Decision-making without a brain: how an amoeboid organism solves the two-armed bandit.
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.
Department of Biological Sciences, New Jersey Institute of Technology, Newark, NJ 07102, USA chrisreidresearch@gmail.com.
Chris R
CR
Reid
Department of Biological Sciences, New Jersey Institute of Technology, Newark, NJ 07102, USA.
Hannelore
H
MacDonald
School of Mathematics, University of Leeds, Leeds LS2 9JT, UK.
Richard P
RP
Mann
Department of Computer Science, University of Sheffield, Sheffield S1 4DP, UK Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.
James A R
JA
Marshall
School of Life and Environmental Sciences, University of Sydney, Sydney, New South Wales 2006, Australia.
Tanya
T
Latty
Department of Biological Sciences, New Jersey Institute of Technology, Newark, NJ 07102, USA.
Simon
0000-0002-3886-3974
S
Garnier
D001499:Bayes Theorem; D003657:Decision Making; D008954:Models, Biological; D016839:Physarum polycephalum / Q000502:physiology*
Bayesian model selection; Physarum polycephalum; decision-making; exploration–exploitation trade-off; slime mould; two-armed bandit