Virtual electrodes generated by focused penta-polar current stimulation for neuromodulation

Abstract

Virtual electrodes in neuromodulation can provide more delicate stimulation patterns with a limited number of physical electrodes in a confined area. Many researchers successfully verified the effectiveness of virtual electrodes in clinical trials, using current steering, which modulates electric fields produced by multi-polar stimulation. Still, it is questioned how these virtual electrodes are really generated in an electrolyte, especially in two dimensions. In order to answer this question, this work analyses the virtual electrode generation by comparing finite element analysis and in vitro evaluation of penta-polar stimulation. Penta-polar stimulation was realised using custom-designed integrated circuits and electrodes with an individual diameter of 450 μm and a centre-to-centre spacing of 800 μm. The customised test setup of electric field measurement estimated (i) the focused electric fields by the penta-polar stimulation and (ii) the optimum distance from the electrodes, at which virtual electrodes were most effectively generated. Compared with mono-polar stimulation, the penta-polar stimulation showed 0.594 and 0.545 times smaller electric field distribution areas, respectively, at a distance from the electrodes of 100 μm. Furthermore, the virtual electrodes showed the best performance at a distance from the electrodes of 150 μm, while the distance varied from 13 to 250 μm.