Temporal Interference Transcranial Electrical Stimulation in Humans: Actual Doses and Steerability

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

Nueva York

Conferencia; 2018 NYC Neuromodulation Conference and NANS Summer Series; 2018

North American Neuromodulation Society (NANS)

Temporal Interference TranscranialElectrical Stimulation in humans: actual doses and steerability   Mariano Fernández-Corazza1,2,Sergei Turovets2,3, Phan Luu3, Don Tucker2,3.  1LEICI Instituto deInvestigaciones en Electrónica, Control y Procesamiento de Señales, UniversidadNacional de La Plata - CONICET, Argentina,  2NeuroInformatics Center,University of Oregon, Eugene, OR, USA,  3Philips Neuro Diagnostics,Eugene, OR, USA Following the paperby Grossman et al [GrossmanN.  et al.   Noninvasive deep brain stimulation viatemporally interfering electric fields. Cell . 2017;169(6):1029-1041. ] there has been arenewal of   interest to temporalinterference (TI) transcranialelectrical stimulation (TES)  introduced  clinically in the 1960s in context of electrosleep. InTI, two relatively high frequency signals are injected transcranially, and thebrain (normally non-responsive to each of the signals separately) rectifies thedifferential low frequency beat (beating?) signal and gets stimulated. It wasproven in a mouse model and phantoms, that such stimulation is spatiallyselective and steerable by manipulating the amplitude and location of fronto-occipitalelectrode pairs. In our present study, we have performed extensive FEM simulations of TI TES within anatomically accuratehuman head geometry to document attenuation effects of the real human skull andexplore actual steerability of stimulation spots. We have confirmed the presence of the localcurrent density maxima of the beating signal inside of the deep human brain structures such as the corpuscallosum, brain stem and thalamus. It is typically 1-1.5 times the currentdensity maxima in the nearby overlying cortex, flabby or focal depending on theinjection points, and, due to the human skull attenuation, significantly weaker(around 30 times) than the beat signal maximum on the scalp. The directionof the beat current density rotates in time with the same differentialfrequency of the original stimulation alternative (alternating?) currents, reducinga directional dose. We plotted snapshots of the 3D maps of the maximum stimulating currents and found its directionality is spatiallydependent. To overcome attenuating impact of the skull, we have simulateda use of i) minimally invasive subgaleal electrodes and ii) natural skullopening. The second was facilitated by placing stimulating electrodesnon-invasively near the eyelids (which is harmless and causes no phosphines ifthe stimulating frequencies are high) and paired electrodes near the bottom ofthe neck (close to the big foramina) or the ears. We have also testedsteerability of the maximum stimulation spot inside the brain  by varying the relative amplitude of the twoinjected signals and positions of the rear electrodes by moving them graduallyfrom the neck to the ears and demonstrated shifts of the hot stimulation spotfrom left to right and from posterior to anterior.