Kaltenbach J A, Meleca R J, Falzarano P R, Myers S F, Simpson T H
Department of Audiology, Wayne State University, School of Medicine, Detroit, Michigan 48201.
Hear Res. 1993 May;67(1-2):35-44. doi: 10.1016/0378-5955(93)90229-t.
The majority of single unit studies in the auditory system have been carried out using stimuli whose temporal and spectral contexts are held constant. Relatively little attention has been given to the influence of context on unit response properties. Indeed, auditory nerve fiber responses are known to be context-dependent due to the property of forward masking, a phenomenon by which the response to one sound results in a reduction in the response to a subsequent sound. Forward masking might be expected to be even more influential at central levels of the auditory pathway where the responses are reshaped by additional synaptic interactions. The purpose of the present study was to characterize the forward masking properties of neurons in the dorsal cochlear nucleus (DCN). A tool was developed for measuring the response to a probe tone as a function of delay following a previous tone-burst. The frequency of the probe was held constant at the unit's characteristic frequency while the frequency of the leading tone (masker) was varied. These measures provided a description of neural masking effects in different temporal and spectral contexts. The data yielded two patterns of suppression. In the first pattern (Type A), the suppression of the probe response became evident immediately following offset of the masker; the suppression bandwidth showed a gradual narrowing as the delay between masker and probe was increased. In the second class (Type B), the suppression of the probe response did not become evident until well after offset of the masker; this pattern appeared more circumscribed in that the suppression bandwidth gradually increased as a function of delay up to a maximum then decreased with further increases in delay. The results imply that mechanisms intrinsic to the DCN contribute to further modification and reshaping of the spectral and temporal context of masking effects beyond those seen in the auditory nerve. It is hypothesized that such properties may be specialized for suppressing the response to echoes thus facilitating communication and localization of sound in enclosed spaces.
听觉系统中大多数单单元研究都是使用时间和频谱背景保持恒定的刺激进行的。相对而言，很少有人关注背景对单元反应特性的影响。实际上，由于前掩蔽特性，听神经纤维反应已知是依赖于背景的，前掩蔽是一种现象，即对一个声音的反应会导致对后续声音的反应减少。在前掩蔽在听觉通路的中枢水平可能更具影响力，在那里反应会通过额外的突触相互作用而重塑。本研究的目的是表征背侧耳蜗核（DCN）中神经元的前掩蔽特性。开发了一种工具，用于测量在先前的短纯音之后作为延迟函数的对探测音的反应。探测音的频率在单元的特征频率处保持恒定，而先导音（掩蔽音）的频率则变化。这些测量提供了在不同时间和频谱背景下神经掩蔽效应的描述。数据产生了两种抑制模式。在第一种模式（A 型）中，掩蔽音消失后立即出现对探测反应的抑制；随着掩蔽音和探测音之间的延迟增加，抑制带宽逐渐变窄。在第二类（B 型）中，对探测反应的抑制直到掩蔽音消失后很久才变得明显；这种模式似乎更具局限性，因为抑制带宽随着延迟增加到最大值然后随着延迟进一步增加而减小。结果表明，DCN 的内在机制有助于对掩蔽效应的频谱和时间背景进行进一步的修改和重塑，超出了听神经中的情况。据推测，这些特性可能专门用于抑制对回声的反应，从而促进在封闭空间中声音的通信和定位。
