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How unicellular mold molds make smart decisions

Physarum polycephalum

The mucus mold Physarum polycephalum consists of a biological cell. Microinjection allows the color flow in Physarum to be noted. Credit: Bjoern Kscheschinski / MPIDS

How unicellular mucus mold makes intelligent decisions without a central nervous system.

Having a memory of past events allows us to make smarter decisions about the future. Researchers at the Max-Planck Institute for Dynamics and Self-Organization (MPI-DS) and the Technical University of Munich (TUM) have already found that the slime mold Physarum polycephalum saves memories – even though there is no nervous system.

The ability to store and recover information gives the body a clear advantage in finding food or avoiding harmful environments. It is traditionally attributed to organisms that have a nervous system.

A new study by Mirna Kramar (MPI-DS) and Prof. Karen Alim (TUM and MPI-DS) challenges this view, revealing the surprising ability of a highly dynamic, single-celled organism to store and retrieve information about its environment.

A window to the past

The Physarum polycephalum has puzzled researchers for many decades. Existing at the crossroads between the kingdoms of animals, plants and fungi, this unique organism gives an idea of ​​the early evolutionary history of eukaryotes – to which humans also belong.

Karen Alim

Prof. Karen Alim, Technical University of Munich, and Mirna Kramar, Max Planck Institute for Dynamics and Self-Organization, discovered how the slime mold Physarum polycephalum intertwines its memories of encounters with food directly in the architecture of the network-like body and uses stored information to make future solutions. Credit: Bilderfest / TUM

Its body is a giant single cell made up of interconnected tubes that form complex networks. This single amoeba-like cell can extend several centimeters or even meters, posing as the largest cell on earth in the Guinness Book.

Network architecture as memory

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

When researchers traced the process of migration and nutrition of the body and noticed a clear imprint of a food source on the model of thicker and thinner tubes on the network long after eating.

Physarum polycephalum in Petri Dish

Physarum polycephalum consists of a single biological cell. Due to its ingenious ability to adapt its pipe network to the changing environment, it is called “intelligent”. Now researchers at TUM and MPI-DS have figured out how it stores information – even without a nervous system or brain. Credit: Nico Schrama / MPI-DS

“Given the highly dynamic reorganization of the P. polycephalum network, the persistence of this footprint gave rise to the idea that the network architecture itself could serve as a memory of the past,” says Karen Alim. First, however, they had to explain the mechanism behind the imprint.

Decisions are guided by memories

To this end, the researchers combined microscopic observations of pipe network adaptation with theoretical modeling. Encountering food causes the release of a chemical that travels from where food is found throughout the body and softens the tubes in the network, causing the whole body to reorient its migration to food.

“Gradual softening is where fingerprints from previous food sources exist and where information is stored and retrieved,” says first author Mirna Kramar. “Past feeding events are embedded in the hierarchy of tube diameters, in particular the arrangement of thick and thin tubes in the net.”

“For the emollient chemical that is now being transported, the thick pipes in the network act as highways in the traffic networks, which allows fast transport throughout the body,” adds Mirna Kramar. “Previous meetings, sealed in the network architecture, thus weigh on 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’s remarkable that the body relies on such a simple mechanism and yet controls it in such a subtle way, “says Karen Alim.

“These results are an important part of the puzzle in understanding the behavior of this ancient organism and at the same time point to the universal principles underlying the behavior. We anticipate potential applications of our discoveries in the design of intelligent materials and the construction of soft robots that move through complex environments, ”concludes Karen Alim.

Reference: “Memory coding in the hierarchy of the diameter of the pipe of the network of living streams” by Mirna Kramar and Karen Alim, February 23, 2021, Notices of the National Academy of Sciences.
DOI: 10.1073 / pnas.2007815118

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