Auditory cortical onset responses revisited .2. Response strength
Auditory cortical onset responses revisited .2. Response strength
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DOI：
10.1152/jn.1997.77.5.2642
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发表时间：
1997-05-01
影响因子：
2.5
通讯作者：
Heil, P
中科院分区：
文献类型：
--
作者：
Heil, P
听觉通路的大多数神经元会释放与声刺激开始时锁定的尖峰，但声音开始时的声学参数以何种方式塑造神经元反应尚不清楚。本文分析了巴比妥麻醉猫初级听觉皮层中单个神经元在特征频率音调开始时释放的尖峰数量。峰值压力（即包络）的时间进程通过参数变化的声压级 (SPL)、上升时间和上升函数（线性或余弦平方）来改变。对于这两种上升函数，上升时间对常规尖峰计数级别函数、阈值 SPL、动态范围和单调尖峰计数函数饱和的最低 SPL 具有多方面的影响，在某些情况下是显着的，随着上升时间的延长而增加。在大多数具有非单调尖峰计数级函数的神经元中，“最佳 SPL”增加，下降的高 SPL 臂变平，因此通过离子上升时间获得的函数通常是单调的，而通过较短的上升时间获得的函数则高度非单调。因此，对于较长的上升时间音调，SPL 的“调谐”不太尖锐，并且随着 SPL 的增加，尖峰计数与上升时间函数从“短通”变为“长通”。当根据峰值压力的变化率或峰值压力的最大加速度绘制尖峰计数时，上升时间的系统效应仍然存在。然而，当尖峰计数被绘制为响应启动时瞬时峰值压力的函数时，通过不同的上升时间甚至不同的上升函数获得的函数是紧密记录的。这表明第一次尖峰潜伏期的刺激依赖性成分可以被视为积分窗口，在此期间对峰值压力的变化率进行积分。该窗口从音调开始开始，其持续时间与峰值压力的最大加速度（或者，对于线性上升函数，变化率）和神经元的瞬态灵敏度成反比。目前的研究结果严重质疑，对于起始反应，尖峰计数级函数及其衍生的测量的有用性，例如阈值声压级、动态范围、最佳声压级或非单调性程度。他们进一步对当前皮质水平强度编码概念的有效性提出了质疑，因为大多数神经元的起始反应并不代表信号的稳态声压级。然而，他们提出了一种机制，通过这种机制，神经元群体将以有序的、依赖于灵敏度的时间序列对给定的瞬态进行采样。采样率会根据信号变化的速度自动调整。瞬态的瞬时特性可以通过同时活动的子群的响应的比率和空间分布来表示。这种机制可以为快速瞬变的辨别能力提供基础。
Most neurons of the auditory pathway discharge spikes locked to the onset of an acoustic stimulus, but it is largely unknown in which way the acoustic parameters of sound onsets shape the neuronal responses. In this paper is analyzed the number of spikes discharged by single neurons in primary auditory cortex of barbiturate-anesthetized cats to the onsets of tones of characteristic frequency. The time course of the peak pressure (i.e., the envelope) was altered by parametrically varying sound pressure level (SPL), rise time, and rise function (linear or cosine-squared). For both rise functions, rise time had manifold, and in some cases dramatic, effects an conventional spike count-level functions in general, threshold SPL, dynamic range, and the lowest SPL at which monotonic spike count functions saturated increased with prolongation of the rise lime. In neurons with mostly nonmonotonic spike count-level functions, ''best SPL'' increased and the descending high-SPL arms flattened, so that functions obtained with ion rise times were often monotonic whereas those obtained with shorter rise times were highly nonmonotonic. Consequently, the ''tuning'' to SPL was less sharp for longer rise time tones, and spike count versus rise time functions changed from ''short-pass'' to ''long-pass'' with an increase in SPL. Systematic effects of rise time persisted when spike counts were plotted against the rate of change of peak pressure or against the maximum acceleration of peak pressure. However, when spike counts were plotted as a function of the instantaneous peak pressure at the time of response initiation, the functions obtained with different rise times, and even with different rise functions, were in close register. This suggests that the stimulus-dependent component of first-spike latency can be viewed as an integration window, during which rate of change of peak pressure is integrated. The window commences with tone onset and its duration is inversely related to the maximum acceleration( or, for linear rise functions, the rate of change) of peak pressure and the neuron's transient sensitivity. The present findings seriously question, for onset responses, the usefulness of the spike count-level function and measures derived from it, such as threshold SPL, dynamic range, best SPL, or degree of nonmonotonicity. They further cast doubt onto the validity of current concepts of intensity coding at cortical levels, because most neurons' onset responses are not indicative of a signal's steady-state SPL. However, they suggest a mechanism by which a neuronal population will sample a given transient in an orderly, sensitivity-dependent, temporal sequence. The sampling rate is automatically adjusted to, and adjusted by, the rapidity of the signal's change. And the instantaneous properties of the transient could be represented by the ratios and spatial distribution of responses across the simultaneously active subpopulation. Such a mechanism could provide the basis for the demonstrated capability of discrimination of rapid transients.