Background on methods of stimulation in galvanic-induced body sway in young healthy adults.

The aim of this study was to develop a standardized procedure for reproducible quantification of galvanic-induced body sway (GBS). This was a prospective experimental study conducted in a tertiary referral centre. An exploratory study was first conducted to define the galvanic vestibular stimulation (GVS) method that resulted in the best reproducible responses. Ten subjects underwent computer-controlled GVS using five different types of monaural and binaural stimulation with 2-mA currents. Cosinusoidal stimulation gave the most reproducible responses. The frequency and current variability of this stimulus type were then tested in the same 10 subjects. A monaural continuous 1-cosinusoidal current of 0.5 Hz and 2 mA gave the most reproducible responses (< 20% test-retest variation) and the largest GBS amplitude. The other (sinusoidal) stimuli resulted in variabilities exceeding 50%. This stimulus was thus used for further testing in our normative study. In this study we measured GBS amplitude at 0.5 Hz in 60 subjects, with eyes closed and an inter-feet distance of 0 cm, using a force platform. In addition to body sway, responses included slight dizziness, taste sensations and a tingling sensation at the site of stimulation. Habituation to the applied stimulus was seen. Binaural prestimulation, performed in 50/60 test subjects, is necessary to reduce habituation and achieve optimal reproducibility in order to be able to compare the sensitivity of the left and right vestibular systems. The test-retest variability was determined in detail in 12 additional subjects. Prestimulation reduced habituation, but improved the sensitivity of the method; some test-retest variability persisted (< 20%).