Proceedings #21. Intracranial Voltage Recording during Transcranial Direct Current Stimulation (tdcs) in Human Subjects with Validation of a Standard Model

s / Brain Stimulation 10 (2017) e46ee83 e72 [19] Trevizol 2016 Trigeminal nerve stimulation (TNS) for posttraumatic stress disorder and major depressive disorder: An open-label proof-ofconcept trial [20] Fallgatter 2003 Far field potentials from the brain stem after transcutaneous vagus nerve stimulation. [21] Stavrakis 2015 Low-level transcutaneous electrical vagus nerve stimulation suppresses atrial fibrillation. [22] Fang 2015 Transcutaneous Vagus Nerve Stimulation Modulates Default Mode Network in Major Depressive Disorder. [23] Rong 2016 Effect of transcutaneous auricular vagus nerve stimulation on major depressive disordera nonrandomized controlled pilot study [24] Huston 2007 Transcutaneous vagus nerve stimulation reduces serum high mobility group box 1 levels and improves survival in murine sepsis [25] _Ellrich 2011 Inhibition Of Pain Processing By Transcutaneous Vagus Nerve Stimulation (Abstract & Poster) [26] Ellrich 2011 Analgesic Effects of Transcutaneous Vagus Nerve Stimulation (Abstract) [27] Nitsche & Paulus 2000 Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation [28] Bikson 2016 Safety of Transcranial Direct Current StimulationEvidence Based Update 2016 PROCEEDINGS #21. INTRACRANIAL VOLTAGE RECORDING DURING TRANSCRANIAL DIRECT CURRENT STIMULATION (TDCS) IN HUMAN SUBJECTS WITH VALIDATION OF A STANDARD MODEL Zeinab Esmaeilpour , Matija Milosevic , Kleber Azevedo , Niranjan Khadka , Jessie Navarro , Andre Brunoni , Milos R. Popovic , Marom Bikson , Erich Talamoni Fonoff . Department of Biomedical Engineering, the City Collage of New York, NY, USA; 2 Institute of Biomaterials and Biomedical Engineering, University of Toronto, ON, Canada; Rehabilitation Engineering Laboratory, Toronto Rehabilitation Institute University Health Network, Toronto, ON, Canada; Division of Functional Neurosurgery of Institute of Psychiatry of Hospital das Clinicas of University of S~ ao Paulo medical School, Brazil; 5 Institute of Psychiatry of Hospital das Clinicas of University of S~ ao Paulo medical School, Brazil; Department of Neurology and Division of Functional Neurosurgery of Institute of Psychiatry of Hospital das Clinicas of University of S~ ao Paulo medical School, Brazil 1. Abstract and Introduction During transcranial direct current stimulation (tDCS) weak (1-2 mA) currents are applied across the head, producing low-intensity electric fields in the brain with the intention of modulating neuronal function. For any application of tDCS spanning cognitive neuroscience and neuropsychiatric therapies [1], understanding the amount of current delivered to the brain and the resulting electric field (in V/m) produced is thus important. In animal studies, direct current (DC) electric fields as low as 0.2-1.0 V/m influence neuronal excitability and plasticity [2, 3]. Since measurement of electric field in human is difficult to implement, high-resolution finite element head models [4] have been used to predict brain current flow during tDCS [5] with many reports adapting a standard (S#) head [6-8]. There have been previous attempts to validate computational model predictions indirectly with scalp electrodes [9] and neurophysiology [10] during tDCS, as well as directly using intra-cranial electrodes, but not with DC stimulation [11, 12]. In this pilot study, DC voltage was measured using deep brain stimulation (DBS) and epidural lead electrodes during application of tDCS in human subjects. The results were evaluated against a standard (S#) head model. The model predictions of voltage produced across cortical (epidural) electrodes were consistent with recorded data, while subcortical (DBS) voltages were sensitive to conductivity assigned to subcortical structures. 2. Methods Three subjects were recruited for the study: subject #1 59 years old male, two DBS electrodes implanted bilaterally (3387, Medtronic Inc., USA) in nucleus accumbens (NA), subject #2 51 years old male, two DBS electrodes implanted bilaterally (6145, St. Jude Medical Inc., USA) in subthalamic nucleus (STN), subject #3 32 years old male, two epidural electrode strips implanted unilaterally (3240, St. Jude Medical Inc., USA) over the right motor cortex. Each electrode contained four recording points separated by 1.5mm (DBS) and 10mm (epidural), resulting in 8 channels. All subjects signed a written consent form and experimental protocol was approved by Ethics committee of Institute of Psychiatry of Hospital das Clinicas of University of S~ ao Paulo with the code 0636/09. All subjects were stimulated with tDCS using O2supraorbital (EEG 10-20) montage, 5x7 cm electrodes for ~30 seconds with current ranging from 0-2 mA, in 1 mA increments. The voltage on each of the 8 electrodes in each subject was recorded during tDCS with reference to right earlobe at a sampling rate of 1200 Hz using a g.USBamp biosignal amplifier (g.tec, Austria). A standard head model (S#) was used to predict voltage distribution with aforementioned stimulation montage (Fig. 1). A standard set of electrical properties of tissue were assigned (in S/m): skin1⁄40.456, fat1⁄40.025, skull1⁄40.01, CSF1⁄41.65, grey matter1⁄40.276, whitematter1⁄40.126, air1⁄410 -̂15, electrode1⁄45.8*10 7̂ and gel1⁄41.4 [1, 5]. For modified conductivity, all parameters were fixed except for the grey matter1⁄40.207 S/m and white matter1⁄40.0945 S/m. Simulated voltages in locations corresponding to the center of each epidural electrode based on subject’s CT scan were used to evaluate cortical model predictions. In DBS modeling, averaged voltages in segmented subcortical nuclei (i.e. NA, STN) were used for model evaluation due to imprecise estimate of DBS electrode locations inside nuclei (i.e., no CT scan after surgery in DBS-implanted subjects).