Liu R C, Tzonev S, Rebrik S, Miller K D
Keck Center for Integrative Neuroscience and Department of Physiology, University of California, San Francisco, California 94143-0444, USA.
J Neurophysiol. 2001 Dec;86(6):2789-806. doi: 10.1152/jn.2001.86.6.2789.
A central theme in neural coding concerns the role of response variability and noise in determining the information transmission of neurons. This issue was investigated in single cells of the lateral geniculate nucleus of barbiturate-anesthetized cats by quantifying the degree of precision in and the information transmission properties of individual spike train responses to full field, binary (bright or dark), flashing stimuli. We found that neuronal responses could be highly reproducible in their spike timing (approximately 1-2 ms standard deviation) and spike count (approximately 0.3 ratio of variance/mean, compared with 1.0 expected for a Poisson process). This degree of precision only became apparent when an adequate length of the stimulus sequence was specified to determine the neural response, emphasizing that the variables relevant to a cell's response must be controlled to observe the cell's intrinsic response precision. Responses could carry as much as 3.5 bits/spike of information about the stimulus, a rate that was within a factor of two of the limit the spike train could transmit. Moreover, there appeared to be little sign of redundancy in coding: on average, longer response sequences carried at least as much information about the stimulus as would be obtained by adding together the information carried by shorter response sequences considered independently. There also was no direct evidence found for synergy between response sequences. These results could largely, but not entirely, be explained by a simple model of the response in which one filters the stimulus by the cell's impulse response kernel, thresholds the result at a fairly high level, and incorporates a postspike refractory period.
神经编码中的一个核心主题涉及反应变异性和噪声在决定神经元信息传递方面的作用。通过量化单个神经元对全场二元（亮或暗）闪烁刺激的尖峰序列反应的精确程度和信息传递特性，对巴比妥麻醉猫的外侧膝状核单细胞进行了此项研究。我们发现，神经元反应在其尖峰时间（标准差约为1 - 2毫秒）和尖峰计数（方差/均值约为0.3，而泊松过程预期为1.0）方面具有高度可重复性。只有当指定足够长的刺激序列来确定神经反应时，这种精确程度才会显现出来，这强调了必须控制与细胞反应相关的变量，以观察细胞的固有反应精度。反应能够携带多达3.5比特/尖峰的关于刺激的信息，这一速率在尖峰序列能够传输的极限的两倍范围内。此外，编码中似乎几乎没有冗余迹象：平均而言，较长的反应序列携带的关于刺激的信息至少与独立考虑的较短反应序列携带的信息相加所获得的信息一样多。也没有直接证据表明反应序列之间存在协同作用。这些结果在很大程度上，但并非完全可以由一个简单的反应模型来解释，在该模型中，通过细胞的脉冲响应内核过滤刺激，在相当高的水平对结果进行阈值处理，并纳入尖峰后的不应期。
