Impact of motor task execution on an individual’s ability to mirror forearm positions

This work is motivated by our goal of determining why individuals with stroke are impaired when locating their arms in space. We assessed the ability of individuals without neurological impairments to mirror their forearms during various motor tasks so that we could identify baseline performance in an unimpaired population. Nine right-hand dominant participants without neurological impairments mirrored forearm positions bi-directionally (i.e., right forearm mirrors left forearm, vice versa) for three motor tasks (i.e., passive, passive/active, and active) and two position identification modes (i.e., mirroring to a position stored in working memory versus concurrently felt by the opposite arm). During each trial, the participant’s reference forearm moved to a flexion (77. 5 ^∘) or extension (102. 5 ^∘) position, and then, their opposite forearm mirrored the position of their reference forearm. The main finding across all tested conditions is that participants mirrored forearm positions with an average magnitude of error <6.3∘. When controlling their forearms’ movements (active motor task), participants mirrored forearm positions more accurately by up to, on average, 5. 7 ^∘ at the flexion location than at the extension location. Moreover, participants mirrored forearm positions more accurately by up to, on average, 3. 5 ^∘ when their forearms were moved for them rather than when they controlled their forearms’ movements. Task directionality and position identification mode did not significantly affect participant arm mirroring accuracy. These findings are relevant for interpreting in future work the reason why impairments occur, on similar tasks, in individuals with altered motor commands, working memory, and arm impedance, e.g., post-stroke hemiparesis.