Slime Mold Intelligence

It challenges our fundamental understanding of cognition to suggest that a yellow, gelatinous blob found on decaying logs possesses intelligence. Yet, Physarum polycephalum, a single-celled organism with no brain and no nervous system, has proven capable of solving complex mathematical problems that take modern computers significant time to process.

Scientists are currently looking at this humble slime mold to redesign transport networks, evacuation routes, and supply chains. Here is how a brainless organism manages to outsmart human engineers and solve mazes with ruthless efficiency.

What is Physarum Polycephalum?

Before understanding how it solves problems, it is important to understand what this creature is. Physarum polycephalum is not a plant, animal, or fungus. It belongs to the kingdom of Protista. While it begins its life as microscopic individual cells, these cells eventually merge into a single, giant cell containing millions of nuclei.

This super-cell acts as a collective unit. In the wild, it hunts for bacteria and fungal spores on the forest floor. In the lab, however, researchers feed it oat flakes. Its primary drive is simple: find food, maximize nutrient intake, and conserve energy. This biological directive is what drives its problem-solving capabilities.

The Maze Experiment

The first major proof of slime mold intelligence came in 2000 from Toshiyuki Nakagaki at Hokkaido University in Japan. He and his team set up a simple maze. They placed the slime mold in the maze and placed oat flakes at the entrance and the exit.

The results were stunning:

1. Exploration: Initially, the mold spread itself thinly throughout every corridor of the maze to locate the food.
2. Optimization: Once it established contact with the food sources at both ends, it began to retract its body from the dead-ends.
3. Solution: It thickened the tube connecting the two food sources, creating a direct line.

The mold did not just find the food; it calculated the shortest possible physical route between the two points to maximize energy transfer. It effectively “solved” the maze by physically becoming the solution.

Redesigning the Tokyo Subway System

Nakagaki took his research further in 2010 with a more complex experiment that gained worldwide attention. He wanted to see if the slime mold could replicate the efficiency of the Tokyo rail system, a network that took human engineers decades of planning to perfect.

The experiment setup was specific:

• The main body of the slime mold was placed in the center of a petri dish (representing Tokyo).
• Oat flakes were placed around the dish in positions corresponding to major surrounding cities.
• Bright light was used to simulate mountains or lakes (obstacles), as the mold avoids light.

The Results

Within 26 hours, the slime mold expanded and connected to all the food sources. The network of tubes it created was almost mathematically identical to the actual Tokyo subway system.

The mold achieved a balance that engineers struggle with: efficiency versus resilience. It created thick, direct lines for main routes but also maintained thinner, redundant connections. If a researcher cut one of the tubes (simulating a rail line failure), the nutrients could still flow through the backup paths. The slime mold built a fault-tolerant network without a central planner.

How It Works: Thinking Without a Brain

Since the slime mold lacks neurons, it relies on physics and fluid dynamics to “think.” This process is known as shuttle streaming.

• Rhythmic Pulsing: The organism pushes cytoplasm (fluid containing nutrients) back and forth through its veins in a rhythmic pulse.
• Feedback Loops: When a section of the mold finds food, the pulsing speeds up in that area. This rapid pulsing widens the tube, allowing more fluid to flow.
• Atrophy: Conversely, parts of the mold that do not find food experience slower pulsing. These tubes eventually wither and die off.

External Memory

The slime mold also possesses a form of spatial memory. As it moves, it leaves behind a translucent trail of non-living slime. When the searching tendrils encounter this old trail, they sense it and turn away. This allows the organism to “remember” where it has already explored, preventing it from wasting energy searching the same empty area twice.

Future Applications

Researchers are now translating the biological rules of Physarum polycephalum into computer algorithms. This field, known as biologically inspired computing, is solving problems that are difficult for traditional binary computers.

• Urban Planning: Planners in the United States and Europe are using slime mold simulations to analyze highway density and evacuation routes for natural disasters.
• Space Exploration: Astronomers have used the “slime mold algorithm” to map the cosmic web, tracing the dark matter filaments that connect galaxies, as the structure is mathematically similar to the networks the mold builds.
• Bio-computing: Scientists are experimenting with using the mold itself as a biological computer chip, capable of processing sensory data and outputting logic commands.

Frequently Asked Questions

Is slime mold dangerous to humans? No. Physarum polycephalum is harmless to humans, animals, and plants. It feeds on bacteria, fungal spores, and decaying organic matter.

Can slime mold really learn? Yes, in a primitive sense. Experiments have shown that if you expose the mold to dry air (which it dislikes) at regular intervals, it will eventually begin to “brace” itself for the dry air at the expected time, even if you stop the stimulus. This suggests a form of anticipation or time-keeping.

How fast does it move? It is slow by human standards but fast for a fungus-like organism. It can move up to 4 centimeters per hour when it is hungry and detects a food source.

Where can I find this slime mold? It is common in damp, shady forests across North America and Europe. You can usually find it on the underside of rotting logs or in leaf litter. It often appears as a bright yellow, lace-like structure.