Simulation of Cortical Electric Fields during Deep Brain Simulation (DBS)

Background : Deep Brain Stimulation (DBS) is an established treatment for patients with neurological and psychiatric conditions. Traditionally, DBS has focused on the strong electric fields generated near the electrode site in subcortical regions. However, weak electric fields, which are less intense and extend further away from the stimulation site into cortical regions, are also present and may influence treatment outcomes. Noninvasive brain stimulation techniques, such as transcranial current stimulation (tCS), have shown that these weak fields can modulate brain activity effectively, suggesting that the weak fields generated during DBS could also play a significant role in treatment outcomes. The DESYNCHRONIZING WEAK CORTICAL FIELDS DURING DEEP BRAIN STIMULATION (DECODE) project investigates the impact of these weak fields on neural activity during DBS. This study, part of the DECODE project, aims to develop a general head model for DBS simulations to quantify and compare the electric field magnitude and distribution in cortical regions. Objective : To quantify and investigate the strength and spatial distribution of electric fields in the cortical regions for monopolar and bipolar configurations during deep brain stimulation when using the Medtronic 3389 lead implanted in the subthalamic nucleus (STN). Methods : The electric field distribution was calculated using a numerical method with a realistic head model, incorporating Medtronic 3389 DBS leads. Multiple toolboxes were used to gather data for the model creation. Mesh generation was performed with Iso2Mesh, and cortical parcellations were obtained from FreeSurfer. The simulations were carried out using FEMfuns with an input current of 2 mA. The electric field and parcellation data were subsequently post-processed to obtain an electric field for cortical regions. Results : Monopolar simulations generate electric fields with mean magnitudes ranging from 0.0154 V/m to 0.2556 V/m and maximum values up to 3.13 V/m, with contact 3 showing the highest mean magnitude of the electric field, ranging from 0.0173 V/m to 0.2556 V/m and maximum values up to 3.13 V/m. In bipolar simulations, the mean magnitude of the electric field varies between 0.001 V/m and 0.12 V/m, with maximum values up to 1.94 V/m. Within bipolar configurations, simulations 2 and 4 show the highest mean magnitude of the electric field, with values ranging from 0.001 V/m to 0.12 V/m, and maximum electric field values up to 1.9373 V/m. Conclusion : Monopolar configurations influence more cortical regions, while bipolar con-figurations offer more targeted stimulation within the cortical regions. The findings show that monopolar configurations, particularly with contact 3, generate stronger and more widespread electric fields than bipolar configurations, which produce more localized fields. The results highlight that varying contact positions significantly influence the electric field’s magnitude and distribution, with contact 3 in monopolar configuration and specific cathode-anode pairings in bipolar setups offering optimal stimulation conditions. Notably, the mean magnitudes of electric fields generated within the cortical regions by both monopolar and bipolar DBS configurations are within the same order of magnitude as those produced by other noninvasive brain stimu-lation techniques. However, the maximum electric fields within the cortical regions generated by DBS are one order of magnitude, or slightly more, higher than the maximum electric fields produced by tCS.