持续性听觉诱发电位频谱特性的分析研究

FREQUENCY NONLINEARITY IN SUSTAINEDAUDITORY EVOKED POTENTIALS

本文从理论上研究了等间隔重复脉冲刺激下持续反应中的稳态反应与其中单个脉冲在其它脉冲作用下引起的反应,提出了它们在频率域上相互关系的公式。并在耳蜗电位和脑干听觉诱发电位中验证了这一公式的合理性。

<ABSTRACT> In this paper, properties of responses to periodic stimuli of somc biologlcal systems was studied, in which the sustained response could reach steady state if the duration of the stimulus is long enough. It was shown that the steady statc component of the sustained response fu (t ) could be expressed by the summation of the waveforms obtained by shifting a fully masked response to a single cycle un (t ) within the sti- mulus with intervals equal to the integer times of the cycle. It has be- en pointed out that the spectra of fn (t ) and un (t ) could be correlated Fn(ω)=Un(ω)sin(n+1)ωT/sinωT, with the following formula: Fn(ω) = Um(ω)sin(n+1)ωT/sinωT, where T stands for the cycle of the stimulus.From this formula, it was deduced that there would be peaks in the spectrum of the steady state response as the frequencies equaled to the integer times of the frequency of the stimulus; the higher the frequency of the stimulus, the less wo- uld be the harmonic componcnts; and the frequency range of the steady state response was restricted by the frequency pass band of Un(ω). These conclusions were tested and verified in cochlea potentials and br- ainstem auditory potentials, the cochlca potentials being recorded from the round window of inner ear of guinea pigs and the brainstem audit- ory potentials from the scalp. A comparison of the theoretical expectant and experimental results was also made quantitatively. The well fitting result was a strong support to our theory and gave a reasonable explan- ation to the 'frequency following' mechanism and the frequency nonlih- earity phenomenon in biological systems, which was rather general for evoked potentials. Besides, a possible explaination was also given for the frequency limitation of auditory frequency following responses.