Integrated control of non-motor and motor efforts during decision between actions

Humans daily life is characterized by a succession of voluntary actions. Since energy resources are limited, the ability to invest the appropriate amount of effort for selecting and executing these actions is a hallmark of adapted behavior. Recent studies indicate that decisions and actions share important principles, including the exchange of temporal resources when the context requires it. In the present study, we test the hypothesis that the management of energy resources is shared between decision and action too. Healthy human subjects performed a perceptual decision task where they had to choose between two levels of effort to invest in making the decision, and report it with a reaching movement. Crucially, motor difficulty gradually increased from trial to trial depending on participants decision performance. Results indicate a relatively mild impact of the increasing motor difficulty on the choice of the non-motor (decision) effort to invest in each trial and on decision performance. By contrast, motor performance strongly decreased depending on both the motor and decisional difficulties. Together, the results support the hypothesis of an integrated management of energy resources between decision and action. They also suggest that in the context of the present task, the mutualized resources are primarily allocated to the decision-making process to the detriment of movements.