THE EXPERIMENTAL FOUNDATIONS FOR NEW TESTS OF VESTIBULAR FUNCTION

Ian S CURTHOYS

Department of Psychology, University of Sydney, Nsw, Australia

Extracellular single neuron recordings from primary otolith and semicircular canal afferents in guinea pigs are providing evidence about how new clinical tests of otolith function work, but also how semicircular canal dehiscence (SCD) affects canal and otolith receptors. Afferents from the anterior canal with irregular resting discharge are not activated by sound (up to 135 dB SPL) or vibration in healthy guinea pigs with normally encased bony labyrinths. However, if an SCD is made then the same semicircular canal neuron which was insensitive to sound or vibration before SCD now shows sensitive phase-locked activity for air-conducted sound up to >3000Hz. In light of evidence and modelling by Rosowski and others we suggest that the reason for this is that the SCD enhances fluid displacement and so canal (and otolith) neurons show phase-locked responses and lowered thresholds. Maintained high frequency stimulation elicits a sustained change in firing in anterior canal neurons. In some cases that appears due to maintained phase locking activating the cell on each cycle, since the activation ceases abruptly at stimulus offset. In other cases the sound appears to cause a maintained fluid displacement, by virtue of the sound causing a deflection of the cupula since it takes seconds (a cupula time constant) after stimulus offset to return to resting activity. This may be caused by sound inducing an “impedance pump” which deflects the cupula. These neural results appear to explain both the enhanced VEMP responses after SCD and the maintained nystagmus (Tullio phenomenon) to maintained sound stimulation.

PL09

前庭功能檢查新技術(shù)的實(shí)驗(yàn)基礎(chǔ)

Ian S CURTHOYS

澳大利亞，新南威爾士,，悉尼大學(xué),，心理學(xué)院 

豚鼠的初級(jí)耳石和半規(guī)管傳入神經(jīng)的細(xì)胞外單神經(jīng)元記錄，不但提供了新的耳石功能檢測(cè)方法,，而且提供了半規(guī)管裂（SCD）如何影響半規(guī)管和耳石感受器的證據(jù),。在骨迷路正常的健康豚鼠中，聲音刺激（最大至135dB SPL）或振動(dòng)不能刺激前半規(guī)管傳入神經(jīng)的不規(guī)則放電,。但是,，若制作一個(gè)半規(guī)管裂的動(dòng)物模型，使之前對(duì)聲音及振動(dòng)不敏感的前半規(guī)管神經(jīng)元對(duì)頻率最大到3000Hz的氣導(dǎo)聲音有鎖相反應(yīng),。依據(jù)Rosowski等制作的模型以及現(xiàn)有證據(jù),，我們認(rèn)為此現(xiàn)象的原因是SCD增加了液體的流動(dòng)性，使半規(guī)管（及耳石）神經(jīng)元呈現(xiàn)相位鎖定響應(yīng)及低閾值,。持續(xù)的高頻刺激,，使前半規(guī)管神經(jīng)元的放電狀態(tài)持續(xù)改變。在一些情況下,，該現(xiàn)象出現(xiàn)是因?yàn)榧?xì)胞周期中需要維持鎖相激活,，當(dāng)刺激結(jié)束后激活狀態(tài)立刻停止。另一種情況下,，在刺激結(jié)束后神經(jīng)元需要數(shù)秒（壺腹帽時(shí)間常數(shù)）才能回到靜息狀態(tài),，聲音可能引起持續(xù)的液體移位，后者導(dǎo)致壺腹帽的偏移,。這或許是因?yàn)槁曇粽T發(fā)產(chǎn)生了類似“阻抗泵”的作用,，引起壺腹帽偏移。這些神經(jīng)活動(dòng)的結(jié)果可以解釋出SCD后VEMP反應(yīng)增強(qiáng),，以及持續(xù)聲音刺激引起的持續(xù)性眼震（Tullio現(xiàn)象）,。

（畢競(jìng)韜 譯，劉博 校,，首都醫(yī)科大學(xué)附屬北京同仁醫(yī)院耳鼻咽喉頭頸外科）