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No brain? No problem! This mold makes navigation decisions in a thought process


Having a brain can be a big advantage. Of course, you have to put in a lot of energy to make it work properly, but it unlocks all kinds of cognitive processes that just wouldn’t be possible otherwise. Or… would they do it?

In a new study, researchers have shown that a brainless slimy mold uses its body to sense mechanical signals in the environment and performs calculations similar to what we would call thinking to decide which direction to go.

Image credits: Jerry Kirkhart.

Extraordinary mussels and how to study them

P. polycephalum is a strange creature. It is not an animal, nor a plant, nor a mushroom. It is a protist, which means pretty much any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. Seriously, that’s what his Wiki page says.

But it gets even stranger. P. polycephalum is actually cell-free – meaning it has no cells, at least in the stage of plasmodial life. His main work is the decomposition of organic matter, especially in dark and humid environments like forest soils.

Researchers have done some pretty crazy things with P. polycephalum. For example, a team of Japanese and Hungarian researchers have shown that this mold can solve the shortest path problem. They grew mold in a maze with food (oatmeal) at both ends of a maze and the mold retracted from all over the maze except for the shortest path connecting the two places. It can even solve more complex navigation problems, sometimes with a precision rivaling that of modern computers. The point is (as you may have already understood) that P. polycephalum has no brain. However, he is able to learn and navigate very well in his environment.

“People are more and more interested Physarum because it doesn’t have a brain, but it can still perform many of the behaviors we associate with thinking, ”said neuroscientist Nirosha Murugan of Algoma University in Canada.

“Finding out how proto-intelligent life does this kind of calculation gives us a better insight into the foundations of cognition and behavior in animals, including our own. “

Normally, in this type of study, the mold receives an incentive in the form of a food or chemical signal, but in this case, the researchers more or less left it on its own. They placed samples in the center of Petri dishes covered with agar gel, placed a glass disc on one side and three small discs on the other. They then allowed the organisms to grow freely over the next 24 hours, following their growth patterns.

This time-lapse series of photos shows a Physarum specimen growing in a generalized “buffering” pattern for about 13 hours, then extending a long growth to the side of the dish with three discs. Credit: Nirosha Murugan, Levin lab, Tufts University and Wyss Institute at Harvard University.

During the first 12 hours, the slime mold grew evenly in all directions. But after 12-14 hours he started to make decisions. About 70% of the time, it extended a long branch that grew on the surface of the gel towards the three discs. He also made a remarkable decision: he chose to expand towards the three discs instead of one, without actually exploring the area to confirm what was happening.

The researchers then tried to figure out how (and why) it did this.

Redefining Thinking

The researchers tried to experiment with different configurations. For the most part, the mud would go towards the three disks – until the researchers stack the three disks on top of each other. When they did that P. polycephalum lost its ability to sail towards the larger mass and grew roughly equally on both sides.

So the mold wasn’t using the total mass to direct its navigation, that was something else. It turns out that something was a slight deformation of the semi-flexible gel at the bottom of the petri dish. In other words, the three discs distorted the lower gel more than the single disc, and the mold used this to direct its navigation towards what it saw as a greater potential reward. In other words, this strange brainless creature wasn’t just drifting towards the first big thing she perceived around her – she was making a calculated decision on where to grow based on the stress patterns she saw. detected in its environment.

“Imagine you are driving on the freeway at night and looking for a city to stop. You see two different arrangements of light on the horizon: a single bright spot and a group of dim spots. While the single dot is brighter, the cluster of dots illuminates a larger area which is more likely to indicate a city, and therefore you are heading there, ”said co-author Richard Novak, Ph.D., chief personnel engineer at the Wyss Institute. “The light models in this example are analogous to the mechanical stress models produced by different mass arrangements in our model. Our experiments confirmed that Physarum can physically detect them and make decisions based on patterns rather than just signal strength.

Researchers still don’t know exactly How? ‘Or’ What he felt it, but mechanisms describing this type of sensory ability have been shown in previous studies. What is perhaps the most exciting thing here is the mold’s ability to use simple inputs and cellular mechanisms to make decisions.

“With most animals, we can’t see what changes inside the brain as the animal makes decisions. Physarum offers a truly exciting scientific opportunity as we can observe its decisions on where to move in real time by watching how its shuttle streaming behavior changes, ”said Murugan.

For this type of ability to have evolved in such a simple creature, it would seem to suggest that intelligence is not as modern in evolutionary history as we thought. Since researchers have already argued that slime mold has evolved multiple times throughout the history of the planet, including over 500 million years ago, we may even have to redefine what it means. intelligence.

“Our discovery of the use of biomechanics by this slimy mold to probe and respond to its surrounding environment highlights how early this ability evolved in living organisms and how closely intelligence, behavior, and morphogenesis are intertwined. related. In this organism, which grows to interact with the world, its change of form is its behavior. Other research has shown that similar strategies are used by more complex animal cells, including neurons, stem cells, and cancer cells. This work in Physarum offers a new model to explore the ways in which evolution uses physics to implement primitive cognition that determines form and function, ”said corresponding author Mike Levin, at Tufts University.

Oh by the way, did I mention that he can not only think, but he can also learn and pass on his experience?

The study was published in Advanced materials.

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