A mathematical model of the retina based on neurophysiological mechanisms

脊椎动物视网膜一直被认为是大脑的窗口，因为它的可及性和适合神经科学研究。它被认为是脊椎动物大脑中为数不多的可以合理解释其用途和工作原理的部分之一。视网膜是信息处理神经网络的理想模型，描述了神经元如何相互作用来编码和处理视觉信息。在过去的十年里，我们基于生物物理细节开发了视网膜神经元的数学模型。这些模型可以揭示如果一个特定的离子电流是活跃的或不活跃的会发生什么。然后我们可以问，在神经元中存在特定种类的离子通道对视觉系统有什么好处。在这项研究中，我们分析了杆状光感受器作为带通滤波器的潜在机制。模拟的频率响应表明，单棒具有带通滤波器的特性，其特性受刺激强度和频率的影响。我们分析了单个离子电流对带通滤波的贡献，发现小信号的滤波主要由钙依赖电流调节，而大信号的滤波则由超极化激活电流调节。主要的发现是离子电流的动力学，IK(Ca), ICl（Ca）和Ih表征了棒信号的带通滤波。我们还开发了视网膜神经节细胞产生脉冲的随机模型。该随机模型成功地再现了精确可靠的波动电流注入尖峰。结果表明，脉冲时间的变化主要受向外K电流、IKv和IA的影响。

The vertebrate retina has been thought to be a window to the brain because of its accessibility and suitability for neuroscientific investigation. It is thought to be one of the few parts of the vertebrate brain where we can reasonably explain its purpose and how it works. The retina is an ideal model of an information processing neural network, describing how neurons interact to codify and process visual information. Over the last decade, we have developed mathematical models of retinal neurons based on biophysical details. These models can reveal what happens if a particular ionic current is active or inactive. One can then ask what advantages are given on the visual system by having the particular class of ion channel present in the neuron.In this study, we analyzed the underlying mechanisms of a rod photoreceptor that behaves as a bandpass filter. The simulated frequency response revealed that a single rod behaves as a bandpass filter whose characteristics are affected by the stimulus strength and frequency. We analyzed the contribution of individual ionic currents to bandpass filtering and found that the filtering of small signals is largely regulated by the calcium-dependent currents, whereas the filtering of large signals is regulated by the hyperpolarization-activated current. The major discovery was that the kinetics of the ionic currents, IK(Ca), ICl(Ca), and Ih characterize the bandpass filtering of rod signals. We also developed a stochastic model of spike generation in retinal ganglion cells. The stochastic model succeeded to reproduce precise and reliable spikes to flucutuating current injection. We found the spike timing variability was much influenced by the outward K currents, IKv and IA.