Original title: Exposure to paired blue light and nutrient alters aversive responses in Physarum polycephalum
Qiuran Wang, Niels Gaspers, Tobias Schlicht, Liberty Severs · September 2026
Can organisms without brains learn by association? Scientists debate whether simple creatures can connect two different cues. To find out, researchers studied Physarum polycephalum, an acellular slime mould. Normally, blue light repels this slime mould. It slows its movement and causes wider, less direct growth. The scientists trained the slime mould across up to four sessions by pairing the unpleasant blue light with food, using an oat. Later, they tested the slime mould with blue light alone. Trained moulds reached the lit area more often and with shorter latencyThe time it takes for the organism to start moving toward something after the test begins., meaning they arrived faster than untrained controls. Experiencing food alongside blue light reduced their avoidance. However, this response did not grow stronger with more training sessions. Because of this, the researchers cannot confirm that true associative learningLearning that links two separate events, like pairing a bell with food. caused the change.
Imagine you walk through a dark alley every day, and each time you find a $20 bill. At first you avoid the alley because it's dark and scary. But after finding money there repeatedly, you start walking through it more quickly and willingly. You still get a little nervous, but the dark alley now signals a reward. In this paper the dark alley is blue light, the money is food, and the slime mould adjusts its behavior because the two keep appearing together.
For over a century, learning required a nervous system. This work shows a slime mould with no neurons weakens its avoidance of blue light after repeatedly finding food there. If a single cell can form even temporary associations, it challenges how we define learning itself and opens questions about memory in any living system.
The abstract explicitly states that engagement did not strengthen with more pairings, and that multiple competing explanations exist—including non-associative processes like habituation or sensitization. Therefore the study cannot attribute the behavioral change to associative learning. It does not establish a general learning mechanism in Physarum, only that co-presentation of nutrient and aversive stimulus can relax avoidance under this specific protocol.
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Exposure to paired blue light and nutrient alters aversive responses in Physarum polycephalum — Qiuran Wang, Niels Gaspers, Tobias Schlicht et al. — bioRxiv — doi:10.64898/2026.09.09.750388
Abstract licence: CC BY
Explanation generated by Synthesis from the abstract — it is not the original paper. This is a preprint, so it hasn't necessarily been peer reviewed.