Impact of galvanic vestibular stimulation electrode current density on brain current flow patterns: Does electrode size matter?

Abstract

Background Galvanic vestibular stimulation (GVS) uses at least one electrode placed on the mastoid process with one or multiple placed over other head areas to stimulate the vestibular system. The exact electrode size used is not given much importance in the literature and has not been reported in several studies. In a previous study, we compared the clinical effects of using different electrode sizes (3 cm2 and 35 cm2) with placebo but with the same injected current, on postural control. We observed significant improvement using the smaller size electrode but not with the bigger size electrode. The goal of this study was to simulate the current flow patterns with the intent to shed light and potentially explain the experimental outcome. Methods We used an ultra-high-resolution structural dataset and developed a model to simulate the application of different electrode sizes. We considered current flow in the brain and in the vestibular labyrinth. Results Our simulation results verified the focality increase using smaller electrodes that we postulated as the main reason for our clinical effect. The use of smaller size electrodes in combination with the montage employed also result in higher induced electric field (E-field) in the brain. Conclusions Electrode size and related current density is a critical parameter to characterize any GVS administration as the choice impacts the induced E-field. It is evident that the higher induced E-field likely contributed to the clinical outcome reported in our prior study.

Understanding the effect of pulse width on activation depth in TENS: A computational study

“…Computational modeling and simulation such as the one reported here is now increasingly used across a range of stimulation modalities, from optimizing delivery, performing safety analysis, to supporting device design / development [29,39 50-53]. Furthermore, these predictions have helped in elucidating stimulation parameter choices, understanding mechanism of action, explaining stimulation outcome, and thereby advancing stimulation administration in general [11, 54–57]. We expect this study on the arm to guide researchers in performing future explorations on other body parts, determine ideal pulse width range for target nerve of interest, attempt validation using TENS similar to the one performed in MS [23], and investigate new TENS delivery approaches.…”

Scoping out noisy galvanic vestibular stimulation: a review of the parameters used to improve postural control

“…The smaller sized electrodes, providing higher current density over a smaller area, resulted in a significant improvement in balance compared to the 35 cm 2 electrodes, that provided results that were no different to sham stimulation. Truong et al (2023) modeled the electrical effect of both 3, and 35cm 2 electrodes and reported the smaller electrode provided a more focal stimulation of the vestibular apparatus and temporal cortex, whereas there was more current loss via the skull and cerebrospinal fluid using a 35cm 2 electrode. To afford further support for the observation that smaller electrodes provide more specific, localized stimulation of the vestibular system, the size, shape and material of electrodes, and details around the electrode-skin interface, should be clearly reported.…”