Rational choice theory assumes optimality in decision-making. Violations of a basic axiom of economic rationality known as “Independence of Irrelevant Alternatives” (IIA) have been demonstrated in both humans and animals and could stem from common neuronal constraints. Here we develop tests for IIA in the nematode
Caenorhabditis elegans
, an animal with only 302 neurons, using olfactory chemotaxis assays. We find that in most cases
C. elegans
make rational decisions. However, by probing multiple neuronal architectures using various choice sets, we show that violations of rationality arise when the circuit of olfactory sensory neurons is asymmetric. We further show that genetic manipulations of the asymmetry between the AWC neurons can make the worm irrational. Last, a context-dependent normalization-based model of value coding and gain control explains how particular neuronal constraints on information coding give rise to irrationality. Thus, we demonstrate that bounded rationality could arise due to basic neuronal constraints.
Ample evidence shows that humans violate fundamental economic axioms. Yet, the neural mechanism underlying inconsistent (or irrational) choices remains obscure. Here, we aim to show that inconsistent choices could rise either due to value miscalculations or due to motor errors during task execution. We report the results from two independent behavioral and neuroimaging studies. Subjects completed a risky-choice task to test their inconsistency levels, followed by two novel tasks, designed to solely examine motor output. We recorded mouse trajectories during task execution and designed 34 features to analyze choice dynamics. We show that choice dynamics predict inconsistency levels, even when motor output was absent any valuation elements. In the neuroimaging study, we show that inconsistency is tied to noisy value computations in reward circuits, but at the same time, is also related to noisy neural motor dynamics. These findings suggest that (at least) two neural sources of noise contribute to inconsistent choice behavior.
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