Externalized memory in slime mould and the extended (non-neuronal) mind

The hypothesis of extended cognition (HEC) claims that the cognitive processes that materially realise thinking are sometimes partially constituted by entities that are located external to an agent's body in its local environment. We show how proponents of HEC need not claim that an agent must have a central nervous system, or physically instantiate processes organised in such a way as to play a causal role equivalent to that of the brain if that agent is to be capable of cognition. Focusing on the case of spatial memory, we make our argument by taking a close look at the striking example of Physarum Polycephalum plasmodium (i.e., slime mould) which uses self-produced non-living extracellular slime trails to navigate its environment. We will argue that the use of externalized spatial memory by basal organisms like Physarum is an example of extended cognition. Moreover, it is a possible evolutionary precursor to the use of internal spatial memory and recall in animals thus demonstrating how extended cognition may have emerged early in evolutionary history.