MRC Cognition and Brain Sciences Unit, Cambridge, UK.
Adv Exp Med Biol. 2013;787:231-8. doi: 10.1007/978-1-4614-1590-9_26.
Neurons sensitive to interaural time differences (ITDs) in the fine structure of low-frequency signals have been found in binaurally responsive auditory nuclei in a wide range of species. The present study investigated whether the frequency following response (FFR) would show evidence for neurons “tuned” to ITD in humans. The FFR is a scalp-recorded measure of sustained phase-locked brainstem activity that has been shown to follow the frequency of low-frequency tones. The magnitude of the FFR often decreases over time for tones of long duration. The present study investigated whether this adaptation effect is ITD specific.The FFR to a 100-ms, 80-dB SPL, 504-Hz target tone was measured for ten subjects. The target was preceded by a 200-ms, 80-dB SPL, 504-Hz adaptor. The target always led by 0.5 ms in the left ear. The adaptor led either in the left ear or in the right ear by 0.5 ms. Stimuli (adaptor + target = pair) were presented in alternating polarity at a rate of 1.81 Hz. We used a “vertical” montage (+Fz, – C7, ground = Fpz) for which the FFR is assumed to reflect phase-locked neural activity from rostral generators in the brainstem. The averaged FFR waveforms for each polarity were subtracted, to enhance temporal fine structure responses. The results showed significant adaptation effects in the spectral magnitude of the FFR. However, adaptation was not larger when the adaptor had the same ITD as the target than when the ITD of the adaptor differed from that of the target. Thus, the current data provide no evidence that the spectral magnitude of the scalp-recorded FFR provides a non-invasive indicator of ITD-specific neural activation.
已在多种物种的双侧反应性听觉核中发现了对低频信号精细结构中的两耳时间差 (ITD) 敏感的神经元。本研究旨在探讨频率跟随反应 (FFR) 是否会为人类对 ITD 进行“调谐”的神经元提供证据。FFR 是一种头皮记录的脑桥持续相位锁定活动的测量方法，已被证明可跟随低频音调的频率。对于长时间的音调，FFR 的幅度通常会随时间而降低。本研究探讨了这种适应效应是否具有 ITD 特异性。
本研究对 10 名受试者进行了 100ms、80dB SPL、504Hz 目标音的 FFR 测量。目标音之前是 200ms、80dB SPL、504Hz 的适应音。目标音总是在左耳领先 0.5ms。适应音在左耳或右耳领先 0.5ms。刺激（适应音+目标音=一对）以 1.81Hz 的速率交替极性呈现。我们使用了“垂直”导联 (+Fz，– C7，ground = Fpz)，其中 FFR 被认为反映了来自脑干中颅顶发生器的相位锁定神经活动。为了增强时间精细结构反应，对每个极性的平均 FFR 波形进行了相减。结果表明，FFR 的频谱幅度存在显著的适应效应。然而，当适应音与目标音具有相同的 ITD 时，适应效果并不大于适应音的 ITD 与目标音的 ITD 不同时的适应效果。因此，目前的数据没有提供证据表明头皮记录的 FFR 的频谱幅度提供了 ITD 特异性神经激活的非侵入性指标。
