Strategies for targeting deep brain structures using the TES reciprocity based methods

PHAN LUU; MARIANO FERNÁNDEZ CORAZZA; CARLOS MURAVCHIK; SERGEI TUROVETS; DON TUCKER

Barcelona

Conferencia; 2nd International Brain Stimulation Conference; 2017

Elsevier, Inc.

Introduction: Targeting thedeep brain structures in transcranial electrical stimulation (TES) is difficultdue to a diffuse nature of the volume conduction and complex geometrical andelectrical properties of the head. We propose and analyse two independentstrategies: 1) to include a few minimally invasive electrodes into the nasal cavity,and 2) to rotate the targeting orientation over time to lower the currentexposure of the non-target regions (dynamic targeting).Methods: A detailed eight-tissueand 6 million finite element (FE) head model was built from subject specificMRI, CT and DTI, including 128 or 256 electrodes, skull holes, marrow bone,eyeballs, internal air pockets, and anisotropy of the grey and white mattertissues. The TES reciprocity methods are based on projecting the electroencephalography(EEG) lead field to the scalp from dipoles placed at the ROI oriented along thedesired targeting direction, and selecting the source and sink electrodeclusters around the poles of the resulting EEG topography [1].Results: We selected fourdeep targets of interest located in the insula, Brodman area 48, theparahypocammpal gyrus, and the anterior cingulate cortex. For each target we obtainedthe current injection and cortical stimulation patterns by reciprocity using: i)scalp electrodes; ii) scalp and nasopharyngeal electrodes, and iii) dynamictargeting.Discussion: We found that,depending on the target, its orientation, and the assumed safety constraints,the addition of extra electrodes into the nasopharyngeal cavity can double thecurrent densities at the deep targets. In dynamic targeting with five differentorientations, the maximum current density at non-ROI brain regions is reducedapproximately by 30% while the energy delivered to the ROI is reduced only by10% effectively increasing the ROI to non-ROI maximum exposure ratio.References:[1] Fernandez-Corazza, M., et al. Front Psychiatry, 2016.doi:10.3389/fpsyt.2016.00087.