Slime moulds use external 'memory' to navigate: study

Researchers in Australia found that the slime mould could navigate around a U-shaped maze to a food source, using their slimy deposits, the BBC Nature reported.

"A slime mould is not a fungus or mould, but is in fact a protist, which is really the odds and ends of the natural world that don't fit in with the rest of our taxonomic grouping system," Christopher Reid from the University of Sydney who led the study, said.

Researchers placed the organism, which Reid described as a "large, blob-like cell", on one side of a dish of agar gel.

On the other side, researchers placed a sugary food source that they knew the slime mould would be attracted to.

In a test more commonly used to analyse the artificial intelligence of robots, they placed a U-shaped trap between the slime mould and its food source to understand how the organism moved around its environment.

"The whole organism is made up of bits of pulsating tissue, which are constantly expanding and contracting, using a similar mechanism to our own muscle cells," explained Reid.

"Each part changes the speed at which it pulsates according to what it can sense in the environment around it - for example food, light or heat - which are detected by chemical receptors on the cell's surface," he added.

"The pulsating parts are also influenced by the throbbing of their neighbours within the cell, which means that they can communicate with each other, to pass information through the organism about what is happening in the environment outside. The different speeds of contraction directly influence which direction the cell will then move in," Reid said.

Researchers observed the slime mould exploring the dish, leaving a trail of slime behind wherever it went.

According to the scientists, this slime trail was key to the organism's path-finding because it acted like a trail-marker, comparable to Hansel and Gretel's trail of breadcrumbs.

They found that the slime mould did not revisit areas it had already investigated.

"In essence, the slime mould is memorising where it has been - storing this memory in the external environment and recalling the information when it later touches the slime-coated area," Reid told the BBC.

Of the moulds tested, 96 per cent successfully found their way to the sugary substance, taking on average 57 hours to do so. However, when researchers covered the whole dish in slime only 33 per cent were able to reach their goal within the 120-hour time limit.

"Without the benefit of memory, the slime moulds spent almost 10 times longer pointlessly re-exploring areas they had been before," said Reid.