Sensorimotor incongruence alters limb perception and movement.

Altered limb ownership or heaviness has been observed in patients with hemiplegia, chronic pain, and several other conditions. Although these sensations are thought to be caused by sensorimotor incongruence, few studies have systematically verified this relationship. In addition, it remains unclear whether these subjective sensations affect movement execution. In a psychophysical experiment, we systematically investigated the relationships between sensorimotor integration and subjective limb perception, such as sense of ownership/heaviness, and verified the relationship between subjective limb perception and movement execution. Thirty-nine healthy participants were enrolled, and a visual feedback delay system was used to systematically evoke sensorimotor incongruence. Participants periodically flexed and extended their wrist while seeing a delayed image of their hand under five delay conditions (0, 150, 250, 350, 600ms). During wrist movement, electromyography (EMG) activity in flexor carpi radialis (FCR) was recorded. Also, to analyze the change in muscle activity and movement speed, the values of integral and peak frequency were calculated. To record changes in the subjective limb perception of the altered limb ownership and heaviness, we used a 7-point Likert scale for each participant. We found that altered ownership and heaviness increased with increasing feedback delay. Also, muscle activity and movement speed decreased with visual feedback delay. There was no significant correlation between subjective altered limb perception (i.e., altered limb ownership and heaviness) and muscle activity or movement speed. We systematically demonstrated that limb ownership, heaviness, muscle activation and movement speed were altered by sensorimotor incongruence. However, our study did not reveal the relationships between these factors. These results indicate the existence of different mechanisms governing subjective limb perception and movement execution. In the future, we should consider rehabilitation methods to improve sensorimotor incongruence.