Unpacking Galvanic Vestibular Stimulation using simulations and relating current flow to reported motions: Comparison across common and specialized electrode placements

Galvanic Vestibular Stimulation is a non-invasive electrical stimulation technique that is typically used to probe the vestibular system. While commonly delivered using two electrodes, additional electrode placements have been employed. Our objective was to systematically evaluate all known placements, compare induced current flow, and how it relates to the archetypal virtual and sway motions. The ultimate goal is to help users in having a better understanding of the effects of different configurations. We simulated seven placements using an ultra-high-resolution model. Induced electric field (EF) patterns at the cortical and the location of vestibular organs were determined. As expected, current flow patterns are electrode placement specific. Placements with two electrodes generally result in higher EF magnitude. Placements with four electrodes result in lower percentage of current entering the cranial cavity. Symmetric placements do not result in similar EF values in the left and the right organs highlighting inherent anatomical asymmetry. Asymmetric placements may result in as much as ~ 3-fold higher EF in one organ over the other. The percentage of current entering the cranial cavity varies between ~ 15–40% depending on the placement. Detailed analysis such as this may be used to help understand mechanism of action, guide stimulation strategy, ultimately resulting in quantitatively informed rational / optimal choices.