The mucus form Physarum polycephalum consists of a single biological cell. With micro-injection you can mark the flow in Physarum in color. Credit: Bjoern Kscheschinski / MPIDS
How a unicellular mucus form makes smart decisions without a central nervous system.
With the memory of events in the past, we can make smarter decisions about the future. Researchers from the Max Planck Institute for Dynamics and Self-Organization (MPI-DS) and the Technical University of Munich (TUM) have now identified how the slime form Physarum polycephalum saves memories – although it has no nervous system.
The ability to store and retrieve information gives an organism a clear advantage when searching for food or avoiding harmful environments. Traditionally, it is attributed to organisms that have a nervous system.
A new study, written by Mirna Kramar (MPI-DS) and prof. Karen Alim (TUM and MPI-DS), challenge this view by discovering the surprising abilities of a highly dynamic, unicellular organism to store and retrieve information about its environment.
Window to the past
The slime form Physarum polycephalum has been surprising 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 – to which humans also belong.
Prof. Karen Alim, Technical University of Munich, and Mirna Kramar, Max-Planck Institute for Dynamics and Self-Organization, discovered how the slime form Physarum polycephalum weaves its memories of food encounters directly into the architecture of the network-like body and uses the stored information when making future decisions taken. Credit: Bilderfest / TUM
Its body is a giant single cell made up of interconnections that form complex networks. This single amoeba-like cell can stretch a few centimeters or even meters, and is the largest cell on earth in the Guinness Book of World Records.
The network architecture as a memory
“It is very exciting when a project develops from a simple experimental observation,” says Karen Alim, head of the group biological physics and morphogenesis at the MPI-DS in Göttingen and professor of biological network theory at the Technical University of Munich.
When the researchers followed the migration and feeding process of the organism and saw a clear imprint of a food source on the pattern of thicker and thinner tubes of the network, long after feeding.
The mucus form Physarum polycephalum consists of a single biological cell. Because of his ingenious ability to adapt his pipe network to a changing environment, he is called ‘intelligent’. Researchers from TUM and MPI-DS have now discovered how it stores information – even without having a nervous system or brain. Credit: Nico Schramma / MPI-DS
“Given the extremely dynamic network reorganization of P. polycephalum, the persistence of this print has fueled the idea that network architecture itself can serve as a memory of the past,” says Karen Alim. However, they first had to explain the mechanism behind the formation of the print.
Decisions are guided by memories
For this purpose, the researchers combined microscopic observations of the adaptation of the pipe network with theoretical modeling. An encounter with food causes the release of a chemical that moves from the place where food is found by the whole organism, and softens the tubes in the network, which shifts the whole organism in the direction of the food.
“The gradual softening is where the existing prints of previous food sources come into play and where information is stored and retrieved,” says first author Mirna Kramar. “Past feeding events are embedded in the hierarchy of tube diameters, specifically in the arrangement of thick and thin tubes in the network.”
“For the emollient chemical now being transported, the thick tubes in the network serve as highways in traffic networks, enabling rapid transport throughout the organism,” adds Mirna Kramar. “Previous encounters that have been imprinted in the network architecture therefore weigh in the decision on the future direction of migration.”
Design based on universal principles
“Given the simplicity of this live network, the ability of Physarum to form memories is intriguing. It is remarkable that the organism relies on such a simple mechanism and yet controls it in such a fine way, ”says Karen Alim.
‘These results are an important piece of the puzzle to understand the behavior of this ancient organism and at the same time indicate universal principles underlying behavior. We envisage potential applications of our findings in the design of smart materials and the construction of soft robots that navigate through complex environments, ”concludes Karen Alim.
Reference: “Encoding memory in tube diameter hierarchy of living flow network” by Mirna Kramar and Karen Alim, 23 February 2021, Proceedings of the National Academy of Sciences.
DOI: 10.1073 / pnas.2007815118