem frequency tone revealed the localization of P50 and N100 ECD in the transverse temporal gyrus and their peripheral superior temporal gyrus. Although the sources of P50 ECD for harmonic complex tones and the fundamental tone were varied around the transverse temporal gyrus and superior temporal gyrus, the sources of N100 ECD were almost identical at the transverse temporal gyrus, demonstrating the MFP. This phenomenon were similarly observed, even when dichotic listening were stimulated.


CONCLUSIONS
These findings suggest that the MFP occurs in the transverse temporal gyrus and the superior temporal gyrus, which are the primary auditory cortex, between P50 and N100.
Matsuwaki
Yoshinori
Y
Department of Otorhinolaryngology, Tokyo Dental College Ichikawa General Hospital, 5-11-13 Sugano, Ichikawa-shi, Chiba 272-0824, Japan.
Nakajima
Tsuneya
T
Ookushi
Tetsushi
T
Iimura
Jirou
J
Kunou
Kiyoshi
K
Nakagawa
Masafumi
M
Shintani
Masuro
M
Moriyama
Hiroshi
H
Ishikawa
Tatsuya
T
D000161:Acoustic Stimulation / Q000379:methods; D001303:Auditory Cortex / Q000033:anatomy & histology* / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography / Q000379:methods; D013702:Temporal Lobe / Q000033:anatomy & histology / Q000502:physiology