It has been demonstrated experimentally that slow and fast conduction waves with distinct conduction velocities can occur in the same nerve system depending on the strength or the form of the stimulus, which give rise to two modes of nerve functions. However, the mechanisms remain to be elucidated. In this study, we use computer simulations of the cable equation with modified Hodgkin-Huxley kinetics and analytical solutions of a simplified model to show that stimulus-dependent slow and fast waves recapitulating the experimental observations can occur in the cable, which are the two stable conduction states of a bistable conduction behavior. The bistable conduction is caused by a positive feedback loop of the wavefront upstroke speed, mediated by the sodium channel inactivation properties. Although the occurrence of bistable conduction only requires the presence of the sodium current, adding a calcium current to the model further promotes bistable conduction by potentiating the slow wave. We also show that the bistable conduction is robust, occurring for sodium and calcium activation thresholds well within the experimentally determined ones of the known sodium and calcium channel families. Since bistable conduction can occur in the cable equation of Hodgkin-Huxley kinetics with a single inward current, i.e., the sodium current, it can be a generic mechanism applicable to stimulus-dependent fast and slow conduction not only in the nerve systems but also in other electrically excitable systems, such as cardiac muscles.

实验证明，根据刺激的强度或形式，同一神经系统中可以出现具有不同传导速度的慢传导波和快传导波，从而产生两种神经功能模式。然而，其机制仍有待阐明。在这项研究中，我们使用修正的霍奇金-赫胥黎动力学和简化模型的解析解对电缆方程进行计算机模拟，以表明电缆中可以出现重现实验观察结果的刺激依赖性慢波和快波，这是两种稳定的波双稳态传导行为的传导状态。双稳态传导是由波前上行速度的正反馈回路引起的，由钠通道失活特性介导。虽然双稳态传导的发生只需要钠电流的存在，但在模型中添加钙电流可以通过增强慢波进一步促进双稳态传导。我们还表明，双稳态传导是稳健的，发生的钠和钙激活阈值完全在已知钠和钙通道家族的实验确定的阈值内。由于双稳态传导可以在具有单个内向电流（即钠电流）的霍奇金-赫胥黎动力学的电缆方程中发生，因此它可以是一种通用机制，适用于刺激依赖性的快速和慢速传导，不仅适用于神经系统，而且适用于神经系统。其他可电兴奋的系统，例如心肌。