Qin Ling, Sakai Masashi, Chimoto Sohei, Sato Yu
Department of Physiology, Interdisciplinary Graduate School of Medicine and Engineering University of Yamanashi Tamaho, Yamanashi, 409-3898, Japan.
Brain Res. 2004 Jul 16;1014(1-2):1-13. doi: 10.1016/j.brainres.2004.03.072.
Although psychophysical studies have revealed involvement of spectral edges in auditory perception, little is known about neural processing. This study investigates how spectral edges are processed in neurons of alert cat primary-auditory-cortex (A1) with sustained response property. Stimuli are low-pass, high-pass and band-pass tones with sharp spectral edges whose edge-frequencies were systematically shifted, constructing edge-frequency response functions. Pure- and two-tone stimuli served to delineate excitatory and inhibitory subfields of the frequency response field (FRF). Based on the response function characteristics, cells were divided into edge-sensitive and edge-insensitive cells: the edge sensitive cells had narrow tuning to the high-edge (type-II cells) or low-edge (type-III cells) frequencies, while the edge insensitive cells were driven by any static stimuli with energy on FRF (type-I) or only very narrowband stimuli with energy confined to FRF (type-IV cells). Edge-sensitive cells showed a close correlation between the best frequencies of the single-frequency (BFSF) and edge-frequency (BFEF) response functions and between their half-height bandwidths, suggesting that the edge-frequency identification is processed along the tonotopic axis in A1. BFSF shifted (mean 0.11 octaves) into the stimulus band from the BFEF (closely corresponding to pitch shift into stimulus band from the edge frequency in human psychophysical data of edge-pitch), suggesting central mechanism of edge-pitch sensation. Type-I cells had non-significant inhibitory subfields of FRF; type-II cells had the significant inhibitory subfield on the higher frequency side; type-III cells, on the lower frequency side; and type-IV cells, on both sides, suggesting that the inhibitory mechanism characterizes the cell-type specific spectral-edge sensitivity.
尽管心理物理学研究已经揭示了频谱边缘在听觉感知中的作用，但对于神经处理过程却知之甚少。本研究调查了警觉猫初级听觉皮层（A1）中具有持续反应特性的神经元如何处理频谱边缘。刺激为具有尖锐频谱边缘的低通、高通和带通音调，其边缘频率被系统地改变，构建边缘频率响应函数。纯音和双音刺激用于描绘频率响应场（FRF）的兴奋性和抑制性子场。根据响应函数特征，细胞被分为边缘敏感细胞和边缘不敏感细胞：边缘敏感细胞对高频边缘（II型细胞）或低频边缘（III型细胞）频率具有窄调谐，而边缘不敏感细胞由FRF上有能量的任何静态刺激驱动（I型）或仅由能量局限于FRF的非常窄带刺激驱动（IV型细胞）。边缘敏感细胞在单频率（BFSF）和边缘频率（BFEF）响应函数的最佳频率之间以及它们的半高带宽之间显示出密切相关性，这表明边缘频率识别是沿着A1中的音频拓扑轴进行处理的。BFSF从BFEF移入刺激频段（平均0.11倍频程）（与人类心理物理学边缘音高数据中边缘频率移入刺激频段时的音高变化密切对应），表明边缘音高感觉的中枢机制。I型细胞的FRF具有不显著的抑制性子场；II型细胞在较高频率侧具有显著的抑制性子场；III型细胞在较低频率侧具有显著的抑制性子场；IV型细胞在两侧都具有显著的抑制性子场，这表明抑制机制表征了细胞类型特异性的频谱边缘敏感性。
