Sensorimotor control of the trunk in sitting sway referencing

Abstract

We developed a sway-referenced system for sitting to highlight the role of vestibular and visual contributions to trunk control. Motor control was investigated by measuring trunk kinematics in the frontal plane while manipulating visual availability and introducing a concurrent cognitive task. We examined motor learning on three timescales (within the same trial, minutes), within the same test session (1 h), and between sessions (1 wk). Posture sway was analyzed through time-based measures [root mean square (RMS) sway and RMS velocity], frequency-based measures (amplitude spectra), and parameterized feedback modeling. We found that posture differed in both magnitude and frequency distribution during sway referencing compared with quiet sitting. Modeling indicated that sway referencing caused greater uncertainty/noise in sensory feedback and motor outputs. Sway referencing was also associated with lower active stiffness and damping model parameters. The influence of vision and a cognitive task was more apparent during sway referencing compared with quiet sitting. Short-term learning was reflected by reduced RMS velocity in quiet sitting immediately following sway referencing. Longer term learning was evident from one week to the next, with a 23% decrease in RMS sway and 9% decrease in RMS velocity. These changes occurred predominantly during cognitive tests at lower frequencies and were associated with lower sensory noise and higher stiffness and integral gains in the model. With the findings taken together, the sitting sway-referenced test elicited neural changes consistent with optimal integration and sensory reweighting, similar to standing, and should be a valuable tool to closely examine sensorimotor control of the trunk. NEW & NOTEWORTHY We developed the first sway-referenced system for sitting to highlight the role of vestibular and visual contributions to trunk control. A parametric feedback model explained sensorimotor control and motor learning in the task with and between two test sessions. The sitting sway-referenced test elicited neural changes consistent with optimal integration and sensory reweighting, similar to standing, and should be a valuable tool to closely examine sensorimotor control of the trunk.

A Novel Trunk Rehabilitation Robot Based Evaluation of Seated Balance Under Varying Seat Surface and Visual Conditions

“…We have developed a novel trunk rehabilitation robot [19,20] that can generate seat motion in multiple degrees of freedom and has a footrest structure that is connected rigidly to the seat in order to limit fully the proprioceptive feedback from the LE so that the sensory and control duties all have to be performed by the trunk [18]. In the presented study, we have used this robot to evaluate the effects of different seat modes and visual modes on the various COP and trunk movement parameters derived from data recorded during the performance of a simple upright balance maintenance task under different trial conditions.…”

“…In order to eliminate fully the proprioceptive feedback from the LE so that the sitting postural control duties have to be performed by the trunk, the LE must be constrained to move with the pelvis so that there is no movement of the joints as the pelvis is rotated [18]. Keeping this in view, we have recently developed a novel trunk rehabilitation robot that has the ability to generate seat motion in multiple degrees of freedom and has a footrest structure that is connected rigidly to the seat so that the feet have no motion relative to the pelvis [19,20].…”

Human manual control precision depends on vestibular sensory precision and gravitational magnitude

“…Emphasizing the relationship between our measurements, we calculated PVM as the standard deviation of manual control system response, and, similarly, thresholds reflect the standard deviation of sensory noise. These noise measures are also equivalent to those used in stochastic models of dynamic spatial orientation (Borah et al 1988;Karmali et al 2018;Karmali and Merfeld 2012;Laurens and Angelaki 2017;Lim et al 2017) and postural control (Assländer and Peterka 2016;Goodworth et al 2018;van der Kooij et al 1999van der Kooij et al , 2001van der Kooij and Peterka 2011), and future work could extend these models to stochastic closed-loop manual control tasks. Demonstrating the broader utility of precision measures, we also note that roll-tilt and linear translation vestibular perceptual thresholds have been shown to be sensitive to disorders such as vestibular migraine and Ménière's disease (Bremova et al 2016;Lewis et al 2011).…”

“…Manual control and postural control are similar in that both use closed-loop feedback control and are approximated by a single-link inverted pendulum (Panic et al 2015;Riccio et al 1992). Modeling of postural responses to perturbations with closed-loop models suggests that postural variability and sway arise from imprecision in vestibular sensation, vision, proprioception, and muscle control (Goodworth et al 2018;Mergner et al 2005;Peterka 2002;van der Kooij et al 1999van der Kooij et al , 2001van der Kooij and Peterka 2011). Furthermore, age and vestibular roll-tilt 0.2 Hz thresholds are both correlated (using a multiple variable logistic regression) with pass/fail performance in a balance test in which subjects are asked to stand on foam with eyes closed (Bermúdez Rey et al 2016;Karmali et al 2017).…”

The Influence of Different Levels of Cognitive Engagement on the Seated Postural Sway

“…Similarly, while seated, the human body is subject to a number of disturbances and, also in this condition, the CNS modulates the activity of muscles to maintain the equilibrium of the upper body segments (e.g., upper trunk, head, upper limbs) [27]. Correspondingly, in a seated position it is possible to determine where the Upper body Center of Pressure (UCOP) is located over a period of time, in order to evaluate, for example, if, in the presence of different external stimuli, or during task execution, a different way of swinging can be identified and to what it can be associated.…”