Study

Habituation in non-neural organisms: evidence from slime moulds

Boisseau, Romain P.; Vogel, David; Dussutour, Audrey

Proceedings of the Royal Society B, 2016

Peer-reviewedcontrolled laboratory experimentlaboratory

What they did

Plasmodia had to cross a bridge containing a bitter but harmless substance — quinine or caffeine — to reach food. Crossing time was measured daily over several days, alongside controls on a plain bridge, and recovery was tested after a period without exposure.

Studied in: Physarum polycephalum
Sample size: 2000 plasmodium trials across treatment groups

What they found

Plasmodia initially crossed slowly and then progressively faster, reaching control speed after several days. The change was specific to the substance experienced, did not transfer to a different bitter compound, and was lost after two days without exposure — the diagnostic signature of habituation rather than fatigue or sensory adaptation.

What it means

The authors' reading, and ours. Where they differ, that difference is the point.

How the authors put it

A single-celled organism with no nervous system meets the behavioural criteria for habituation, the simplest form of learning.

How NatureHQ reads it

This is a stronger result than the maze, and less famous. Habituation has a formal definition with control conditions attached — stimulus specificity and spontaneous recovery — and the experiment tests them rather than asserting the conclusion. It is evidence that learning does not require neurons; it is not evidence of intelligence, memory in any rich sense, or a mind.

Limitations

One species under laboratory conditions with a single class of stimulus.
Habituation is the simplest learning phenomenon and implies nothing about higher cognition.
The cellular mechanism is unidentified.