Remembering past events allows us to make smarter decisions about the future. Researchers at the Max Planck Institute for Dynamics and Self-Organization (MPIDS) and the Technical University of Munich (TUM) have identified the basis for the formation of memories in the mucous mold Physarum polycephalum, despite its lack of a nervous system.

The ability to store and retrieve information gives the body a distinct advantage in finding food or avoiding harmful environmental conditions and has traditionally been associated with organisms that have a nervous system. New research challenges this view, revealing the amazing ability of a highly dynamic, single-celled organism to store and retrieve information about its environment.

The mucous mold Physarum polycephalum has been puzzling researchers for many decades. This unique organism, which exists at the crossroads between the kingdoms of animals, plants and fungi, provides insight into the early evolutionary history of eukaryotes. Its body is a giant single cell made of interconnected tubes that form complex networks. This single amoeba-like cell can stretch to several centimeters or even meters and is the largest cell on Earth in the Guinness Book of Records.

Slime mold’s astounding ability to solve complex problems, such as finding the shortest path through a maze, earned her the title of intelligent unicellular. And it also intrigued the research community and raised questions about decision-making at the most basic levels of life. Physarum’s ability to make decisions is especially impressive given that its tubular network is constantly undergoing rapid reorganization, expanding and breaking down, with the complete absence of the center of decision organization – the nervous system. Researchers have found that the body weaves memories of food encounters directly into the architecture of the network body and uses stored information to make future decisions.

“It is very interesting when a project develops on the basis of simple experimental observation. We observed the process of migration and feeding of the organism and found a distinct imprint of the food source on the structure of the thicker and thinner tubes of the net long after feeding. Given the highly dynamic reorganization of the P. polycephalum network, the persistence of this fingerprint gave rise to the idea that the network architecture itself could serve as a memory of the past. However, first we had to explain the mechanism of forming a fingerprint in memory. “

Karen Alim, Team Leader for Biological Physics and Morphogenesis at MPIDS and Professor of Biological Network Theory at TUM

To figure out what’s going on, the researchers combined microscopic observations of tubular network adaptation with theoretical simulations. The encounter with food triggers the release of a chemical that travels from where the food was found throughout the body and softens the tubes in the body’s network, causing the entire body to reorient its migration toward food.

As a result, past feeding events are embedded in the hierarchy of tube diameters, in particular the arrangement of thick and thin tubes in the network. For the emollient chemical that is currently being transported, the thick tubes in the network act as highways in the transport network, allowing rapid transport throughout the body. Previous meetings, captured in network architecture, influence decisions about the future direction of migration.

The authors emphasize that Physarum’s ability to form memories is intriguing given the simplicity of this living web. It is noteworthy that the body relies on such a simple mechanism and, nevertheless, controls it in such a well-oiled way. These results represent an important piece of the puzzle in understanding the behavior of this ancient organism and at the same time point to the universal principles underlying behavior.

Such a discovery could give impetus to the application of the results in the development of intelligent materials and the creation of soft robots that move in complex environments.