Brainless Slime Mold Excretes Extracellular Slime to Remember Where It Has Been
Posted on October 9, 2012
University of Sydney researchers have found that brainless slime molds can remember using an external spatial memory. They use excreted chemicals as a memory system.
The researchers tested the slime mold's ability to navigate its way out of a U-shaped barrier. As the slime mold (Physarum polycephalum) moves it leaves behind a thick mat of non-living, translucent, extracellular slime. A sugary solution the mold likes to eat was placed on the other side of the U-shaped barrier. The slime mold succeeded in reaching the sugary solution 96% of the time in the allotted 120 hour time limit. Slime mold moves very slowly. The researchers report that it took an average of 57 hours for the mold subjects to solve the U-shaped trap test.
What is most interesting is that the slime mold did not revisit areas it had already slimed. This suggests it can sense extracellular slime upon contact and therefore "remember" and avoid areas it has already explored. However, if the mold is cut off from its slime trail memory it loses this ability.
The researchers compare the slime mold's slimy trail marker to the breadcrumb trail used by Hansel and Gretel in the Grimm fairy tale.
Christopher Reid from the University of Sydney's School of Biological Sciences and leader of the study, said in a statement, "We have shown for the first time that a single-celled organism with no brain uses an external spatial memory to navigate through a complex environment. Results from insect studies, for example ants leaving pheromone trails, have already challenged the assumption that navigation requires learning or a sophisticated spatial awareness. We've now gone one better and shown that even an organism without a nervous system can navigate a complex environment, with the help of externalised memory."
Take a look:
The research was published here in the Proceedings of the National Academy of Sciences journal.