Decision making behaviors in a brainless organism (<i>Physarum polycephalum</i>) can emerge from self-organized physical interactions within a single cell.

Decision-making is traditionally studied in the context of neurobiology. However, little is known about complex decision-making abilities that arise even in the absence of neurons. In this study, we use a brainless unicellular protist Physarum polycephalum (slime mold) to examine the mechanisms it employs to “choose” one food source over another. Previous studies show that an underlying network of actin fibers drives membrane contractions, leading to pressure gradients, fluid flow and ultimately locomotion. Our observations suggest that the local disintegration of the actin network may cause the slime mold to bias its movement towards one food source. We use a dynamical systems approach to model pressure interactions, volume exchange and actin disintegration to explore the emergence of a system-wide decision. Through this model, we demonstrate that stable contraction patterns similar to empirical observations can emerge through purely physical interactions. Furthermore, the “choice” of one food source over another can also be explained by locally reducing the contractile response of the actin network. These results indicate that complex decision-making behaviors can arise from purely physical interactions within a single cell, bypassing the need for a nervous system.