A shared neural integrator for human posture control

Abstract

Control of standing posture requires fusion of multiple inputs including visual, vestibular, somatosensory, and other sensors, each having distinct dynamics. The semicircular canals, for example, have a unique high-pass filter response to angular velocity, quickly sensing a step change in head rotational velocity followed by a decay. To stabilize gaze direction despite this decay, the central nervous system supplies a neural "velocity storage" integrator, a filter that extends the angular velocity signal. Similar filtering might contribute temporal dynamics to posture control, as suggested by some state estimation models. However, such filtering has not been tested explicitly. We propose that posture control indeed entails a neural integrator for sensory inputs, and we test its behavior with classic sensory perturbations: a rotating optokinetic stimulus to the visual system and a galvanic vestibular stimulus to the vestibular system. A simple model illustrates how these two inputs and body tilt sensors might produce a postural tilt response in the frontal plane. The model integrates these signals through a direct weighted sum of inputs, with or without an indirect pathway containing a neural integrator. Comparison with experimental data from healthy adult subjects ( = 16) reveals that the direct weighting model alone is insufficient to explain resulting postural transients, as measured by lateral tilt of the trunk. In contrast, the neural integrator, shared by sensory signals, produces the dynamics of both optokinetic and galvanic vestibular responses. These results suggest that posture control may involve both direct and indirect pathways, which filter sensory signals and make them compatible for sensory fusion. Control of standing posture requires fusion of multiple inputs including visual, vestibular, somatosensory, and other sensors, each having distinct dynamics. We propose that postural control also entails a shared neural integrator. To test this theory, we perturbed standing subjects with classic sensory stimuli (optokinetic and galvanic vestibular stimulation) and found that our proposed shared filter reproduces the dynamics of subjects' postural responses.

Sensorimotor anatomy of gait, balance, and falls

“…The firing rate of semicircular canal afferents is approximately proportional to the angular velocity of the head and in phase with motion at frequencies above 0.1 Hz and up to 4.0 Hz (Fig. 1.5C) (Haggerty et al, 2017). The otolith organs have a similar system for sensing motion but have a structure specialized for encoding linear motion, in particular, sensing dynamic responses that are in phase with linear accelerations, including gravity.…”

“…The polysynaptic organization of the dorsal visual stream results in relatively slow reaction times to visual stimuli, in the order of 170 ms, or more and responses to optokinetic stimuli can take up to 10 seconds to reach steady state (Haggerty et al, 2017). Yet, if an object in the visual field unexpectedly moves, adjustments can be made from the planned trajectory of the upper or lower limb in the order of 120 ms (Patla et al, 1991;Day and Brown, 2001;Weerdesteyn et al, 2004;Reynolds and Day, 2005).…”

Modified Stabilization Test to Diagnose Chronic Syndesmotic Injuries Based on Posture Control

“…To eliminate visual interference during the eyes-open single-leg stand test, the line of sight fell on a red dot 65 cm from the test position (the height of the red dot was the same as the height of the line of sight). 15 Second, patients opened or closed their eyes on command. Each condition was repeated 3 times for 20 seconds.…”

Transiently Worse Postural Effects After Vestibulo-ocular Reflex Gain-Down Adaptation in Healthy Adults

“…Other studies have correlated measures of lateral semicircular canal VOR function with body sway, especially using an eyes closed on foam test to increase the postural demands on the vestibular system (Anson et al 2017(Anson et al , 2019. A recent paper described a model that accounts for separate signaling from semicircular canals (SCC) and otoliths to characterize postural control (Haggerty et al 2017), with the SCC effects described as detecting transients. Roll-tilt perception involving the otoliths and vertical SCC has been associated with postural control, but horizontal SCC perception was not (Karmali et al 2017;Beylergil et al 2019).…”