Abstract WP139: Transcranial Direct Current Stimulation (tDCS) Generates Electric Fields (EF) at the Level of Deep Nuclei of the Human Brain in vivo

Abstract

Introduction: tDCS is an investigational neuromodulatory therapy for stroke recovery and data has been inconsistent and mixed. The general perception for tDCS is that the majority of current gets shunted at the level of scalp and only minor portion penetrates to the superficial cortex. We aimed to detect electrical field (EF) via deep brain stimulation (DBS) leads in human brain. Hypothesis: Scalp-applied tDCS generates EF across the brain and forms detectable voltage gradient across DBS leads. Methods: We recruited patients undergoing DBS stage 2 procedure (implantable pulse generator or IPG implantation). We connected our recording setup to the IPG end of the DBS lead(s), which is otherwise unavailable except this specific surgical procedure. We applied 2 mA and 4 mA of tDCS using bitemporal and occipitofrontal montage and recorded voltage gradients across electrodes of DBS lead(s), while monitoring the applied voltage, injected current and body resistance through tDCS setup. Results: We recruited 3 patients with unilateral or bilateral DBS leads and found that tDCS application results in changed voltage gradient across contact points of the leads. Because of side-by-side orientation of the leads, bitemporal montage induces in voltage gradient in dose-dependent manner, but occipitofrontal montage did not detect any voltage gradient across the DBS leads because of their relatively equidistant positioning from the anode/cathode. Finally, 4 mA of tDCS resulted in lower body resistance (~20-30% less) when compared to 2 mA of tDCS. Conclusions: tDCS-generated EF were detected at the level of deep nuclei. Our findings offer insights into the body’s changing resistance to tDCS in a dose-dependent manner that can optimize tDCS simulation models towards improving tDCS efficacy in stroke recovery.