REPRESENTATION OF SENSORY INFORMATION IN THE CRICKET CERCAL SENSORY SYSTEM .2. INFORMATION THEORETIC CALCULATION OF SYSTEM ACCURACY AND OPTIMAL TUNING-CURVE WIDTHS OF 4 PRIMARY INTERNEURONS
REPRESENTATION OF SENSORY INFORMATION IN THE CRICKET CERCAL SENSORY SYSTEM .2. INFORMATION THEORETIC CALCULATION OF SYSTEM ACCURACY AND OPTIMAL TUNING-CURVE WIDTHS OF 4 PRIMARY INTERNEURONS
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DOI：
10.1152/jn.1991.66.5.1690
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发表时间：
1991-11-01
影响因子：
2.5
通讯作者：
MILLER, JP
中科院分区：
文献类型：
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作者：
THEUNISSEN, FE;MILLER, JP
1.信息论的原理被用来计算板球cercal感觉系统中的风敏感的初级中间神经元的子集所能达到的准确性的极限。对于这些计算，四个神经元的集合被视为一个信息通道，它编码的气流刺激的方向为一个定义的范围内的气流速度。计算的具体信息理论参数是气流方向和神经元尖峰序列之间的“transinformation”或“mutual information”，其特征在前面的报告中。在用于这些计算的假设下，四个中间神经元的集合被证明能够编码4.2到3.5位的风向信息。这对应于4.7度和7.7度的平均定向精度。2.同样的原理被应用于估计调谐曲线宽度的任何变化将影响信息传递的程度。随着模拟调谐曲线宽度的变化，平均系综精度显示出明显的全局最大值。这个最大值对应的调谐曲线宽度为110度宽（在半最大值），这是非常接近的实际平均宽度的调谐曲线中观察到的板球的130度。3.通过一系列的模拟也检查了在刺激范围内的调谐曲线的参数“间距”的变化的效果。允许最大信息传输的配置对应于围绕刺激范围的调谐曲线的相等间隔（即，90-峰值灵敏度点的分离度）。这一理论上的最佳间距与前一份报告中所述实验中观察到的值完全一致。这些模拟还表明，由调谐曲线间距的偏移引起的准确度的降低将取决于方向信息的高阶解码器的可塑性。如果在构成高阶解码器的中间神经元中没有可塑性，那么对于仅3.5度的平均调谐曲线偏移，准确度将降低50%。然而，如果高阶解码网络能够被重新优化到调谐曲线中的任何任意移位，则可达到的准确度的降级将不那么严重，因为高达10度的移位将导致准确度几乎没有降级。从这些结果中，可以得出两个一般性的结论编码的特定刺激参数的阵列的感觉细胞。首先，由具有广泛重叠的调谐曲线的细胞系综对刺激参数进行编码的有效性受到细胞响应的内在方差的严格限制。第二，任何感觉系统对调谐曲线特性变化的鲁棒性都可以通过允许高阶“解码器”网络能够重新优化来大大增强。
1. Principles of information theory were used to calculate the limit of accuracy achievable by a subset of the wind-sensitive primary interneurons in the cricket cercal sensory system. For these calculations, an ensemble of four neurons was treated as an information channel, which encoded the direction of air-current stimuli for a defined range of air-current velocities. The specific information theoretic parameter that was calculated was the "transinformation" or "mutual information" between the air-current directions and the neuronal spike trains, which were characterized in the preceding report. Under the assumptions used for these calculations, the ensemble of four interneurons was demonstrated to be capable of encoding between 4.2 and 3.5 bits of information about wind direction. This corresponds to an average directional accuracy of 4.7 and 7.7-degrees, respectively.2. The same principles were applied to estimate the extent to which any variation in the width of the tuning curves would affect the transfer of information. As the widths of simulated tuning curves were varied, the mean ensemble accuracy showed a clear global maximum. This maximum corresponds to tuning curves widths of 110-degrees wide (at half maximum), which was remarkably close to the actual mean widths of the tuning curves observed in the cricket of 130-degrees.3. The effect of varying the parametric "spacing" of the tuning curves within the stimulus range was also examined through a series of simulations. The configuration allowing the maximum information transfer corresponded to equal spacing of the tuning curves around the stimulus range (i.e., 90-degrees separation of peak sensitivity points). This theoretically optimum spacing corresponded exactly to the values observed in the experiments presented in the preceding report.4. These simulations also showed that the degradation in the accuracy resulting from a shift in the tuning-curve spacing would depend on the plasticity of the higher order decoder of directional information. If there were no plasticity in the interneurons making up the higher order decoder, then the accuracy would be degraded by 50% for a mean tuning-curve shift of only 3.5-degrees. However, if the higher order decoding network were capable of being reoptimized to any arbitrary shift in tuning curves, the degradation in attainable accuracy would be much less severe as shifts of up to 1O-degrees would result in virtually no degradation in the accuracy.5. From these results, two general conclusions can be drawn about the coding of specific stimulus parameters by arrays of sensory cells. First, the effectiveness of the coding of a stimulus parameter by an ensemble of cells with broadly overlapping tuning curves is strictly limited by the intrinsic variance in the cells' responses. Second, the robustness of any sensory system to shifts in tuning-curve characteristics can be greatly enhanced by allowing the higher order "decoder" networks to be capable of reoptimization.