Physarum polycephalum: Establishing an Assay for Testing Decision-making Under Shifting Somatic Boundaries

Prior studies of decision-making generally assume a fixed agent which maximizes utility among its various options. Physarum polycephalum is a popular model for basal cognition that can be cut into pieces that may or may not re-join. We exploited this capacity to develop a novel assay in which radical changes to the agent itself are among the options of the decision-making process. Specifically, we transected a Physarum culture in the presence of a food reward that was located closer to the new smaller piece. In this scenario, the newly created branch must choose between exploiting the reward itself, or first re-connecting with the original mass (and sharing the nutrient reward across a large body). We report a pilot study establishing a protocol in which the number of agents is part of the decision-making process. We observed that despite the presence of food, new branches strongly prefer to merge back to the syncytium before exploiting the reward. Many improvements to the protocol are possible, to extend this effort to understand the interplay between behavioral options and the structure and boundary of the individual making choices in its environment.