Decision-making without a brain: How an amoeboid organism solves the two-armed bandit

Chris R. Reid*, Hannelore MacDonald, Richard P. Mann, James A R Marshall, Tanya Latty, Simon Garnier

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    68 Citations (Scopus)
    121 Downloads (Pure)


    Several recent studies hint at shared patterns in decision-making between taxonomically distant organisms, yet few studies demonstrate and dissect mechanisms of decision-making in simpler organisms. We examine decision-making in the unicellular slime mould Physarum polycephalum using a classical decision problem adapted from human and animal decision-making studies: the two-armed bandit problem. This problem has previously only been used to study organisms with brains, yet here we demonstrate that a brainless unicellular organism compares the relative qualities of multiple options, integrates over repeated samplings to perform well in random environments, and combines information on reward frequency and magnitude in order to make correct and adaptive decisions. We extend our inquiry by using Bayesian model selection to determine the most likely algorithm used by the cell when making decisions. We deduce that this algorithm centres around a tendency to exploit environments in proportion to their reward experienced through past sampling. The algorithm is intermediate in computational complexity between simple, reactionary heuristics and calculation-intensive optimal performance algorithms, yet it has very good relative performance. Our study provides insight into ancestral mechanisms of decision-making and suggests that fundamental principles of decision-making, information processing and even cognition are shared among diverse biological systems.

    Original languageEnglish
    Article number20160030
    Pages (from-to)1-8
    Number of pages8
    JournalJournal of the Royal Society Interface
    Issue number119
    Publication statusPublished - 1 Jun 2016

    Bibliographical note

    Copyright the Author(s) 2016. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


    • slime mould
    • Physarum polycephalum
    • decision-making
    • exploration – exploitation trade-off
    • Bayesian model selection
    • two-armed bandit


    Dive into the research topics of 'Decision-making without a brain: How an amoeboid organism solves the two-armed bandit'. Together they form a unique fingerprint.

    Cite this