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It may be a single-celled organism, but slimy mold Physarum polycephalum has some pretty fascinating stuff in her pretty yellow sleeves. Now, new research has revealed that he seems to “remember” where he previously found food sources – even without a brain or nervous system.
This could help explain how networked organisms can not only live, but thrive, in complex environments, the researchers said – and could also be a key to understanding the mechanisms of memory formation in these species.
P. polycephalum is one of the most unique forms of life on Earth. It is neither a plant, nor an animal, nor a fungus, but a species of unicellular complex amoeba of the protist kingdom (sort of catch-all group for everything that cannot be categorized properly in the other three kingdoms) .
At the start of its life cycle, P. polycephalum exists as a single cell with a single nucleus, but later it fuses with other cells to form a huge single cell with millions of nuclei inside.
This is the plasmodium stage, and the organism can grow to cover an area of up to several square meters. Its body is made up of a complex network of interconnected tubes, the compression of which creates a flow between different regions. This network can quickly develop and reorganize itself to maximize its use of its environment.
A Physarum plasmodium. (Carolina Biological Supply Company / Flickr / CC BY-NC-ND 2.0)
In 2000, Japanese researcher Toshiyuki Nakagaki from RIKEN discovered that P. polycephalum was able to solve a simple maze to reach a food source. Since then, scientists have discovered several intelligent-type behaviors, such as being able to effectively solve the traveling salesman’s problem and “remember” substances.
In her latest tip, biological physicists Mirna Kramar and Karen Alim from the Max Planck Institute for Dynamics and Self-organization in Germany discovered, P. polycephalum uses the very architecture of his body to store memories of where he previously found food.
“We 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,” explained Alim. .
“Given P. polycephalumThe very dynamic reorganization of the network, the persistence of this imprint, gave rise to the idea that the architecture of the network itself could serve as a memory of the past. However, we had to first explain the mechanism behind the formation of the imprint. “
Using microscopic observations, they carefully studied how the body organized itself around a food source. They then used theoretical modeling to understand what was going on inside the viscous mold during this process.
They concluded that the discovery of a food source triggers the release of a chemical that locally softens the tube wall at the food site. This then triggers the expansion of the tubes, becoming wider, to accelerate the flow within the viscous mold to the site.
The chemical also signals the entire body where food is, so it can move to the site and focus on eating.
P. polycephalum may reabsorb parts of its body if it extends exploration tubes in an inhospitable area or contains nothing of interest. But when he has found and eaten a nutritious meal, those thick tubes stay in place so he can quickly return to the site if the food should reappear, the researchers found.
“Gradual softening is where existing fingerprints from previous food sources come into play and where information is stored and retrieved,” Kramar said.
“Past feed events are built into the hierarchy of tube diameters, especially the arrangement of thick and thin tubes in the array. For the softening chemical that is now 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. “
It’s not quite different from how the human brain works. One needs to be careful drawing parallels between slime mold and the human brain, but there are some interesting similarities that might help us understand how information coding works in various types of organisms.
In this case, the synapses, which send information between neurons, get stronger as we learn and get stronger as we use them, but can weaken if we don’t – vaguely similar to the tubes of the slimy mold. , which will become thicker at the sites of interest, but will die or be reabsorbed if their presence is no longer useful to the body.
“It is remarkable that the body relies on such a simple mechanism while controlling it in such a fine way,” Alim said.
“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. “
The research was published in PNAS.
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