80Hz変調周波数追随反応に対するネコ蝸牛神経核の関与 Contribution of Cochlear Nucleus to 80Hz Amplitude-Modulation Following Response




    • 鈴木 豊 SUZUKI Yutaka
    • 山形大学医学部耳鼻咽喉科学教室 Department of Otorhinolaryngology, Yamagata University School of Medicine


(背景)周波数特異性の高正弦波的振幅変調音(SAM音)を刺激音として得られる聴性定常反応は変調周波数追随反応(AMFR)と呼ばれている.聴性定常反応の刺激頻度としては40Hzを用いた報告がほとんどあり,40HzAMFRは睡眠時に検査を行う乳幼児への他覚的聴力検査としての臨床応用は困難とされてきた.一方睡眠時の被験者を対象とした場合,変調周波数を80から100Hzにすると聴力レベル付近まで反応の検出が可能である.AMFRの起源は確定されていないが40HzAMFRは覚醒時,80HzAMFRは睡眠時に良好な反応が得られることから,変調周波数の違いや意識レベルはり起源が異なる可能性がある.蝸牛神経核および下丘中心核には振幅変調音に同期発火する細胞が多数分布しており,こ<br>れらとAMFRとの関連について言されているが,本研究の目的は80HzAM-FRの形成に蝸牛神経核が関与しているかどうかを検討することにある.(方法)麻酔時のネコを用いクリック短音及びSAMに対する反応の蝸牛神経核内とその周辺における電位分布を検討した.次いで蝸牛神経核内の反応がfar fieldpotentialとして記録可能かを確認する目的で,蝸牛神経核を含む脳断面とで一定間隔の位置で変調周波数80HzのSAM音に対する反応波形を記録し,脳内においてnear field potentialからfar field potentialに移行していく過程における記録波形の位相の変化を検討した.(結果)蝸牛神経核内で,発生源の異なると推定される2つの電位,すなわち変調波様の波形と刺激音様の波形の重畳した波形が記録され,前者はAMFRとの関係が示唆された.この変調波様反応波形は蝸牛神経核周囲では急激な位相の変動を示したが,小脳表面に近づくにつれて安定した固定電位を形成していた.(結論)以上より蝸牛神経核は変調周波数追髄反応の起源の1つであることが示された.

The steady-state response (SSR) evoked by a sinusoidally amplitude-modulated (SAM) tone is known as an amplitude-modulation following response (AMFR). The amplitude of the SSR which is elicited using clicks or tone bursts at a stimulus rate of 40Hz, decreases during sleep. The same trend is also observed for AMFR at a modulation rate of 40Hz. Thus it was difficult to analyzing SSR and AMFR is therefore difficult in young children, since objective audiometry just be performed while the child is asleep. Recent reports, however, have announced that the AMFR can be clearly detected at higher MFs (modulation frequencies), especially at frequencies between 80 and 100Hz. This finding has proven useful in objective audiometry for young children, Recent reports have also suggested that AMFRs arise from multiple sources, including the auditory cortex and auditory nuclei in the brainstem. However, the exact sources of ANIFRs have not been clarified. The purpose of this study is to clarify the contribution of the cochlear nucleus in evoking ANIFRs at a modulation frequency of 80Hz.<br>The near-field potentials elicited with a SAM tone were recorded from the ipsilateral cochlear nucleus and its vicinity in cats. The near-field potential recorded by bipolar electrodes consisted of two different components: a low frequency component similar to the stimulus envelope (modulation), and a high frequency component similar to the actual stimulus tone. A sequence of field potentials was recorded using monopolar electrodes located at different sites within the cochlear nucleus and in its vicinity and on the surface of the cerebellum to confirm that near-field potentials elicited by SAM tones at a MF of 80Hz in the cochlear nucleus can be recorded at the surface of the cerebellum or at other brain sites. The phase of the 80Hz frequency component of the potentials elicited by a SAM tone at a MF of 80Hz was then analyzed using a fast Fourier transformation. A contour map was produced using the means of the Fourier component phases corresponding to the 82Hz response. The contour lines showed a rapid change in the phases ecorded near the cochlear nucleus. These findings suggest that the cochlear nucleus contributes to the generation of scalp recorded AMFR at a MF of 80Hz.


  • 日本耳鼻咽喉科學會會報

    日本耳鼻咽喉科學會會報 103(3), 177-187, 2000-03-20

    The Oto-Rhino-Laryngological Society of Japan, Inc.

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