Abstract
Human multimodal vestibular cortical regions are bilaterally anterior insulae and posterior opercula, where characteristic vestibular-related cortical potentials were previously reported under acoustic otolith stimulation. Galvanic vestibular stimulation likely influences semicircular canals preferentially. Galvanic stimulation was compared to previously established data under acoustic stimulation. 14 healthy right-handed subjects, who were also included in the previous acoustic potential study, showed normal acoustic and galvanic vestibular-evoked myogenic potentials. They received 2,000 galvanic binaural bipolar stimuli for each side during EEG recording. Vestibular cortical potentials were found in all 14 subjects and in the pooled data of all subjects ("grand average") bilaterally. Anterior insula and posterior operculum were activated exclusively under galvanic stimulation at 25, 35, 50, and 80 ms; frontal regions at 30 and 45 ms. Potentials at 70 ms in frontal regions and at 110 ms at all of the involved regions could also be recorded; these events were also found using acoustic stimulation in our previous study. Galvanic semicircular canal stimulation evokes specific potentials in addition to those also found with acoustic otolith stimulation in identically located regions of the vestibular cortex. Vestibular cortical regions activate differently by galvanic and acoustic input at the peripheral sensory level. Differential effects in vestibular cortical-evoked potentials may see clinical use in specific vertigo disorders.
Highlights
Human multimodal vestibular cortical regions are bilaterally anterior insulae and posterior opercula, where characteristic vestibular-related cortical potentials were previously reported under acoustic otolith stimulation
Galvanic semicircular canal stimulation evokes specific potentials in addition to those found with acoustic otolith stimulation in identically located regions of the vestibular cortex
– Multimodal vestibular network 3-D EEG dipoles mapped with Brain-Evoked Source Analysis (BESA). – Specific evoked cortical potentials 25–110 ms. – Different potentials in semicircular versus known otolith potentials
Summary
Human multimodal vestibular cortical regions are bilaterally anterior insulae and posterior opercula, where characteristic vestibular-related cortical potentials were previously reported under acoustic otolith stimulation. The current study investigates the same time range beyond 20 ms with a different, galvanic vestibular stimulus directed preferentially at the semicircular canal organs [9] rather than the previously used otolith-focused specific acoustic stimulation [(8) and references therein]. Galvanic vestibular stimulation (GVS) is the application of such currents over the mastoid bones, either bilaterally with oppositely polarized electrodes (“bipolar”) or monopolar (cathodal or anodal) against a reference positioned mostly over the C7 vertebra. Effects of GVS on saccular and utricular fibers (preferentially excited by acoustic vestibular stimulation) are considered negligible [26] and can only be isolated during very specific paradigms like simultaneous specific physical rotation of the body [9]. Depending on the duration of GVS stimuli, physiological responses can be vestibular perceptions, eye movements, and/or postural reactions [11, 26,27,28,29]
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