How to think when you don’t have a brain
Even a form of brainless slime mould can make decisions about its next venture. What can it teach humans?
Ateam of US biologists has shown that even a brainless slime mould, Physarum polycephalum, can compute where to grow next based on mechanical cues.
“People are becoming more interested in Physarum because it doesn’t have a brain but it can still perform a lot of the behaviours that we associate with thinking, like solving mazes, learning new things and predicting events,” says Nirosha Murugan, first author on a paper in Advanced Materials.
The researchers put Physarum in the middle of petri dishes, filled with agar gel. They placed different numbers of glass discs at the edges of the dishes, either next to each other or stacked atop one another, theorising that the mould would be attracted to the heavier objects in the gel.
The moulds grew out in an even pattern initially, then extended branches towards the heavy glass.
Interestingly, the mould moved towards one glass disc and three stacked glass discs at the same rate, despite the stacked discs being heavier. Even more interestingly, the slime preferred to grow towards three discs sitting next to each other, instead of the single disc.
This indicated to the researchers that the mould was “calculating” where to move next, and using something other than weight alone to make its decisions.
“With most animals, we can’t see what’s changing inside the brain as the animal makes decisions. Physarum offers a really exciting scientific opportunity because we can observe its decisions about where to move in real-time by watching how its [intercellular] behaviour changes,” says Murugan.