Response of Vestibular Afferents to Transcutaneous Electric Stimulation: Comparison with Response to Perilymphatic Electric Stimulation

Park, Hong Ju

Abstract

BACKGROUND AND OBJECTIVES
TElectrical stimulation has been used for several vestibular tests, such as galvanic body sway tests and galvanic evoked myogenic responses. In these tests, small amplitude galvanic currents are delivered transcuta-neously to the vestibular afferents. It is noted, however, there has not been any reports concerning the difference between the afferent-responses to transcutaneous and perilymphatic galvanic stimulations. SUBJECTS AND METHOD: We used anesthetized chinchillas and made extracellular recordings from vestibular afferents. Galvanic currents were applied transcutaneously and perilymphatically, and we compared the responses of vestibular afferents at each condition. RESULTS: Irregular afferents had characteristically large galvanic responses and regular afferents had characteristically small responses. For regularly discharging afferents, the mean galvanic sensitivities to anodal/cathodal currents were 0.22+/-0.23/0.23+/-0.17 spikes.s-1/microA (n=17), and 1.64+/-2.18/1.88+/-2.07 spikes.s-1/microA for irregularly discharging afferents (n=11). The estimated amplitude of perilymphatic galvanic stimulus, which showed the same changes of the resting rates by transcutaneous galvanic stimulation using 1 mA, were 65.0/66.0 microA for regularly and irregularly discharging afferents, respectively. CONCLUSION: These findings suggest that transcutaneous galvanic stimulation affects irregular afferents more than regular afferents perilymphatic galvanic stimulation. And more than 1.54 mA amplitude of transcutaneous galvanic stimulation is needed to ablate irregularly discharging afferents functionally.