Slime moulds work on computer games

Andrew Adamatzky of the aptly named Unconventional Computing Centre, at the University of the West of England, in Bristol, UK, points out that computing a polygon defining a set of planar points is a classical problem of modern computational geometry. He has turned to the slime mould to help with such computations and explains in the International Journal of Bio-Inspired Computation how the organism can help.

Adamatzky explains that the slime mould Physarum polycephalum has a complicated lifecycle with fruit bodies, spores, and single-cell amoebae, but in its vegetative, plasmodium, stage it is essentially a single cell containing many cell nuclei. The plasmodium can forage for nutrients and extends tube-like appendages to explore its surroundings and absorb food. As is often the case in natural systems, the network of tubes has evolved to be able to quickly and efficiently absorb nutrients while at the same time using minimal resources to do so.

"Plasmodium's foraging behaviour can be interpreted as computation," explains Adamatzky, "when data are represented by spatial configurations of attractants and repellents, and results by structures of protoplasmic network." In other words by cultivating plasmodium on a surface peppered with attractants and repellents it should be possible to grow a network of tubes that connect the attractant points and avoid the repellents while producing the most effective connectivity between the former.

Adamatzky has now grown P. polycephalum in plastic containers, on paper kitchen towels sprinkled with distilled drinking water and fed on oat flakes. Bizarrely, for the attractants the researchers found that the Valerian and hop extracts found in Kalms "natural" sleeping tablets work over relatively long distance as targets for the plasmodium's probing appendages. "When presented with a half-pill of the Kalms tablets the plasmodium propagates towards the pill and forms, with its protoplasmic tubes, a circular enclosure around the pill," he explains.

By contrast, the tablets also contain short-distance, but slowly diffusing components such as magnesium stearate, stearic acid and titanium dioxide as well as sucrose that seem to repel the appendages preventing plasmodium from spreading into areas where these substances are present. The combination of these two properties causes P. polycephalum to develop a network of protoplasmic tubes with a major tube approximating the polygon outlines by the attractant points in the Petri dish on which the slime mould is grown.

The research into how slime moulds compute is very much ongoing but, Adamatzky suggests that this latest step takes us another step towards a future parallel embedded computer processor that uses non-linear chemical media rather than standard components such as silicon chips to carry out computations. He also hints at the development and control of a self-navigating slime mould robot.