School of Psychological and Cognitive Sciences, Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing, 100080, China.
School of Psychological and Cognitive Sciences, Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing, 100080, China; Beijing Key Laboratory of Epilepsy, Epilepsy Center, Department of Functional Neurosurgery, Sanbo Brain Hospital, Capital Medical University, Beijing, 100093, China.
Hear Res. 2019 Jun;377:224-233. doi: 10.1016/j.heares.2019.04.003. Epub 2019 Apr 8.
Accurate neural representations of acoustic signals under noisy conditions are critical for animals' survival. Detecting signal against background noise can be improved by binaural hearing particularly when an interaural-time-difference (ITD) disparity is introduced between the signal and the noise, a phenomenon known as binaural unmasking. Previous studies have mainly focused on the binaural unmasking effect on response magnitudes, and it is not clear whether binaural unmasking affects the accuracy of central representations of target acoustic signals and the relative contributions of different central auditory structures to this accuracy. Frequency following responses (FFRs), which are sustained phase-locked neural activities, can be used for measuring the accuracy of the representation of signals. Using intracranial recordings of local field potentials, this study aimed to assess whether the binaural unmasking effects include an improvement of the accuracy of neural representations of sound-envelope signals in the rat IC and/or auditory cortex (AC). The results showed that (1) when a narrow-band noise was presented binaurally, the stimulus-response (S-R) coherence of the FFRs to the envelope (FFR) of the narrow-band noise recorded in the IC was higher than that recorded in the AC. (2) Presenting a broad-band masking noise caused a larger reduction of the S-R coherence for FFR in the IC than that in the AC. (3) Introducing an ITD disparity between the narrow-band signal noise and the broad-band masking noise did not affect the IC S-R coherence, but enhanced both the AC S-R coherence and the coherence between the IC FFR and AC FFR. Thus, although the accuracy of representing envelope signals in the AC is lower than that in the IC, it can be binaurally unmasked, indicating a binaural-unmasking mechanism that is formed during the signal transmission from the IC to the AC.
在噪声环境下准确地对声音信号进行神经编码对于动物的生存至关重要。双耳听觉特别有助于在信号和噪声之间引入耳间时间差（ITD）差异时，提高对信号的检测能力，这种现象被称为双耳掩蔽。先前的研究主要集中在双耳掩蔽对反应幅度的影响上，目前尚不清楚双耳掩蔽是否会影响目标声信号的中枢表示的准确性，以及不同中枢听觉结构对这种准确性的相对贡献。频率跟随反应（FFR）是一种持续的相位锁定的神经活动，可以用于测量信号表示的准确性。本研究使用颅内局部场电位记录来评估双耳掩蔽效应是否包括改善大鼠听皮层（IC）和/或听觉皮层（AC）中声音包络信号的神经表示的准确性。结果表明：（1）当窄带噪声以双耳方式呈现时，IC 中记录的窄带噪声包络（FFR）的刺激-反应（S-R）相干性高于 AC 中记录的相干性。（2）呈现宽带掩蔽噪声会导致 IC 中 FFR 的 S-R 相干性比 AC 中更大的降低。（3）在窄带信号噪声和宽带掩蔽噪声之间引入 ITD 差异不会影响 IC 的 S-R 相干性，但会增强 AC 的 S-R 相干性和 IC FFR 与 AC FFR 之间的相干性。因此，尽管 AC 中表示包络信号的准确性低于 IC，但它可以被双耳掩蔽，这表明在信号从 IC 传输到 AC 的过程中形成了一种双耳掩蔽机制。
