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Brainless slime molds may have memory systems

Researchers at the University of Sydney have found that brainless slime molds have memory systems. According to a university report, brainless slime molds use excreted chemicals as a memory system. Researchers say that the finding supports the theory that an external spatial memory was the first step in the evolution of memory.

“We have shown for the first time that a single-celled organism with no brain uses an external spatial memory to navigate through a complex environment,” said Christopher Reid from the University of Sydney’s School of Biological Sciences in a statement. “Our discovery is evidence of how the memory of multi-cellular organisms may have evolved – by using external chemical trails in the environment before the development of internal memory systems.”

According to the researchers, the experiment was inspired by robots programmed to react only to feedback from their external environment to deal with obstacles. Slime molds, researchers say, also use “reactive navigation” to navigate.

The researchers tested their theory by asking the slime mold to finding its way out of a U-shaped barrier. As the slime mold explores its environment, it leaves behind a trail of extracellular slime. The brainless mold uses the extracellular slime to stay away from areas that it has already investigated.

“Results from insect studies, for example ants leaving pheromone trails, have already challenged the assumption that navigation requires learning or a sophisticated spatial awareness. We’ve now gone one better and shown that even an organism without a nervous system can navigate a complex environment, with the help of externalized memory,” said Mr. Reid.

The researchers contend that in simple environments chemical trails are not necessary for effective navigation but in more complex environments the unique navigation system helps the brainless slime mold overcome obstacles.

The findings were recently published in the journal Proceedings of the National Academy of Sciences.