Ex vivo studies of efficacy of DeepFocus: a technique for minimally-invasive deep-brain stimulation

Invasive deep-brain stimulation is increasingly being investigated as a treatment for neural disorders. A non-invasive alternative for deep-brain neuromodulation would likely broaden the range of application. However, existing techniques, such as transcranial electrical or magnetic stimulation (TES, TMS), are limited in their depth of stimulation. In this work, we propose DeepFocus, a new minimally invasive approach for stimulation of the deep brain by inserting electrodes in nasal cavities in conjunction with conventional scalp electrodes. As an initial step, an ex vivo model was designed to quantify the current efficiency of the proposed electrode placement in eliciting neural responses. A simplified geometric configuration was employed, where two linear electrode arrays arranged perpendicularly were used to elicit local field potentials (LFP) in mouse brain slices. Through a combination of finite element simulations to model the electric fields, and LFP measurements, we observed that electrode-patterns that use both arrays (modeling transnasal and scalp electrodes) generated higher electric fields and required less current to evoke responses compared to those that use only a single array (modeling scalp-only or transnasal-only). The benefits of two-array stimulation increased as the distance between the electrodes and the brain slice was increased. In addition, we observed that the relative orientation of the electric field compared to the cortical columns affected the neural responses.