Institute for Neurobiology, Eberhardt Karls Universität Tübingen, Tübingen, Germany.
Systems Neurobiology, Werner Reichard Center for Integrative Neurobiology, Universität Tübingen, Tübingen, Germany.
PLoS Comput Biol. 2023 Aug 11;19(8):e1010871. doi: 10.1371/journal.pcbi.1010871. eCollection 2023 Aug.
Studies on population coding implicitly assume that spikes from the presynaptic cells arrive simultaneously at the integrating neuron. In natural neuronal populations, this is usually not the case-neuronal signaling takes time and populations cover a certain space. The spread of spike arrival times depends on population size, cell density and axonal conduction velocity. Here we analyze the consequences of population size and axonal conduction delays on the stimulus encoding performance in the electrosensory system of the electric fish Apteronotus leptorhynchus. We experimentally locate p-type electroreceptor afferents along the rostro-caudal body axis and relate locations to neurophysiological response properties. In an information-theoretical approach we analyze the coding performance in homogeneous and heterogeneous populations. As expected, the amount of information increases with population size and, on average, heterogeneous populations encode better than the average same-size homogeneous population, if conduction delays are compensated for. The spread of neuronal conduction delays within a receptive field strongly degrades encoding of high-frequency stimulus components. Receptive field sizes typically found in the electrosensory lateral line lobe of A. leptorhynchus appear to be a good compromise between the spread of conduction delays and encoding performance. The limitations imposed by finite axonal conduction velocity are relevant for any converging network as is shown by model populations of LIF neurons. The bandwidth of natural stimuli and the maximum meaningful population sizes are constrained by conduction delays and may thus impact the optimal design of nervous systems.
研究人员对群体编码进行了深入研究，认为来自突触前细胞的尖峰信号会同时到达整合神经元。然而，在自然神经元群体中，这种情况通常不会发生，因为神经元信号的传递需要时间，而且群体覆盖了一定的空间。尖峰到达时间的传播取决于群体大小、细胞密度和轴突传导速度。在本文中，我们分析了电鱼 Apteronotus leptorhynchus 的电感觉系统中群体大小和轴突传导延迟对刺激编码性能的影响。我们通过实验沿着身体的前后轴定位了 p 型电感受器传入神经，并将其位置与神经生理响应特性联系起来。在信息理论的方法中，我们分析了同质和异质群体的编码性能。正如预期的那样，信息的数量随着群体大小的增加而增加，并且如果补偿了传导延迟，异质群体的平均编码效果通常优于同尺寸的同质群体。在一个感受野内神经元传导延迟的扩散强烈降低了高频刺激成分的编码。在 Apteronotus leptorhynchus 的电感觉侧线叶中发现的感受野大小似乎是在传导延迟和编码性能之间的良好折衷。有限的轴突传导速度所带来的限制对于任何汇聚网络都是相关的，这可以通过 LIF 神经元的模型群体来证明。自然刺激的带宽和最大有意义的群体大小受到传导延迟的限制，因此可能会影响神经系统的最佳设计。
