Lu T, Wang X
Laboratory of Auditory Neurophysiology, Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
J Neurophysiol. 2000 Jul;84(1):236-46. doi: 10.1152/jn.2000.84.1.236.
The present study investigated neural responses to rapid, repetitive stimuli in the primary auditory cortex (A1) of cats. We focused on two important issues regarding cortical coding of sequences of stimuli: temporal discharge patterns of A1 neurons as a function of inter-stimulus interval and cortical mechanisms for representing successive stimulus events separated by very short intervals. These issues were studied using wide- and narrowband click trains with inter-click intervals (ICIs) ranging from 3 to 100 ms as a class of representative sequential stimuli. The main findings of this study are 1) A1 units displayed, in response to click train stimuli, three distinct temporal discharge patterns that we classify as regions I, II, and III. At long ICIs nearly all A1 units exhibited typical stimulus-synchronized response patterns (region I) consistent with previously reported observations. At intermediate ICIs, no clear temporal structures were visible in the responses of most A1 units (region II). At short ICIs, temporal discharge patterns are characterized by the presence of either intrinsic oscillations (at approximately 10 Hz) or a change in discharge rate that was a monotonically decreasing function of ICI (region III). In some A1 units, temporal discharge patterns corresponding to region III were absent. 2) The boundary between regions I and II (synchronization boundary) had a median value of 39.8 ms ICI ([25%, 75%] = [20.4, 58. 8] ms ICI; n = 131). The median boundary between regions II and III was estimated at 6.3 ms ([25%, 75%] = [5.2, 9.7] ms ICI; n = 47) for units showing rate changes (rate-change boundary). 3) The boundary values between different regions appeared to be relatively independent of stimulus intensity (at modest sound levels) or the bandwidth of the clicks used. 4) There is a weak correlation between a unit's synchronization boundary and its response latency. Units with shorter latencies appeared to also have smaller boundary values. And 5) based on these findings, we proposed a two-stage model for A1 neurons to represent a wide range of ICIs. In this model, A1 uses a temporal code for explicitly representing long ICIs and a rate code for implicitly representing short ICIs.
本研究调查了猫初级听觉皮层（A1）对快速、重复刺激的神经反应。我们关注了关于刺激序列皮层编码的两个重要问题：A1神经元的时间放电模式作为刺激间隔的函数，以及用于表征由非常短的间隔分隔的连续刺激事件的皮层机制。使用点击间隔（ICI）范围为3至100毫秒的宽带和窄带点击序列作为一类代表性的序列刺激来研究这些问题。本研究的主要发现如下：1）A1神经元对点击序列刺激表现出三种不同的时间放电模式，我们将其分类为I、II和III区。在长ICI时，几乎所有A1神经元都表现出与先前报道的观察结果一致的典型刺激同步反应模式（I区）。在中等ICI时，大多数A1神经元的反应中没有明显的时间结构（II区）。在短ICI时,时间放电模式的特征是存在固有振荡（约10赫兹）或放电率变化，该变化是ICI的单调递减函数（III区）。在一些A1神经元中，不存在对应于III区的时间放电模式。2）I区和II区之间的边界（同步边界）的ICI中位数为39.8毫秒（[25%，75%]=[20.4，58.8]毫秒ICI；n = 131）。对于表现出速率变化的神经元（速率变化边界），II区和III区之间的中位数边界估计为6.3毫秒（[25%，75%]=[5.2，9.7]毫秒ICI；n = 47）。3）不同区域之间的边界值似乎相对独立于刺激强度（在适度的声级下）或所用点击的带宽。4）神经元的同步边界与其反应潜伏期之间存在弱相关性。潜伏期较短神经元的边界值似乎也较小。5）基于这些发现，我们提出了一个两阶段模型，用于A1神经元表征广泛的ICI范围。在这个模型中，A1使用时间编码来明确表征长ICI，使用速率编码来隐含表征短ICI。
