Short-term immobilization impairs pointing direction programming and early motor control processes

Short-term limb immobilization is a valuable method for studying the contribution of proprioception since it temporarily reduces sensory and motor inputs. While several studies have shown that immobilization impairs cognitive and sensorimotor processes, none have yet demonstrated how it could specifically impact the programming of movement direction. Here, participants (N = 32) made uncorrected pointing movements toward five visual targets located in different directions - but requiring constant amplitude - without benefiting from any visual feedback on the hand. Pointing was performed on two consecutive days by Control and Immobilized participants, the latter of whom had worn a splint on the right arm during this 24 h period. Results showed that immobilization increased the duration of movement planning (i.e., longer reaction time) necessary to specify hand-path direction. A greater counterclockwise directional bias was observed at peak acceleration in the Immobilized group and persisted until the uncorrected movement offset. These results suggest that immobilization impacts direction programming as well as early motor control processes. We argue that proprioception deprivation impairs the perception of limb position, leading to both slower and less accurate motor command selection. Overall, we interpret that the lack of proprioceptive feedback and efference copies may influence the accuracy of movement planning after 24 h of immobilization, possibly reflecting changes in processes related to internal model mechanisms.