Santarelli R, Maurizi M, Conti G, Ottaviani F, Paludetti G, Pettorossi V E
Institute of Human Physiology, Rome, Italy.
Hear Res. 1995 Mar;83(1-2):9-18. doi: 10.1016/0378-5955(94)00185-s.
In order to investigate the generation of the 40 Hz steady-state response (SSR), auditory potentials evoked by clicks were recorded in 16 healthy subjects in two stimulating conditions. Firstly, repetition rates of 7.9 and 40 Hz were used to obtain individual middle latency responses (MLRs) and 40 Hz-SSRs, respectively. In the second condition, eight click trains were presented at a 40 Hz repetition rate and an inter-train interval of 126 ms. We extracted from the whole train response: (1) the response-segment taking place after the last click of the train (last click response, LCR), (2) a modified LCR (mLCR) obtained by clearing the LCR from the amplitude enhancement due to the overlapping of the responses to the clicks preceding the last within the stimulus train. In comparison to MLRs, the most relevant feature of the evoked activity following the last click of the train (LCRs, mLCRs) was the appearance in the 50-110 ms latency range of one (in 11 subjects) or two (in 2 subjects) additional positive-negative deflections having the same periodicity as that of MLR waves. The grand average (GA) of the 40 Hz-SSRs was compared with three predictions synthesized by superimposing: (1) the GA of MLRs, (2) the GA of LCRs, (3) the GA of mLCRs. Both the MLR and mLCR predictions reproduced the recorded signal in amplitude while the LCR prediction amplitude resulted almost twice that of the 40 Hz-SSR. With regard to the phase, the MLR, LCR and mLCR closely predicted the recorded signal. Our findings confirm the effectiveness of the linear addition mechanism in the generation of the 40 Hz-SSR. However the responses to individual stimuli within the 40 Hz-SSR differ from MLRs because of additional periodic activity. These results suggest that phenomena related to the resonant frequency of the activated system may play a role in the mechanisms which interact to generate the 40 Hz-SSR.
为了研究40Hz稳态反应（SSR）的产生，在两种刺激条件下记录了16名健康受试者的点击诱发听觉电位。首先，分别使用7.9Hz和40Hz的重复率来获取个体中潜伏期反应（MLR）和40Hz-SSR。在第二种条件下，以40Hz的重复率和126ms的串间间隔呈现八组点击序列。我们从整个序列反应中提取：（1）序列中最后一次点击后出现的反应片段（最后一次点击反应，LCR），（2）通过消除由于刺激序列中最后一次点击之前的点击反应重叠导致的振幅增强而获得的改良LCR（mLCR）。与MLR相比，序列中最后一次点击后诱发活动的最相关特征（LCR、mLCR）是在50-110ms潜伏期范围内出现一个（11名受试者）或两个（2名受试者）额外的正负偏转波，其具有与MLR波相同的周期性。将40Hz-SSR的总体平均值（GA）与通过叠加合成的三个预测值进行比较：（1）MLR的GA，（2）LCR的GA，（3）mLCR的GA。MLR和mLCR预测值在振幅上再现了记录信号，而LCR预测值的振幅几乎是40Hz-SSR的两倍。在相位方面，MLR、LCR和mLCR与记录信号密切相符。我们的研究结果证实了线性相加机制在40Hz-SSR产生中的有效性。然而，由于额外的周期性活动，40Hz-SSR中对单个刺激的反应与MLR不同。这些结果表明，与激活系统的共振频率相关的现象可能在相互作用产生40Hz-SSR的机制中起作用。
