The role of noise in self-organized decision making by the true slime mold Physarum polycephalum

Self-organized mechanisms are frequently encountered in nature and known to achieve flexible, adaptive control and decision-making. Noise plays a crucial role in such systems: It can enable a self-organized system to reliably adapt to short-term changes in the environment while maintaining a generally stable behavior. This is fundamental in biological systems because they must strike a delicate balance between stable and flexible behavior. In the present paper we analyse the role of noise in the decision-making of the true slime mold Physarum polycephalum, an important model species for the investigation of computational abilities in simple organisms. We propose a simple biological experiment to investigate the reaction of P. polycephalum to time-variant risk factors and present a stochastic extension of an established mathematical model for P. polycephalum to analyze this experiment. It predicts that—due to the mechanism of stochastic resonance—noise can enable P. polycephalum to correctly assess time-variant risk factors, while the corresponding noise-free system fails to do so. Beyond the study of P. polycephalum we demonstrate that the influence of noise on self-organized decision-making is not tied to a specific organism. Rather it is a general property of the underlying process dynamics, which appears to be universal across a wide range of systems. Our study thus provides further evidence that stochastic resonance is a fundamental component of the decision-making in self-organized macroscopic and microscopic groups and organisms.

自组织机制在自然界中随处可见，且已被证实能够实现灵活自适应的控制与决策。噪声在这类系统中发挥着关键作用：它可使自组织系统在维持整体稳定行为的同时，可靠地适配环境的短期变化。这一点在生物系统中具有基础性意义，因为生物必须在稳定行为与灵活行为之间达成精妙的平衡。在本研究中，我们分析了噪声在真黏菌多头绒泡菌（Physarum polycephalum）决策过程中的作用，该物种是探究简单生物体计算能力的重要模式物种（model species）。我们设计了一项简单的生物学实验，以探究多头绒泡菌对时变风险因子的响应，并针对多头绒泡菌的现有成熟数学模型构建随机扩展版本，用于分析该实验结果。该模型预测：得益于随机共振（stochastic resonance）机制，噪声可使多头绒泡菌正确评估时变风险因子，而对应的无噪声系统则无法完成这一任务。除针对多头绒泡菌的研究外，我们还证实，噪声对自组织决策的影响并非局限于特定生物体，而是其背后过程动力学的通用属性，这一属性在诸多系统中均普遍存在。因此，本研究进一步佐证了：随机共振是自组织宏观、微观群体及生物体决策过程的核心组成部分。