The slime mold Physarum polycephalum remembers where it’s been, allowing the single-cell amoeboid to more efficiently navigate its environment. The key, according to a study published yesterday (October 8) in Proceedings of the National Academy of Sciences, a kind of externalized spatial memory system, based on the trail of translucent slime it leaves in its wake, that allows the organism to recognize and avoid already-explored areas.

“It doesn’t have a brain. It doesn’t even have a neuron. It has to do everything with just one cell,” Audrey Dussutour, a collective behavior specialist at France’s National Center for Scientific Research, told Wired Science. “The easiest way to have a memory of where you’ve been is to leave something behind.”

When Dussutour and her colleagues noticed that foraging P. polycephalum do not often cross earlier paths, they decided to put the slime mold to the test. The researchers presented P. polycephalum with an agarose-floored Y-maze with food at the end of both arms, but in one of the arms, they covered the agar with extracellular slime; 39 of 40 went down the arm with blank agar, avoiding the slime. When both arms contained slime or both arms lacked slime, P. polycephalum showed no preference.