Can you be intelligent without a brain?

15 September 2021
4 min read
15 September 2021
4 min read

Can you be intelligent without a brain? The answer is “in a certain sense, yes” and this is demonstrated by a strange organism that looks like yellowish gelatinous mould but that has nothing to do either with moulds or fungi… It is called Physarum polycephalum and it is related to amoebas, that is to say to those unicellular organisms without a precise form that advance in stagnant water extending arms similar to tentacles, called pseudopodia.

Physarum polycephalum is an organism formed by many amoebae fused into a single large cell with thousands of nuclei; it likes semi-darkness and humid environments and feeds on organic matter found in the undergrowth, amongst decaying foliage. It is therefore an organism that plays an important role in the recycling of nutrients. To the naked eye, it is difficult to perceive the movement of the Physarum because it is very slow: only an accelerated shot can show how the “mould” stretches out its pseudopodia in every direction in search of something to eat. This is why it is called polycephalum, a word that means “many heads”; in fact it is impossible to establish where this strange organism begins and ends. With its thousand arms, Physarum explores the environment and, when it finds food, wraps itself around it to absorb it one fragment at a time.

This “mould” is undemanding in terms of food and space, a few oat flakes and a dark, moist environment are all it needs to thrive even in the lab. Physarum is one of the organisms most widely studied in test tubes, observing its movements and… intelligence. It is a special form of intelligence, since this organism does not have a nervous system or even a brain. What, then, does its mind consist of? Physarum reacts to external stimuli, and this is not exceptional, as bacteria are also capable of this, but it is also able to remember, decide and teach. Here are a few examples.



Networks created by Physarum polycephalum.

In one experiment, between the mould and the oat flakes, researchers put some irritants: not dangerous, just annoying, like salt, which the mould really dislikes. Physarum stretched out its pseudopodia to reach its lunch but quickly withdrew them irritated by the salt. It tried again and again desisted. After a number of attempts, it understood that if it wanted to eat, it had to endure some discomfort, and so it did: it stretched out its arms and pounced on the food. When the researchers put a mould that had learned to ignore the salt barrier in contact with one that had never experienced it, they observed how the latter crossed the salt without ever flinching. This means that the first mould had “taught” the second mould that the salt tract was just an unpleasant nuisance.

Physarum dislikes cold. Japanese researchers cooled the mould for ten minutes every hour. Mould reacts to cold by slowing down movement. After a few hours, the researchers stopped tormenting the mould and observed that Physarum slowed down its movement every hour even though the temperature remained constantly comfortable: the mould had learned the pattern and anticipated the arrival of a new, unpleasant wave of cold.

In another lab, they put mould at the entrance to an intricate maze and placed an oat flake on the other side. The mould began to stretch out along the corridors in search of food, and when it found it, it reabsorbed the pseudopodia in the blind corridors, leaving only one arm active, the one that joined the central body and the food by the shortest path. This ability could be exploited to design electronic circuits or even to plan urban road networks. For example, to calculate the shortest route between two places in a city, it would be possible to allow mould to circulate in a miniature layout by placing food at the start and arrival: Physarium, without knowing it, would optimise the route by indicating the shortest path.

By Andrea Bellati