How a viscous single cell mold makes smart decisions

How a single cell slime mold makes smart decisions without a central nervous system.

Having a memory of past events allows us to make smarter decisions for the future. Researchers at the Max-Planck Institute for Dynamics and Self-Organization (MPI-DS) and Technical University of Munich (TUM) have now identified how the slime mold Physarum polycephalum saves memories – although it does does not have a nervous system.

The ability to store and retrieve information gives an organism a clear advantage when foraging for food or avoiding harmful environments. Traditionally, it has been attributed to organisms with a nervous system.

New study by Mirna Kramar (MPI-DS) and Professor Karen Alim (TUM and MPI-DS) challenges this view by uncovering the surprising abilities of a highly dynamic single-celled organism to store and retrieve information on 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 – to which humans also belong.

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, and is the largest cell in the world in the Guinness Book of Records.

Network architecture as memory

“It’s very exciting when a project develops from a simple experimental observation,” says Karen Alim, head of the Biological Physics and Morphogenesis group at MPI-DS in Göttingen and professor of biological network theory at the University. Munich technique.

When the researchers 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.

“Considering the very dynamic reorganization of the P. polycephalum network, the persistence of this imprint gave rise to the idea that the network architecture itself could serve as a memory of the past,” explains Karen Alim. However, they first had to explain the mechanism behind the formation of the imprint.

Decisions are guided by memories

To do this, the researchers combined 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 first author Mirna Kramar. “Past feed events are built into the hierarchy of tube diameters, particularly in the arrangement of thick and thin tubes in the array.”

“For the softening chemical that is now being transported, the thick network tubes act as highways in the traffic networks, allowing rapid transport throughout the body,” adds Mirna Kramar. “The previous encounters imprinted in the architecture of the network thus influence the decision on the future direction of migration.”

Design based on universal principles

“Given the simplicity of this living network, Physarum’s ability to form memories is intriguing. It is remarkable that the organism relies on such a simple mechanism while controlling it in such a fine way, ”says Karen Alim.

“These findings present an important piece of the puzzle in understanding the behavior of this ancient organism and at the same time point to some universal principles underlying the behavior. We envision potential applications of our findings in designing smart materials and building flexible robots that navigate complex environments, ”concludes Karen Alim.

Reference: “Memory encoding in the hierarchy of tube diameters of the living network” by Mirna Kramar and Karen Alim, February 23, 2021, Proceedings of the National Academy of Sciences.
DOI: 10.1073 / pnas.2007815118