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Brainless Slime Mold Found To Be Capable Of Learning

An international team of scientists announced this week that they have discovered learning behaviors in colonies of single-celled organisms. The study, published in The Proceedings of Royal Society B, outlines how the slime mold Physarum polycephalum has been observed to change behaviors in response to stimuli and repeat those behaviors later.

Physarum polycephalum

Physarum polycephalum

For this experiment, researchers placed a small number of Physarum polycephalum cells in a petri dish across from a food source for the slime to move towards. Next, the researchers placed a small amount of a bitter substance such as quinine or caffeine across the middle of the dish. The slime reacted by moving around the bittering agent through a narrow path the researchers left for it. The next time food was placed opposite the slime, the organism took the same route through the narrow path it previously took to avoid the bittering agent.

The same slime mold has been observed in previous studies to solve simple computational problems or even find solutions to classic “minimal length” problems in mazes. A 2008 Japanese study even found that Physarum polycephalum has a very primitive form of memory, and can anticipate future stimuli. One of the researchers in that study, Toshiyuki Nakagaki, argues that the many-headed slime challenges many of our notions about single-celled organisms:

The organism is able to remember periodic changes that it has not experienced before. This indicates that the organism has a generalized capacity for learning

Physarum polycephalum is typically found growing on decaying leaves or tree trunks and has a yellowish, slimy appearance. Its name in Latin literally means “many-headed slime,” and the name might give some clues as to how the organism displays learning-like behaviors. While it is theorized that the individual cells within this slime mold might be able to share information about stimuli, the specific mechanism that enables these behaviors is still unknown.

Physarum polycephalum

Physarum polycephalum “navigating” a maze

The study of this slime mold sheds light on how information sharing works at the cellular level and could potentially lead to discoveries about how learning evolved into the forms of intelligence seen in higher order organisms. So, outdoorsmen and women, the next time you see slime growing up the side of a tree, remember to be courteous – it could be learning from you.