Parameter-dependent shift from rational to irrational decisions in mice

In the classical view of economic choices, subjects make rational decisions evaluating the costs and benefits of options in order to maximize their overall income. Nonetheless, subjects often fail to reach optimal outcomes. The overt value of an option drives the direction of decisions, but covert factors such as emotion and sunk cost are thought to drive the observed deviations from optimality. Many questions remain to be answered as to 1) which contexts contribute the most to deviation from an optimal solution; and 2) the extent of these effects. In order to tackle these questions, we devised a decision-making task for mice, in which cost and benefit parameters could be independently and flexibly adjusted and for which a tractable optimal solution was known. Comparing mouse behavior with this optimal solution across parameter settings revealed that the factor most strongly contributing to suboptimality was the cost parameter. The quantification of sunk cost, a covert factor implicated in our task design, revealed it as another contributor to suboptimality. In one condition where the large reward option was particularly unattractive and the small reward cost was low, the sunk cost effect and the cost-led suboptimality almost vanished. In this regime and this regime only, mice could be viewed as close to rational. Taken together, our findings support a model whereby parallel neural circuits independently activate and modulate multiple valuation algorithms, and suggest that "rationality" is a task-specific construct even in mice. Significant StatementIrrational factors in economic decision-making often cause significant deviation from optimal outcomes. By devising a flexible economic choice behavior for mice and comparing their behavior with an optimal solution, we investigated overt and covert factors that contributed to suboptimal outcomes and quantified the deviation from optimality. This investigation identified regimes where mice could be viewed as rational or irrational depending upon the parameters in the same task. These findings may provide a platform to investigate biological substrates underlying rational and irrational decision factors.