The findings point to an ancient evolutionary origin of associative learning, potentially predating multicellular nervous systems, and raise questions about cognition in simple organisms.

A unicellular organism, Stentor coeruleus, demonstrates associative learning by linking a weak tap with a subsequent strong tap, implying memory-like processing without a brain.

The study suggests the broader possibility that associative learning and memory-like processes may occur in unicellular life, challenging the idea that neurons are required for learning.

In experiments, Stentor initially habituates to repeated strong taps, showing progressively reduced contraction over a sequence of taps.

Gershman and colleagues hypothesize that calcium signaling through touch receptors, coupled with receptor modifications, could serve as a molecular switch to alter contractions and enable learning.

The proposed mechanism involves touch receptors permitting calcium influx and voltage changes; repeated stimuli may modify receptors to modulate contractions.

Researchers acknowledge that the exact memory storage mechanism in Stentor is not yet known, but receptor-level changes offer a plausible explanation.

Across about ten paired trials, the probability of immediate contraction after the weak tap first rose and then fell, indicating an association between the weak and strong stimuli.

The study included a habituation phase with repeated strong taps, followed by pairing a weak tap with a strong tap to test predictive learning.

When a weak tap (predictor) is paired with a subsequent strong tap, the weak tap increasingly signals the upcoming strong tap, demonstrating associative learning.

Experts highlight the significance for understanding how memory is stored in simple organisms and the implications for the evolution of learning and cognition.

The work positions Stentor as a model for non-neural learning, challenging the notion that brains and neurons are strictly necessary for learning.