Hoke M, Pantev C, Lütkenhöner B, Lehnertz K
Institute of Experimental Audiology, University of Münster, Germany.
Acta Otolaryngol Suppl. 1991;491:176-81; discussion 182. doi: 10.3109/00016489109136796.
The waveforms of the auditory evoked magnetic field (AEF) in normal-hearing individuals and patients suffering from tinnitus are distinctly different. In tinnitus patients, the magnetic wave M200 (corresponding to the electric wave P200, or P2) is delayed and only poorly developed or even completely missing, while the amplitude of the magnetic wave M100 (corresponding to the electric wave N100, or N1) is significantly augmented. A very characteristic feature turned out to be the amplitude ratio of the two waves M200 and M100. Below the age of 50, the amplitude ratio M200/M100 represents a clear-cut criterion to distinguish between tinnitus patients and individuals without tinnitus. In tinnitus patients, the ratio is less than 0.5 independent of age, whereas, in young and middle-aged normal-hearing individuals, it is greater than 0.5. Since in normal-hearing individuals the average amplitude ratio decreases linearly with age, the clusters of amplitude ratios of the two groups begin to overlap beyond the age of 50. The hypothesis is put forward that the decrease of the average amplitude ratio in normal-hearing individuals reflects a degenerative process probably initiated by multiple exogenous and endogenous factors, which leads to both an increased excitability of the generators of a particular component of wave M100 and a sustained neural activity in the generators of one particular component of wave M200 and eventually gives rise to the sensation of tinnitus. The absence or poor development of wave M200 is a concomitant phenomenon, resulting from the involved generators being less responsive to external stimuli. Our hypothesis has been supported by one exemplary case in which we were able to trace the process of tinnitus remission during a period of 256 days after acute onset of tinnitus (due to an acute noise trauma), showing a recovery of the amplitude ratio from an initial value of 0 to a normal value of approximately 1.
听力正常者与耳鸣患者的听觉诱发磁场（AEF）波形明显不同。在耳鸣患者中，磁波M200（对应于电波P200，即P2）延迟，且仅发育不良甚至完全缺失，而磁波M100（对应于电波N100，即N1）的振幅显著增大。事实证明，M200和M100这两个波的振幅比是一个非常典型的特征。50岁以下，M200/M100振幅比是区分耳鸣患者和无耳鸣个体的明确标准。在耳鸣患者中，该比值与年龄无关均小于0.5，而在中青年听力正常个体中，该比值大于0.5。由于在听力正常个体中，平均振幅比随年龄呈线性下降，两组的振幅比簇在50岁以上开始重叠。有人提出假说，听力正常个体中平均振幅比的下降反映了一个可能由多种外源性和内源性因素引发的退行性过程，这导致M100波特定成分的发生器兴奋性增加以及M200波特定成分的发生器持续神经活动，最终引发耳鸣感觉。M200波的缺失或发育不良是一种伴随现象，是由于相关发生器对外界刺激反应较弱所致。我们的假说得到了一个典型案例的支持，在该案例中，我们能够追踪耳鸣急性发作（由于急性噪声创伤）后256天内的耳鸣缓解过程，结果显示振幅比从初始值0恢复到约1的正常值。
