Brainless but Multi-Headed: Decision Making by the Acellular Slime Mould Physarum polycephalum.

Because of its peculiar biology and the ease with which it can be cultured, the acellular slime mould Physarum polycephalum has long been a model organism in a range of disciplines. Due to its macroscopic, syncytial nature, it is no surprise that it has been a favourite amongst cell biologists. Its inclusion in the experimental tool kit of behavioural ecologists is much more recent. These recent studies have certainly paid off. They have shown that, for an organism that lacks a brain or central nervous system, P. polycephalum shows rather complex behaviour. For example, it is capable of finding the shortest path through a maze, it can construct networks as efficient as those designed by humans, it can solve computationally difficult puzzles, it makes multi-objective foraging decisions, it balances its nutrient intake and it even behaves irrationally. Are the slime mould's achievements simply "cute", worthy of mentioning in passing but nothing to take too seriously? Or do they hint at the fundamental processes underlying all decision making? We will address this question after reviewing the decision-making abilities of the slime mould.