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This Is How Slime Mold Makes Memories, Despite Having No Brain

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Tom Hale

Senior Journalist

clockMar 2 2021, 11:19 UTC
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Slime mold.

The slime mold Physarum polycephalum consists of a single biological cell.  Image credit:Bjoern Kscheschinski / MPIDS

It may just look like a yellowish streak of gunk, but slime molds are a strong contender for the world’s most bizarre lifeform. As shown by a new study, it appears this spindly clump of life is able to "remember" information and act on their "memories:" a pretty impressive feat considering they lack any form of central nervous system.

The species studied here is Physarum polycephalum, which means many-headed slime. Despite their name, slime molds are not mold nor fungi, but eukaryotes, the same domain as humans and other animals. They are not your average single-celled organism, however. Instead, they consist of a collection of individual cells that have become bound together in an unusual unified form, complete with multiple nuclei encased in a single giant cell. Extending out of this giant single cell, the slime mold has a network of tiny intertwined tubes.

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The organisms can be chopped up into many pieces, but will eventually fuse back together. If one slime mold comes across another along their travels, they are also capable of joining together to form an even larger organism. They might sound like aliens, but they can be found in many humid and dark environments, such as leaf litter and among the rotting debris of forests.

Just as previous experiments have shown, slime molds can even display what might be considered a form of "intelligence." If confronted with a maze towards a food source, they can “work out” the shortest and easiest path. If presented with a variety of food sources, it identifies the most rewarding and prioritizes it. In a new study, scientists have now demonstrated that slime molds appear to possess something that resembles memory. While on the hunt, they are able to remember the location of the food and then retrieve information about the environment to return for another time. 
slime moldy.
Another image of the P. polycephalum from the study. Image credit:Bjoern Kscheschinski / MPIDS

As reported in the journal, Proceedings of the National Academy of Sciences, scientists at the Max Planck Institute for Dynamics and Self-Organization and the Technical University of Munich in Germany demonstrated this by closely watching a P. polycephalum while encountering food. Their observations showed that the slime mold released a trail of chemicals after leaving a location with food. This chemical softens the tubes in the network of the slime mold, causing them to grow in diameter while other tubes shrink. Using theoretical modeling, the researchers found that this softening of the tubes reorganizes the network and reorients the organism towards the direction of where food was once found. 

In other words, the location of the food is imprinted within the network's architecture, which acts as a means to store and recover the information.

The gradual softening is where the existing imprints of previous food sources come into play and where information is stored and retrieved", Mirna Kramar, first author of the study from the Max Planck Institute, said in a statement. "Past feeding events are embedded in the hierarchy of tube diameters, specifically in the arrangement of thick and thin tubes in the network."

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"For the softening chemical that is now transported, the thick tubes in the network act as highways in traffic networks, enabling quick transport across the whole organism," adds Kramar. "Previous encounters imprinted in the network architecture thus weigh into the decision about the future direction of migration."


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