This bizarrely clever, creeping slime is redefining how we understand intelligence: ScienceAlert
Imagine that you are walking through a forest and you roll your foot over a tree trunk. At the bottom, something moist and yellow spreads out – kind of like something you might have sneezed out… if that was something banana yellow spreading out into elegant fractal branches.
What you would see is the plasmodium form of Physarum polycephalum, the many-headed slime mold. Like other slime molds found in nature, it fulfills an important ecological role, aiding the decay of organic matter to recycle it into the food web.
This bizarre little organism has no brain or nervous system; its blobby, bright yellow body is just one cell. This slime mold species has thrived, more or less unchanged, in its damp, decaying habitats for a billion years.
And over the past 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 could communicate with each other,” says biologist Audrey Dussutour of the French National Center for Scientific Research.
“Even these little microbes can learn. It gives you a little bit of humility.”
P. polycephalum – adorably nicknamed “The Blob” by Dussutour – isn’t exactly rare. It can be found in dark, moist, cool environments such as the leaf litter on a forest floor. It’s also very peculiar; although we call it a ‘mold’, it is actually not a fungus. Nor is it an animal or plant, but a member of the protist kingdom – a sort of gathering group for anything that cannot be neatly classified into the other three kingdoms.
It begins its life as many individual cells, each with a single nucleus. Then they fuse together to form the plasmodiumthe vegetative stage of life in which the organism feeds and grows.
In this form, fanning out in veins to search for food and explore its environment, it is still a single cell, but with millions or even billions of nuclei swimming in the cytoplasmic fluid locked in the bright yellow membrane.
Cognition without a brain
Like all organisms, P. polycephalum must be able to make decisions about its environment. It must seek food and avoid danger. It must find the ideal conditions for its reproductive cycle. And this is where our little yellow friend gets really interesting. P. polycephalum has no central nervous system. It doesn’t even have specialized tissues.
“We’re talking about cognition without a brain, of course, but also without neurons. So the underlying mechanisms, the whole architectural framework of how it handles information, is completely different from the way your brain works,” Macquarie University biologist Chris Reid said in a statement. Australia told ScienceAlert in 2021.
“By bringing it the same problem-solving challenges that we’ve traditionally given animals with brains, we can begin to see how this fundamentally different system could come to the same result. It’s where it becomes clear that for many of these things – which we always thought they needed a brain or some sort of higher information processing system — that’s not always necessary.”
P. polycephalum is known to science. Decades ago, as physicist Hans-Günther Döbereiner of the University of Bremen in Germany explained, it was the “workhorse of cell biology.” It was easy to clone, save and study.
As our genetic analysis toolkits evolved, organisms such as mice or cell lines such as HeLa took over, and P. polycephalum fell by the wayside.
In 2000, biologist Toshiyuki Nakagaki of RIKEN in Japan pulled the little creature out of retirement – and not for cell biology. his paper, published in Naturewas titled “Maze solving by an amoeboid organism” – and that’s exactly what P. polycephalum had done.
Nakagaki and his team had placed a piece of plasmodium, a food reward (oats, because P. polycephalum Loves oat bacteria) on the other, and watched what happened.
The results were astonishing. This weird little acellular organism managed to find the fastest route through every maze thrown at it.
“That sparked a wave of research into other kinds of more difficult scenarios that allow us to test the slime mold,” Reid said.
“Almost all of them were somehow surprising and surprised the researchers in how the slime mold actually performed. 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 to and which are thought to be the domain of higher organisms.”
Full of surprises
Nakagaki recreated the Tokyo subway, with the station nodes marked with oats; P. polycephalum i made it almost exactly – except the slime mold version was more robust to damage, with if a link was broken the rest of the network could continue.
Yet another team of researchers found that the protist could efficiently solve the traveling salesman probleman exponentially complex mathematical task that programmers routinely use to test algorithms.
Earlier this year, a team of researchers found that: P. polycephalum can “remember” where it is previously found food based on the structure of the veins in that area. This followed earlier research by Dussutour and her colleagues, who found that blobs of slime mold learning and remembering materials that they didn’t like, and pass that information on to other blobs of slime mold once they’ve fused.
“I’m still amazed at how complex they are, because they always surprise you in an experiment, they would never do exactly what you want to do,” Dussutour said.
In one case, her team tested a growth medium used for mammalian cells and wanted to see if the mucus would like it.
“It hated the. It started to build this strange three-dimensional structure so that it could take the lead and escape. And I’m like, ‘Oh my god, this organism’.”
A processing network
Although it is technically a unicellular organism, P. polycephalum is regarded as a network that exhibits collective behaviour. Each part of the slime mold works independently and shares information with the adjacent sections, without centralized processing.
“I think the analogy would be neurons in a brain,” Reid said. “You have this one brain that’s made up of many neurons — the same goes for the slime mold.”
— Audrey Dussutour (@Docteur_Drey) April 3, 2021
That brain analogy is really intriguing, and it wouldn’t be the first time P. polycephalum has been compared to a network of neurons. The topology and structure of brain networks and slime mold blobs are very similar, and both systems exhibit oscillations.
It’s not entirely clear how information is disseminated and shared in the slime mold, but we do know P. polycephalumThe veins contract to act as a peristaltic pump, pushing cytoplasmic fluid from section to section. And oscillations in this fluid seem to coincide with encounters with external stimuli.
“It’s thought that these oscillations convey information, process information, by the way they interact and produce the behavior at the same time,” Döbereiner told ScienceAlert.
“If you have a network of Physarum When it comes to a particular food, the oscillation pattern changes when it encounters sugar: it starts to oscillate faster. Because of these faster oscillations, the whole organism starts to change its oscillation pattern and starts flowing in the direction where the food was found.”
Him and colleagues published a paper in 2021, showing that these oscillations are extremely similar to the oscillations seen in a brain, only a hydrodynamic system rather than electrical signals.
“What’s relevant isn’t so much what oscillates and how the information is transported,” he explains, “but that it oscillates and that a topology is relevant — is one neuron connected to 100 neurons or just two; is a neuron connected alone? with its neighbors or is it connected to another neuron very far away.”
As exciting as the escapades seem, any researcher who works with them will tell you so P. polycephalum is not a brain in itself. It is incapable of higher-level processing or abstract reasoning, as far as we can tell.
It’s also unlikely, however intriguing the idea may seem, to grow into anything like a brain. The organism has had a billion years to do this and shows no signs of moving in that direction (although if there are any science fiction writers who like the idea, feel free to get on with it).
In terms of general biology, slime mold is extremely simple. And that is precisely why it changes how we understand problem solving.
Like other organisms, it needs food, needs to navigate its environment, and needs a safe place to grow and reproduce. These issues can be complex, and yet P. polycephalum can solve them with its extremely limited cognitive architecture. It does that in its own simple way and with its own limitations, Reid said, “but that in itself is one of the great things about the system.”
In a way, it leaves us with an organism — a wet, slimy, moisture-loving blob — whose cognition is fundamentally different from our own. And like the Tokyo subway, it can teach us new ways to solve our own problems.
“It teaches us about the nature of intelligence, really, it challenges certain notions and actually broadens 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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