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Rapid Online Changes of Mind during Value-based Action Decisions

While the principles of decision-making are often expressed in terms of benefit-cost trade-off, reasonable doubt remains as to how the cognitive value and motor cost associated to several options may be computed across several brain areas, ultimately leading to a decision. Furthermore, does the assessment of non-chosen options continue after the decision has been made and the selected movement is already ongoing? Does the planning of several motor options depend on a unique parallel process or are there some elements within the sensorimotor loop requiring a sequential processing? Our hypothesis is that a change of available prospects at any point in time should dynamically adjust the desirability for each option, implying a fast reassessment of values and costs across prefrontal and motor cortical areas, even after an initial decision has been made and its associated response movement is ongoing. To test this, we performed a decision-making task in which human participants were instructed to select a reaching path trajectory from an origin to a wide rectangular target to gain the most reward. Reward delivery was contingent upon the distribution of value and upon precise target arrival. The original value distribution was altered during the ongoing movement in one third of the trials. Our results show that participants changed their movement trajectories towards the target position offering a better prospect, as presented by the second distribution. The changes of mind occurred more frequently for slow movements, had a duration in average inferior to the reaction time, and altered the initial timing and movement velocity. Although reward is the main factor guiding the selection of a specific movement in our experiment, our results indicate that the motor system was biased towards early changes of mind, given that the amplitude of the first acceleration and velocity peaks was significantly smaller in trials in which the participant switched target side and those in which they stuck to their original choice. Finally, the short latency of the recorded changes of mind strongly supports the hypothesis that, for the experimental conditions hereby considered, value considerations occur in parallel to motor planning.