Analysis of postural control adaptation during galvanic and vibratory stimulation

The objective for this study was to investigate whether the postural control adaptation during galvanic stimulation of the vestibular nerve were similar to that found during vibration stimulation to the calf muscles. A method for adaptation analysis was used to analyze the evoked changes of posture, stimulus responses and the motion dynamics. The adaptive adjustments of postural control were similar during galvanic and vibratory stimulation, which suggests that the adaptation operate in the same way independent of the receptor systems affected by the disturbance. There was however a difference in the dynamic feedback properties of the measured responses. Introduction If a repeated disturbance of postural control becomes more intense, it usually initiates an adaptive process to improve the control performance (1-3). However, it is unknown whether this adaptive process is similar independently on receptor system affected by the disturbance. The adaptive adjustments were therefore analyzed during posturography with perturbations induced by disturbances of vestibular and proprioceptive information. The adaptive adjustments in postural control were quantified by a method approach describing postural control as a dynamic feedback control. The method provides a mathematical model of the relationship between induced disturbances and counteractive body sway responses (4). The aim of this study was to investigate if the adaptive processes and motion response dynamics were similar whether perturbed by galvanic or vibratory stimulation. Methods Galvanic stimulation of the vestibular nerve was performed on 12 test subjects (6 men, 6 women; mean age 41 years, range 23-56 years). Vibratory stimulation was performed on 10 healthy subjects (6 men, 4 women; mean age 37.5 years, range 29-56 years). The galvanic vestibular stimulation was applied as bipolar and binaural square pulses of 1 mA amplitude with pseudorandomly shifting polarity. The pulses were delivered by a constant current generator through two electrodes placed on each of the mastoids. Vibratory stimulation was applied to the gastrocnemius muscles of both legs. The vibratory amplitude was 1.0-mm and the frequency 85 Hz. Forces and torques actuated by the feet were recorded by a force platform and data were sampled at 10 Hz. The subjects were told to stand erect but relaxed and feet at an angle of about 30 degrees. Spontaneous sway was recorded for 30 seconds of quiet stance, after which the vibrators for 200 seconds were turned on and off according to a pseudorandom binary sequence (PRBS) containing pulses varied between 0.8 to 6.4 seconds. The experiments were conducted both with eyes closed and open. Analysis The measured lateral torque during galvanic stimulation and anteroposterior torque during vibratory stimulation was analyzed with a method considering the adaptation of postural control. The method aims to describe the adaptation of the slow posture motion as well as the adjustments of the stimulation responses. This information is used to estimate a time-invariant Report Documentation Page Report Date 25 Oct 2001 Report Type N/A Dates Covered (from... to) Title and Subtitle Analysis of Postural Control Adaptation During Galvanic and Vibratory Stimulation Contract Number Grant Number Program Element Number Author(s) Project Number Task Number Work Unit Number Performing Organization Name(s) and Address(es) Department of Otorhinolaryngology University Hospital of Lund Lund, Sweden Performing Organization Report Number Sponsoring/Monitoring Agency Name(s) and Address(es) US Army Research, Development & Standardization Group (UK) PSC 802 Box 15 FPO AE 09499-1500 Sponsor/Monitor’s Acronym(s) Sponsor/Monitor’s Report Number(s) Distribution/Availability Statement Approved for public release, distribution unlimited Supplementary Notes Papers from 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society, October 25-28, 2001, held in Istanbul, Turkey. See also ADM001351 for entire conference on cd-rom., The original document contains color images.