Carey, H. D. | bioRxiv Science

bioRxiv2022

Young adults use whole-body feedback to perceive small locomotor disturbances.

To prevent a fall when a disturbance to walking is encountered requires sensory information about the disturbance to be perceived, integrated, and then used to generate an appropriate corrective response. Prior research has shown that feedback of whole-body motion drives this corrective response. Here, we hypothesized that young adults also use whole-body motion to perceive locomotor disturbances. 15 subjects performed a locomotor discrimination task in which the supporting leg was slowed during stance every 8-12 steps to emulate subtle slips. The perception threshold of these disturbances was determined using a psychometrics approach and found to be 0.08 {+/-} 0.03 m/s. Whole-body feedback was examined through center-of-mass (CoM) kinematics and whole-body angular momentum (WBAM). Perturbation-induced deviations of CoM and WBAM were calculated in response to the two perturbation levels nearest each subjects perception threshold. Consistent with our hypothesis, we identified significantly higher perturbation induced deviations for perceived perturbations in sagittal-plane WBAM, anteroposterior CoM velocity, and mediolateral CoM position, velocity, and acceleration. Because whole body motion is not sensed directly but instead arises from the integration of various sensory feedback signals, we also explored local sensory feedback contributions to the perception of locomotor disturbances. Local sensory feedback was estimated through kinematic analogues of vision (head angle), vestibular (head angular velocity), proprioception (i.e., sagittal hip, knee, and ankle angles), and somatosensation (i.e., anterior-posterior & mediolateral center-of-pressure, COP). We identified significantly higher perturbation induced deviations for perceived perturbations in sagittal-plane ankle angle only. These results provide evidence for both whole-body feedback and ankle proprioception as important for the perception of subtle slip-like locomotor disturbances in young adults. Our interpretation is ankle proprioception is a dominant contributor to estimates of whole-body motion to perceive locomotor disturbances.

neuroscience↗

bioRxiv2021

Young Adults Recruit Similar Motor Modules Across Walking, Turning, and Chair Transfers

Moving about in the world during daily life requires executing and successfully shifting between a variety of functional tasks, such as arising from a chair or bed, walking, turning, and navigating stairs, etc. Moreover, moving about during daily life requires not only navigating between different functional tasks but also performing these tasks in the presence of mental distractions. However, little is known about underlying neuromuscular control for executing and shifting between these different tasks. In this study, we investigated muscle coordination across walking, turning, and chair transfers by applying motor module (aka muscle synergy) analysis to the Timed-Up-and-Go (TUG) test with and without a secondary cognitive dual task. We found that healthy young adults recruit a small set of common motor modules across the subtasks of the TUG test and that their composition is robust to cognitive distraction. Instead, cognitive distraction impacted motor module activation timings such that they became more consistent. This work is the first to demonstrate motor module generalization across multiple tasks that are both functionally different and crucial for healthy mobility. Overall, our results suggest that the central nervous system may draw from a "library" of modular control strategies to navigate the variety of movements and cognitive demands required of daily life. New & NoteworthyWe demonstrated that healthy young adults recruit a small set of motor modules across subtasks of the Timed-Up-and-Go test (i.e., walking, turning, and chair transfers). Moreover, we showed that motor module composition, but not activation timing, is robust to cognitive distractions. These results support the hypothesis that healthy young adults recruit from a "library" of motor modules and modulate their activation timing to meet the different mechanical and cognitive demands required to navigate daily life.

neuroscience↗