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Physarum polycephalum. Credit: frankenstoen/WikipediaPhysarum polycephalum, or the “many-headed slime,” often makes its home in forest areas, coalescing into yellow blobs on moist tree trunks and decaying leaves when temperatures are cool. In the past, scientists have tested this brainless slime mold’s ability to exhibit intelligence. Amazingly, it’s been prompted to solve mazes when teased with oats, and has exhibited the ability to anticipate periodic events.

Scientists from France’s Toulouse University are continuing this research, and have discovered that the slime mold can learn to avoid unsavory compounds.

The research was published in Proceedings of the Royal Society B.

“What’s interesting about slime molds is they appear to be simple, because there is only one cell, but they are capable of amazing stuff, things that we thought were only possible with nervous systems or brains,” said study author Romain Boisseau to the Los Angeles Times.   

The research team focused on habituation, a form of learning where an organism’s responses to a repeated stimulus change.

In the experiments, the researchers placed a petri dish of “many-headed slime,” grown in agar gel, nearby a petri dish with oats and agar gel. When the dishes were connected by a bridge of agar gel, the slime mold usually crossed over to the oat petri dish in roughly two hours.

The slime accomplishes mobility by crawling with temporary projections called pseudopods.

Then, the researchers covered part of the bridge with either caffeine or quinine, making it bitter. Initially, the slime mold avoided the polluted areas and took nearly three times as long to cross the bridge.

However, the organism “learnt to ignore quinine or caffeine when the stimuli were repeated,” the researchers wrote.

By the sixth day, Boisseau told the Los Angeles Times the slime mold acted as if the caffeine and quinine were no longer present on the bridge.             

When the deterrent compound was removed, the slime mold reverted back to its original behavior. 

“Our results meet the principal criteria that have been used to demonstrate habituation: responsiveness decline and spontaneous recovery,” the researchers wrote.

Additionally, the researchers found that the quinine-exposed slime when exposed to caffeine had to learn how to deal with the new compound, and vice-versa for the caffeine-exposed slime. This demonstrates stimulus specificity.

“Our results point to the diversity of organisms lacking neurons, which likely display a hitherto unrecognized capacity for learning,” the researchers wrote.   

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