Postural Responses Evoked by Vibrational Stimulation of the Shin Muscles under Conditions of Virtual Visual Environment

Abstract

We studied the effects of unexpected shifts of the visually perceived artificial surroundings (virtual visual environment, VVE) on postural reactions evoked by vibrational stimulation of proprioceptors of the shin muscles; tests were performed in a standing position of the subject. The VVE possessed two planes, a mobile foreground, whose displacements correlated with oscillations of the body, and a stationary background. The subjects were asked to use the latter as a reference system in corrections of the posture. The VVE parameters were controlled by a computer; shifts of the VVE foreground were combined with similar, in their duration and profile, stimulation-evoked displacements of the body. Despite the fact that the subjects had a possibility to use the stationary background as the reference system, the magnitudes of the evoked postural responses under conditions of perception of the VVE significantly exceeded the respective magnitudes upon standing with the eyes open in front of a completely stationary visual image. Postural responses progressively increased with increases in relative values of the shifts of the VVE foreground but always remained smaller than the responses under conditions of testing with the eyes closed. Augmentation of the postural responses at a synphase pattern of interrelations between the body movements and VVE shifts was more significant than at antiphase relations. Thus, shifts of the VVE foreground, on the one hand, destabilized the maintenance of the vertical posture, which resulted in intensification of the postural responses. On the other hand, such shifts allowed the subject to use them as feedback signals and to modulate the magnitude of postural responses when there was a change in the direction of interrelations between the body movements and the perceived visual image.

A Short Duration Co-vibration Protocol of Antagonist Ankle Muscles to Induce Compensatory Postural Adjustments in Quiet Standing

“…The CoP oscillations consecutive to the short period of frequency change at 80 Hz were characteristics of previously reported postural responses to antagonist ankle muscles vibration: an anteroposterior displacement in the opposite direction of the vibrated muscle that drives the CoM in the direction of the vibrated muscle [5,7,[9][10][11][12]. The first CoP oscillation occurred with a latency shorter than 500 ms in both muscle groups, which seems reasonably close to what was observed previously [7,[10][11][12] although not reported. Initial CoP movement amplitude ( ) is found greater than in [10], indicating a greater sway to oppose the direction of the illusion.…”

“…Tendinous vibration of ankle muscles is a classical method used to alter kinesthetic sensory information and study postural control in humans [5,6]. When applied during quiet stance, two phenomena are observed: an illusion of swaying in the opposite direction of the vibrated muscle followed by CPA moving the body in the direction of the vibrated muscle [5][6][7][8][9][10][11][12]. However, vibrators classically used to alter kinesthetic information need time to reach the desired frequency.…”

Attenuation of the evoked responses with repeated exposure to proprioceptive disturbances is muscle specific

“…1-3, upper trunk (C7) and COP followed a similar trend in response to both calf and tibialis vibration indicating that participants largely adopted an ankle strategy (like inverted pendulums [23]). Therefore, as reported for C7, vibration induced COP displacements in the direction of the vibrated muscle which decreased with practice (p < .001 for velocity and peak amplitude).…”

Effects of Near-Threshold Stimulation of the Vestibular Apparatus on Postural Responses Evoked by Displacements of the Visualized Surrounding

“…As was shown, the direction of such response can change both upon real rotation of the head or creation of an illusion of its rotation [8,9]. Similarly to responses to galvanic stimulation, postural responses to stimulation of proprioceptors (e.g., to vibrational stimulation of the shin or neck muscles) also demonstrate noticeable dependence on the conditions of visual control [10,11].…”