The Origins of Memory

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The slime mould Physarum polycephalum is a single-celled organism without an obvious nervous system. Nevertheless, it has recently been shown to use an external spatial memory to navigate. When it explores an environment, it leaves behind a trail of extracellular slime, which if it encounters later, it strongly avoids. This response ensures that the organism does not revisit areas that it has already investigated.  The avoidance behaviour is also a choice because when no previously unexplored territory is available, the slime mould no longer avoids the slime. In essence then it possesses an externalised memory, which because it relies on feedback from chemicals, maybe a precursor to our own. Here the tracks left behind by the slime mould, or that is its memory, have been revealed using a DIC microscope. The spaces occupied by its filaments can be clearly seen surrounded by small crystals which must represent its memory

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