Abstracts

Rationale: We have successfully used tripolar concentric ring electrodes (TCREs) to apply transcranial focal electrical stimulation (TFS) in multiple animal models of epilepsy (Santana-Gomez et al. 2015). To translate our positive animal model results to humans, we have developed a four concentric spheres computer human head model. The model will allow us to understand the requirements needed to modulate human brain noninvasively. We used Comsol Multiphysics, a finite element simulation software, to create and simulate a human head. We developed a model with 1 V/m electric fields in the cortex since (Vöröslakos et al. 2018) determined in vivo 1 V/m was strong enough to activate neurons.

Methods: A four concentric spheres (scalp, 184mm dia., skull, 170mm dia., CSF, 160mm dia., and brain, 154mm dia.) finite element model was constructed. The electrical conductivity material properties were assigned to each geometry used in the model (scalp 0.44 S/m, skull 0.018 S/m, CSF 1.75 S/m, and brain 0.25 S/m). Relative permeabilities of all materials were set to 1. The outer ring diameters were 15mm and 16mm. The center disc had a diameter of 2.8mm. The impedance matching paste had an electrical conductivity of 0.44 S/m and was modelled as an 18mm dia. and 2mm thick disc. The electric fields were calculated due to 0.05 A current applied between the outer ring and central disc of the TCRE.

Results: In our previous work, we used 10mm dia. on the outer ring of the electrode. The simulations showed that we could not reach 1 V/m using 0.05 A with a 10mm dia. TCRE. We had to increase the diameter of the outer ring of the TCRE as well as the diameter of the paste, described above, to achieve 1 V/m electric fields without surpassing the preferred limit of 0.05 A.

References:
César E. Santana-Gómez, David Alcántara-González, Hiram Luna-Mungia, Ivette Bañuelos-Cabrera, Víctor Magdaleno-Madrigal, Walter Besio, Luisa Rocha “Transcranial focal electrical stimulation reduces the convulsive expression and amino acid release in the hippocampus during pilocarpine-induced status epilepticus in rats“, Epilepsy & Behavior, 2015

Vöröslakos, M., Takeuchi, Y., Brinyiczki, K., Zombori, T., Oliva, A., Fernández-Ruiz, A., … Berényi, A. (2018). Direct effects of transcranial electric stimulation on brain circuits in rats and humans. Nature Communications, 9(1). https://doi.org/10.1038/s41467-018-02928-3

Conclusions: Our four concentric spheres human head model shows us that we should be able to modulate human brain by reaching 1 V/m using 0.05 A and a 16mm dia. TCRE.

Funding: Please list any funding that was received in support of this abstract.: NSF award #1701049.