Reward-dependent selection of feedback gains impacts rapid motor decisions

Expected reward is known to affect planning strategies through modulation of movement vigor. Strikingly, although current theories suggest that movement planning consists in selecting a goal-directed control policy, the influence of reward on feedback control strategies remains unknown. Here we investigated this question in three human reaching experiments. First, we varied the explicit reward associated with the goal target and found an overall increase in movement vigor for higher reward targets, highlighted by larger velocities, feedback responses to external loads, and background muscle activity. Then, assuming that larger feedback gains were used to reject perturbations, we sought to investigate whether this effect hindered online decisions to switch to a new target in the presence of multiple successful goals. We indeed observed idiosyncratic switching strategies dependent on both target rewards and movement vigor, such that the more vigorous movements were less likely to switch to a new goal following perturbations. To gain further insight into a causal influence of movement vigor on rapid motor decisions, we demonstrated that biasing the baseline activity and reflex gains by means of a background load evoked a larger proportion of target switches in the direction opposite to the background load associated with lower muscle activity. Our results highlight the competition between movement vigor and flexibility to switch target during movement. Significance statement Humans can modulate their movement vigor based on the expected reward. However, a potential influence of reward on feedback control has not been documented. Here we investigated reaching control strategies in different contexts associated with explicit rewards for one or multiple goals, while exposed to external perturbations. We report two strategies: reward could either invigorate feedback gains, or promote flexible switches between goals. The engagement of peripheral circuits in the modulation of feedback gains was confirmed by the application of a background load that biased feedback vigor directionally, which evoked differences in switching behavior in the opposite direction. We conclude that feedback vigor and flexible changes in goal are two competing mechanisms to be selected when one interacts with a dynamic environment. ### Competing Interest Statement The authors have declared no competing interest.