Researchers find unicellular slimy mold with no nervous system that remembers food locations

Having a memory of past events allows us to make smarter decisions for the future. Researchers from the Max Planck Institute for Dynamics and Self-Organization (MPIDS) and the Technical University of Munich (TUM) identify the basis of memory formation in the slime mold Physarum polycephalum, despite its lack of the nervous system.

The ability to store and retrieve information gives an organism a clear advantage when foraging for food or avoiding harmful environments, and has been traditionally linked to organisms with a nervous system. A new study by Mirna Kramar (MPIDS) and Professor Karen Alim (TUM and MPIDS) challenges this view by discovering the surprising abilities of a highly dynamic single-celled organism to store and retrieve information about its environment.

Window on the past

The slimy mold Physarum polycephalum has intrigued researchers for many decades. Existing at the crossroads between the kingdoms of animals, plants and fungi, this unique organism provides insight into the early evolutionary history of eukaryotes. Its body is a giant single cell made up of interconnected tubes that form complex networks. This single amoeba-like cell can span several centimeters, even meters, like the largest cell on earth in the Guinness Book of World Records.

The viscous mold’s striking abilities at solving complex problems such as finding the shortest path through a maze has earned it the attribute “intelligent”, intrigued the research community, and prompted questions about decision-making in the community. most basic levels of life. Physarum’s decision-making ability is particularly fascinating given that its tubular network is constantly undergoing rapid reorganization – growing and disintegrating its tubes – while completely lacking a center of organization. Researchers have found that the body weaves memories of food encounters directly into the body’s networked architecture and uses the stored information when making future decisions.

Decisions are guided by memories

“It’s very exciting when a project develops from simple experimental observation,” says Karen Alim, head of the Biological Physics and Morphogenesis group at MPIDS and TUM Professor on Biological Network Theory, “We have followed the organism’s migration and feeding process and observed a distinct imprint of a food source on the pattern of thicker and thinner tubes in the network long after feeding. Given the highly dynamic reorganization of the P. polycephalum network, the persistence of this imprint sparked the idea that the network architecture itself could serve as a memory of the past. However, we first had to explain the mechanism behind the formation of the imprint. “

To find out what is going on, the researchers combine microscopic observations of the adaptation of the tubular network with theoretical modeling. An 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 network, causing the entire organism to reorient its migration to food. .

“Gradual softening is where existing fingerprints from previous food sources come into play and where information is stored and retrieved,” says Mirna Kramar, the study’s first author. “Past feed events are built into the hierarchy of tube diameters, especially the arrangement of thick and thin tubes in the array. For the softener chemical that is now being transported, the thick network tubes act as highways in the traffic networks, allowing transport throughout the body. Previous encounters imprinted in the architecture of the network influence the decision on the future direction of migration. “

Universal principles inspire design

The authors point out that Physarum’s ability to form memories is intriguing given the simplicity of this living network. “It is remarkable that the body relies on such a simple mechanism and controls it in such a precise way. These results present an important piece of the puzzle for understanding the behavior of this ancient organism and at the same time pointing towards the universal. We envision potential applications of our findings in designing smart materials and building flexible robots that navigate complex environments, ”concludes Karen Alim.