This freakishly smart, crawling slime is redefining how we understand intelligence : ScienceAlert
Imagine that you are walking through the forest, and your foot trips over a log. On its underside, something wet and yellow is spreading – a bit like something you might have sneezed on… if it’s something banana-yellow and spreading out into elegant fractal branches.
What you would see is a plasmodium shape Physarum polycephalum, many-headed slime mold. Like other slime molds found in nature, it fulfills an important ecological role, helping to break down organic matter so that it can be recycled into the food web.
This bizarre little organism has no brain, no nervous system; its mottled, bright yellow body is just one cell. This type of slime mold thrives, more or less unchanged, for a billion years in its moist, decaying habitats.
And, in the last decade, it has changed the way we think about cognition and problem solving.
“I think it’s the same kind of revolution that happened when people realized that plants can communicate with each other,” said biologist Audrey Dussutour of France’s National Center for Scientific Research.
“Even these tiny little microbes can learn. It gives you a little humility.”
P. polycephalum – which Dussutour has given the adorable nickname “The Blob” – is not exactly a rarity. It can be found in dark, moist, cool environments such as leaf litter on the forest floor. It’s also really unusual; although we call it ‘mold’, it is not actually a fungus. It’s neither an animal nor a plant, but a member of the protist kingdom—a kind of catch-all group for anything that can’t be neatly categorized into the other three kingdoms.
It begins life as multiple single cells, each with a single nucleus. Then they merge and form plasmodiumthe vegetative life stage in which the organism feeds and grows.
In this form, spreading through the veins in search of food and exploring the environment, it is still a single cell, but it contains millions or even billions of nuclei swimming in a cytoplasmic fluid enclosed within a light-yellow membrane.
Cognition without the brain
Like all organisms, P. polycephalum he must be able to make decisions about his environment. You need to look for food and avoid danger. It must find ideal conditions for its reproductive cycle. And this is where our little yellow friend gets really interesting. P. polycephalum it has no central nervous system. It doesn’t even have specialized tissues.
“We’re talking about cognition without a brain, obviously, but also without any neurons. So the underlying mechanisms, the whole architectural framework of how it deals with information is completely different to the way your brain works,” biologist Chris Reid of Macquarie University in Australia told ScienceAlert 2021.
“By giving it the same problem-solving challenges that we’ve traditionally given to animals with brains, we can begin to see how this fundamentally different system might achieve the same outcome. It then becomes clear that for many of these things—that we’ve always thought required a brain or some kind of higher information processing system—that’s not always necessary.”
P. polycephalum is well known to science. Decades ago, it was, as physicist Hans-Günther Döbereiner of the University of Bremen in Germany explained, “the workhorse of cell biology.” It was easy to clone, store and study.
However, as our tools for genetic analysis have developed, organisms such as mice or cell lines such as HeLa assumed, i P. polycephalum fell by the wayside.
In 2000, biologist Toshiyuki Nakagaki of RIKEN in Japan brought the little beast out of retirement—and not because of cell biology. His paper, published in Natureit was titled “Maze Solving by an Amoeboid Organism” – and that’s exactly what P. polycephalum done.
Nakagaki and his team placed a piece of plasmodium at one end of a maze, a food reward (oats, because P. polycephalum loves oat bacteria) on the other, and watched what happened.
The results were astounding. This strange little cellless organism managed to find the fastest way through every maze thrown at it.
“That set off a wave of research into what other kinds of more severe scenarios we can test for slime mold,” Reid said.
“Almost all of them were surprising in one way or another, and surprised the researchers with how the slime mold actually behaved. It also revealed some limitations. But mostly, it was a journey of discovery about how this simple creature can perform tasks that have always been given and considered the domain of higher organisms.”
Full of surprises
Nakagaki recreated the Tokyo subway, with station nodes marked with oats; P. polycephalum recreated almost exactly – except that the slime mold version was more resistant to damage, where if the connection was broken, the rest of the web could continue.
Another team of researchers found that protists can effectively solve the traveling salesman probleman exponentially complex mathematical problem that programmers routinely use to test algorithms.
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Earlier this year, a team of researchers discovered that P. polycephalum can “remember” where it is previously found food based on the structure of the veins in that area. This follows previous research by Dussutour and her colleagues, who found that slime mold stains can learn and remember substances that they didn’t like and pass that information on to other clumps of slime mold when they merge.
“I’m still amazed at how complex they are, in a way, because they always surprise you in an experiment, they would never do what you choose,” Dussutour said.
In one case, her team tested a growth medium used for mammalian cells and wanted to see if slime would like it.
“That hated that. He started building this strange three-dimensional structure so he could take the lead and escape. And I’m like, ‘Oh my God, this organism.'”
Although technically a single-celled organism, P. polycephalum it is considered a network that exhibits collective behavior. Each part of the slime mold works independently and shares information with neighboring parts, without centralized processing.
“I guess the analogy would be neurons in the brain,” Reid said. “You have this one brain that’s made up of many neurons—it’s the same with slime mold.”
– Audrey Dussutour (@Docteur_Drey) April 3, 2021
That brain analogy is really intriguing and wouldn’t be the first time P. polycephalum was compared to a neural network. The topology and structure of brain networks and slime mold patches are very similar, and both systems exhibit oscillations.
It is not entirely clear how information is propagated and shared in the slime mold, but we know that P. polycephalumveins contract to act as a peristaltic pump, forcing cytoplasmic fluid from compartment to compartment. And the oscillations in this fluid seem to coincide with encounters with external stimuli.
“These oscillations are thought to transmit information, process information, how they interact and actually produce behavior at the same time,” Döbereiner told ScienceAlert.
“If you have a network Physarum it goes to a certain food, it changes its oscillation pattern when it encounters sugar: it starts to oscillate faster. Because of these faster oscillations, the whole organism begins to change its oscillation pattern and begins to flow in the direction where the food is found.”
He and colleagues published a paper in 2021 showing that these oscillations are remarkably similar to the oscillations seen in the brain, except that it is a hydrodynamic system rather than electrical signals.
“What’s relevant is not so much what oscillates and how information is transmitted,” he explains, “but that it oscillates and that the topology is relevant—whether one neuron is connected to 100 neurons or just two; is the neuron connected only to its neighbors or is it connected to another neuron that is very far away.”
As exciting as his escapades seem, any researcher who works with him will tell you that P. polycephalum it is not, per se, a brain. It is not capable of higher level processing or abstract reasoning, as far as we can tell.
Nor, as intriguing as the notion may seem, is it likely to evolve into something like a brain. The organism has had a billion years to do this and shows no signs of moving in that direction (though if some science fiction writers like the idea, feel free to go with it).
In terms of overall biology, slime mold is extremely simple. And by that very fact, it changes the way we understand problem solving.
Like other organisms, it needs food, it needs to navigate its environment and it needs a safe place to grow and reproduce. These problems can be complex, but still P. polycephalum it can solve them with its extremely limited cognitive architecture. It does so in its own simple way and with its own limitations, Reid said, “but that in itself is one of the beautiful things about the system.”
In a way, it leaves us with an organism—a moist, slimy, moisture-loving blob—whose cognition is fundamentally different from our own. And, just like the Tokyo subway, it can teach us new ways to solve our own problems.
“It teaches us about the nature of intelligence, it actually challenges certain views and basically expands the concept,” Reid said.
“It forces us to challenge these long-held anthropocentric beliefs that we are unique and capable of so much more than other creatures.”
A version of this article was first published in June 2021.
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