The 90-Minute Bell: How Slime Molds Sense the Passage of Time

Does a single-celled organism have a sense of time? For humans, time is a complex construction of the brain, tracked by circadian rhythms and hippocampal clocks. But in 2008, a team of researchers at Hokkaido University discovered that the slime mold Physarum polycephalum can “clock” regular events and anticipate them with surprising accuracy.

This phenomenon, often referred to as the 90-Minute Bell, proves that memory and anticipation can exist in a bag of fluid, without a single neuron.

The Cold Zap Experiment

In the landmark study, scientists exposed a slime mold to a series of sudden, stressful changes in its environment. Every 30 to 60 minutes (intervals varied by experiment), they would subject the blob to a “cold zap”—a sudden drop in temperature and humidity.

• The Immediate Reaction: The blob, which hates cold and dryness, would immediately slow down its crawling to conserve energy and preserve its internal moisture.
• The Routine: The researchers repeated this interval many times, creating a predictable rhythm of stress.

The Moment of Anticipation

The real shock came when the researchers stopped the cold zaps. Even though the environment remained warm and humid, the slime mold continued to slow down its movement at the exact same intervals where the cold zap should have occurred.

The organism had created a “temporal expectation.” It was predicting a future threat based on its memory of past events. It had learned the rhythm of its environment.

How Can Goo Keep Time?

Since the blob has no brain to process time, how does it “count” the minutes? The leading theory focuses on the Oscillatory Rhythms of its own body.

1. Chemical Pulsing: The blob’s internal fluid (cytoplasm) pulses back and forth in a rhythmic cycle (shuttle streaming).
2. Rhythm Entrainment: Just like a pendulum or a metronome can be synchronized by external vibrations, the internal chemical pulses of the blob can be “entrained” (tuned) by external stress.
3. The Biological Metronome: The blob isn’t “counting seconds”; it is experiencing a physical shift in its internal chemistry that acts like a biological metronome. The frequency of its pulsing shifts to match the frequency of the environmental threat.

The “Memory” Decay

Like all memories, the blob’s sense of the “90-minute bell” isn’t permanent. If the environment remains stable for long enough, the entrained rhythm begins to fade, and the blob returns to its normal, unstructured exploration. However, if a single zap is reintroduced after a long break, the blob can “remember” the old rhythm much faster than it learned it the first time.

Conclusion: A Primal Clock

The ability to sense time is a fundamental survival skill. By predicting when a forest floor might dry out or when a predator might be active, the slime mold has used its biological “bell” to survive for 600 million years. It teaches us that time-keeping is not a high-level brain function; it is a fundamental property of moving, pulsing life.

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Fascinated by biological clocks? Read our guide on Slime Mold Foraging Patterns.

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Origin and E-E-A-T

• Source: SciShow: “Slime Mold: A Brainless Blob that Seems Smart.”
• Key Study: Saigusa, T., et al. (2008). Physarum can anticipate periodic events.
• Scientific Context: Temporal Entrainment in non-neuronal organisms.