#SlimeMold #memory #consciousness

"Memories without brains

Certain slime moulds can make decisions, solve mazes and remember things. What can we learn from the blob?

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The differences between P polycephalum and humans may seem vast, but slime mould can reveal a remarkable amount about various aspects of how we remember. While many people might assume that our memories are primarily stored within our brains, some philosophers like myself argue that – along with some other aspects of cognition – memory can extend beyond the confines of the body to involve coupled interaction with structures in the environment. At least some of our cognitive processes, in short, loop out into our surroundings. Slime mould is an intriguing candidate to explore this idea because it doesn’t have a brain at all, yet in some cases can apparently ‘remember’ things without needing to store those associated memories within itself. In other cases, memories acquired via learning by one individual can even be acquired by a separate individual through physical contact. The behaviour of this strange form of life suggests that some of our ideas about how memories are acquired may need a rethink.

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Once on the verge of being forgotten, P polycephalum is now recognised as a valuable model organism in behavioral biology. Some researchers have even explored it as an unconventional computer, showing how it could perform processing tasks and mimic electronic components.

But how can an apparently simple organism like a slime mould remember?

Wherever they migrate, Physarum plasmodia leave behind extracellular slime trails – a non-living mucopolysaccharide. In the wild, you’d most commonly find these trails in areas that a slime mould has already foraged and, hence, which are depleted of food. In principle, encountering the stuff could therefore tell the slime mould something about the availability of food in the area – but is extracellular slime used as a memory trace?

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Reid and colleagues hypothesised that if Physarum uses extracellular slime as a memory trace of previously explored and likely food-depleted areas, then the plasmodia that encounter trails in the coated condition should take a significantly longer amount of time to reach the goal than in the blank condition. In the wild, an environmental record of an area already foraged and exhausted would be useful: it would tell a Physarum to look elsewhere. But with this particular experimental design, the researchers figured that fully coating the agar surface with extracellular slime would slow navigation because this uniformly coated surface would render the Physarum’s own slime trails largely undifferentiated and therefore useless. In contrast, plasmodia on blank surfaces could lay down and use their own distinct slime trails, creating a differentiated spatial map that allowed them to avoid revisiting previously explored areas.

And this is precisely what they found. Plasmodia in the coated condition took 10 times longer to reach the goal than the other plasmodia in the blank condition did. In this case, extracellular slime wasn’t exactly helping the organism, but it did show the researchers that it was using it as a memory trace."

https://aeon.co/essays/what-can-slime-mould-teach-us-about-biological-memory