Calford M B, Rajan R, Irvine D R
Department of Psychology, Monash University, Clayton, Victoria, Australia.
Neuroscience. 1993 Aug;55(4):953-64. doi: 10.1016/0306-4522(93)90310-c.
The response areas (frequency by intensity) of single neurons in primary auditory cortex of anesthetized cats were studied before and after temporary threshold shifts in cochlear sensitivity induced by an intense pure tone. Cochlear temporary threshold shift was monitored through the threshold of the gross auditory nerve compound action potential and in most cases involved a notch-like loss centered at the characteristic frequency of the unit under study. Only two neurons showed changes in response area that mirrored the changes at the auditory periphery. Most neurons (14) showed more complex changes involving both expansion and contraction of response areas. Expansion of response areas was indicated by lower thresholds at some frequencies and by the emergence of sensitivity to previously ineffective frequencies. A change was classified as contraction when the response area after the intense-tone exposure was smaller than would be expected by applying the profile of the temporary threshold shift to the initial response area. Contraction of both upper (high intensity) and lower boundaries of response areas was found; in the most extreme cases, neurons were totally unresponsive after the intense-tone exposure. The complexity of effects of temporary threshold shifts on the response areas of cortical neurons is likely to be related to mechanisms that normally determine the frequency response limits of these neurons. The response areas of cortical neurons are more complex than those of auditory nerve fibers, and are thought to reflect the integration of excitatory and inhibitory inputs. The variety of effects observed in this study are consistent with the excitatory and inhibitory components of the response area of a given neuron being differentially affected by the temporary threshold shift.
在由强纯音引起的耳蜗敏感性暂时阈移前后，对麻醉猫初级听觉皮层单个神经元的反应区域（频率与强度的关系）进行了研究。通过总听神经复合动作电位的阈值监测耳蜗暂时阈移，在大多数情况下，其涉及以所研究单元的特征频率为中心的类似凹口的损失。只有两个神经元的反应区域变化反映了听觉外周的变化。大多数神经元（14个）表现出更复杂的变化，包括反应区域的扩张和收缩。反应区域的扩张表现为某些频率下阈值降低以及对先前无效频率出现敏感性。当强音暴露后的反应区域小于将暂时阈移曲线应用于初始反应区域所预期的大小时，变化被归类为收缩。发现反应区域的上边界（高强度）和下边界都有收缩；在最极端的情况下，强音暴露后神经元完全无反应。耳蜗暂时阈移对皮层神经元反应区域的影响复杂性可能与通常决定这些神经元频率反应极限的机制有关。皮层神经元的反应区域比听神经纤维的更复杂，并且被认为反映了兴奋性和抑制性输入的整合。本研究中观察到的各种效应与给定神经元反应区域的兴奋性和抑制性成分受到暂时阈移的不同影响是一致的。
