Use of reciprocity in TES: ways of choosing the current injection electrodes.

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

Barcelona

Conferencia; 2nd International Brain Stimulation Conference; 2017

Elsevier, Inc.

Introduction: In transcranialelectrical stimulation (TES), it is important to maximize the current densityat a region of interest (ROI), and minimize it everywhere else. The TES reciprocitymethods are based on the computation of the electroencephalography (EEG) forwardproblem (FP), assuming dipoles at the brain ROI oriented along the desiredtargeting direction. We analyse the performance of different easy to implementand convenient ?ad-hoc? stimulating patterns based on the reciprocity principle,i.e., based on the scalp potential produced by the EEG dipoles.Methods: A detailedeight-tissue and 6 million finite element head model was built from subjectspecific structural MRI, CT and DTI, using the EGI modal image pipeline softwarefor segmentation and co-registration. It includes small skull holes, marrowbone, eyeballs, internal air pockets, 128 or 256 electrodes with conductivegel, and anisotropy of the grey and white matter tissues. Results: For fourrepresentative cortical shallow targets, we simulated the EEG FP, and defined fivecurrent injection patterns: one source-all sinks, one source-one sink, allelectrodes with injections proportional to EEG, equal current clusters at the EEGpoles, and proportional to EEG clusters. We assumed typical safety limits as atotal current injection of 1mA, and 0.1mA max. per electrode (except for thecases involving one electrode intentionally). Discussion: We found that,concentrating the current injection near the EEG poles instead of spreading itproportionally to the EEG pattern maximizes the current density at the target,as theoretically expected [1]. Injecting near the EEG poles should deliver thehigher densities to the ROIs in practical TES applications. The reciprocal useof measured EEG "without modelling" and the impacts of tissueconductivities are also discussed.References:[1] Fernandez-Corazza, M., et al. Front Psychiatry, 2016.doi:10.3389/fpsyt.2016.00087.