Calcus Axelle, Undurraga Jaime A, Vickers Deborah
Department of Speech, Hearing and Phonetic Sciences, University College London, London, United Kingdom.
Laboratoire des Systèmes Perceptifs, Département d'Etudes Cognitives, Ecole Normale Supérieure, PSL University, CNRS, Paris, France.
Front Neurol. 2022 Aug 3;13:928158. doi: 10.3389/fneur.2022.928158. eCollection 2022.
Objective assessment of auditory discrimination has often been measured using the Auditory Change Complex (ACC), which is a cortically generated potential elicited by a change occurring within an ongoing, long-duration auditory stimulus. In cochlear implant users, the electrically-evoked ACC has been used to measure electrode discrimination by changing the stimulating electrode during stimulus presentation. In addition to this cortical component, subcortical measures provide further information about early auditory processing in both normal hearing listeners and cochlear implant users. In particular, the frequency-following response (FFR) is thought to reflect the auditory encoding at the level of the brainstem. Interestingly, recent research suggests that it is possible to simultaneously measure both subcortical and cortical physiological activity. The aim of this research was twofold: first, to understand the scope for simultaneously recording both the FFR (subcortical) and ACC (cortical) responses in normal hearing adults. Second, to determine the best recording parameters for optimizing the simultaneous capture of both responses with clinical applications in mind. Electrophysiological responses were recorded in 10 normally-hearing adults while they listened to 16-second-long pure tone sequences. The carrier frequency of these sequences was either steady or alternating periodically throughout the sequence, generating an ACC response to each alternation-the alternating ACC paradigm. In the "alternating" sequences, both the alternating rate and the carrier frequency varied parametrically. We investigated three alternating rates (1, 2.5, and 6.5 Hz) and seven frequency pairs covering the low-, mid-, and high-frequency range, including narrow and wide frequency separations. Our results indicate that both the slowest (1 Hz) and medium (2.5 Hz) alternation rates led to significant FFR and ACC responses in most frequency ranges tested. Low carrier frequencies led to larger FFR amplitudes, larger P1 amplitudes, and N1-P2 amplitude difference at slow alternation rates. No significant relationship was found between subcortical and cortical response amplitudes, in line with different generators and processing levels across the auditory pathway. Overall, the alternating ACC paradigm can be used to measure sub-cortical and cortical responses as indicators of auditory early neural encoding (FFR) and sound discrimination (ACC) in the pathway, and these are best obtained at slow alternation rates (1 Hz) in the low-frequency range (300-1200 Hz).
听觉辨别能力的客观评估通常使用听觉变化复合体（ACC）来测量，ACC是一种由持续的长时间听觉刺激中的变化所引发的皮层诱发电位。在人工耳蜗使用者中，电诱发的ACC已被用于通过在刺激呈现过程中改变刺激电极来测量电极辨别能力。除了这种皮层成分外，皮层下测量还能提供有关正常听力者和人工耳蜗使用者早期听觉处理的更多信息。特别是，频率跟随反应（FFR）被认为反映了脑干水平的听觉编码。有趣的是，最近的研究表明，可以同时测量皮层下和皮层的生理活动。本研究的目的有两个：第一，了解在正常听力成年人中同时记录FFR（皮层下）和ACC（皮层）反应的可能性。第二，确定在考虑临床应用的情况下，用于优化同时捕捉这两种反应的最佳记录参数。在10名正常听力的成年人听16秒长的纯音序列时记录其电生理反应。这些序列的载波频率在整个序列中要么保持稳定，要么周期性交替，每次交替都会产生一个ACC反应——交替ACC范式。在“交替”序列中，交替速率和载波频率都进行了参数化变化。我们研究了三种交替速率（1、2.5和6.5赫兹）以及七对覆盖低、中、高频范围的频率对，包括窄频率间隔和宽频率间隔。我们的结果表明，在大多数测试频率范围内，最慢的（1赫兹）和中等的（2.5赫兹）交替速率都能引发显著的FFR和ACC反应。在缓慢交替速率下，低载波频率会导致更大的FFR振幅、更大的P1振幅以及N1 - P2振幅差。皮层下和皮层反应振幅之间未发现显著关系，这与听觉通路中不同的发生器和处理水平一致。总体而言，交替ACC范式可用于测量皮层下和皮层反应，作为听觉早期神经编码（FFR）和通路中声音辨别（ACC）的指标，并且在低频范围（300 - 1200赫兹）以缓慢交替速率（1赫兹）时能最好地获得这些指标。
