Institute for Biomagnetism and Biosignalanalysis, University Hospital, Münster, Germany.
Department of Integrative Physiology, National Institute for Physiological Sciences, Okazaki, Japan.
PLoS One. 2013 Dec 9;8(12):e80899. doi: 10.1371/journal.pone.0080899. eCollection 2013.
We investigated the modulation of lateral inhibition in the human auditory cortex by means of magnetoencephalography (MEG). In the first experiment, five acoustic masking stimuli (MS), consisting of noise passing through a digital notch filter which was centered at 1 kHz, were presented. The spectral energy contrasts of four MS were modified systematically by either amplifying or attenuating the edge-frequency bands around the notch (EFB) by 30 dB. Additionally, the width of EFB amplification/attenuation was varied (3/8 or 7/8 octave on each side of the notch). N1m and auditory steady state responses (ASSR), evoked by a test stimulus with a carrier frequency of 1 kHz, were evaluated. A consistent dependence of N1m responses upon the preceding MS was observed. The minimal N1m source strength was found in the narrowest amplified EFB condition, representing pronounced lateral inhibition of neurons with characteristic frequencies corresponding to the center frequency of the notch (NOTCH CF) in secondary auditory cortical areas. We tested in a second experiment whether an even narrower bandwidth of EFB amplification would result in further enhanced lateral inhibition of the NOTCH CF. Here three MS were presented, two of which were modified by amplifying 1/8 or 1/24 octave EFB width around the notch. We found that N1m responses were again significantly smaller in both amplified EFB conditions as compared to the NFN condition. To our knowledge, this is the first study demonstrating that the energy and width of the EFB around the notch modulate lateral inhibition in human secondary auditory cortical areas. Because it is assumed that chronic tinnitus is caused by a lack of lateral inhibition, these new insights could be used as a tool for further improvement of tinnitus treatments focusing on the lateral inhibition of neurons corresponding to the tinnitus frequency, such as the tailor-made notched music training.
我们利用脑磁图（MEG）研究了人类听觉皮层中侧抑制的调制。在第一个实验中，呈现了五个声学掩蔽刺激（MS），由通过数字陷波滤波器的噪声组成，该滤波器的中心频率为 1 kHz。通过将陷波（EFB）边缘频带的频谱能量对比度放大或衰减 30 dB，系统地改变了四个 MS 的能量对比度。此外，还改变了 EFB 放大/衰减的宽度（陷波两侧各为 3/8 或 7/8 倍频程）。评估了中心频率为 1 kHz 的测试刺激诱发的 N1m 和听觉稳态反应（ASSR）。观察到 N1m 反应与先前的 MS 之间存在一致的依赖性。在最窄的放大 EFB 条件下，发现最小的 N1m 源强度，这代表了在次级听觉皮层区域中与陷波中心频率（NOTCH CF）相对应的神经元的明显侧抑制。在第二个实验中，我们测试了更窄的 EFB 放大带宽是否会导致 NOTCH CF 的侧抑制进一步增强。这里呈现了三个 MS，其中两个通过放大陷波周围的 1/8 或 1/24 倍频程 EFB 宽度来修改。我们发现，与 NFN 条件相比，在这两种放大 EFB 条件下，N1m 反应再次显著减小。据我们所知，这是首次证明陷波周围 EFB 的能量和宽度调节人类次级听觉皮层区域侧抑制的研究。因为假设慢性耳鸣是由于侧抑制缺乏引起的，这些新的见解可以用作进一步改善针对耳鸣频率（如定制缺口音乐训练）神经元侧抑制的耳鸣治疗的工具。
