A neon yellow slime mold can store memories, although it has no nervous system. Now, scientists have found a new clue as to how the brainless bubble achieves this impressive feat.
The single-celled organism, known as Physarum polycephalum, belongs to the taxonomic group Amoebozoa, the same group that amoebas, Live Science previously reported. The bubbles can exist as a tiny cell with a nucleus, the cell’s control center, or several cells can fuse to form a giant cell with many nuclei. These fused cells can grow to cover tens of square inches (hundreds of square centimeters) in area.
When fused, the huge cells form a complex network of internal tubes; these tubes contract, similar to blood veins, to push fluids and nutrients through the brainless bubble.
The new study, published on February 22 in the journal Proceedings of the National Academy of Sciences, shows that the diameters of these branched tubes can encode information, such as where the slime mold found food recently. When the bubble finds food, it quickly reorganizes its tubular network, widening some tubes and shrinking others, and this architecture remains in place even after the bubbles have eaten the food.
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This basic form of memory can help viscous fungi solve complex puzzles, such as finding the fastest route to food or the shortest path through a maze, senior author Karen Alim, an associate professor of biological physics at the Technical University of Munich, told Live Science by email.
When P. polycephalum detects a nearby snack, by detecting chemicals that your food releases, the tubes closest to the food begin to expand. Meanwhile, the tubes further away from the food shrink and sometimes disappear entirely, being reabsorbed by the sludge. The slime mold then creeps towards the large, dilated tubes, migrating until it swallows your snack.
But even after swallowing each piece of food, the slime mold clings to the cluster of thick tubes, leaving a lasting “impression” of where the food was located, the authors wrote. This dictates how the fluid flows through the entire network and influences the direction the slime mold travels next. For example, if more food appears near the thick printed tubes, the slime mold is already prepared to spread in that direction, and this printed “memory” becomes reinforced.
“At the brain, we store information by strengthening or weakening the connections between individual neurons, “a type of nerve cell that sends electrical and chemical signals, Alim said.” Each additional impulse can strengthen a strong existing connection “.
A similar – but simplified – process shapes memory formation within viscous fungi, she said.
And, like connections in the brain, “memories” of slime mold can become weaker if not reinforced, Alim added. While the tubes next to the food get thicker, the tubes away from the food get thinner and can disappear. “Memories disappear when the tubes retract. And disappear” in the larger slime mold, Alim said. In this way, old memories of food can be replaced as the bubble migrates and hunts for new nutrients.
Previous studies of viscous fungi also suggested that the “slime fungus network adapts to external signals and that the network could be used as a reading of what the viscous fungus experienced,” said Audrey Dussutour, a researcher who studies cognitive processing in ants and viscous fungi at the University of Toulouse, France. The new study provides more evidence of how and why the tubular network reorganizes, Dussutour, who was not involved in the research, told Live Science via email.
“The results remind me of networks of trails on ants,” where forage ants leave a trail of chemicals for other ants to follow, added Dussutour. As more ants follow the same trail and deposit more chemicals, more ants tend to follow the well-used rather than another, less traveled trail, according to a 2005 report that Dussutour co-authored the newspaper. Proceedings of the Royal Society B.
However, although scientists know which pheromones the ants secrete to leave their tracks, it is uncertain which signal tells the tubes to widen and others to shrink, Alim said.
Based on laboratory experiments and computer models of P. polycephalum, the authors suspect that the slime mold produces some soluble substance when feeling the food and that this substance causes the tubes closest to the food to soften and stretch. As the gelatinous walls of the tubes extend, part of the substance leaks into the larger network of tubes and becomes more diluted as it progresses. Therefore, tubes far from the food source receive very little of the substance, if any, explained the study’s authors.
Although there is evidence that this mysterious chemical drives the expansion of the tube, unfortunately we have no idea of its chemical composition, “said Alim. This will be the focus of future research.
In addition, “the next step is to ask how many memories can be stored on a network and whether we can transfer the mechanism to synthetic systems to build intelligent materials,” said Alim. These smart materials would mimic the live flow networks found in viscous fungi and could be used to build soft-bodied robots, for example, according to a statement.
Originally published on Live Science.