Cortical E-fields of deep brain stimulation in Parkinson's disease patients exceed typical E-field magnitudes of transcranial electrical stimulation

BackgroundDeep brain stimulation (DBS) is an established and effective intervention for Parkinsons disease. Although the exact mechanisms of action are still unclear, both therapeutic benefits and side effects are solely attributed to neuromodulation via strong electric fields (E-fields) in the surgical target. Nevertheless, DBS generates E-fields that extend beyond the stimulation site and can be detected throughout the brain. Recent evidence from transcranial electrical stimulation studies shows that weak cortical E-fields even below 1 V/m can have a neuromodulatory effect, raising the question of a physiological relevance of weak cortical fields of DBS. However, the strength of cortical E-fields of DBS is currently unknown. ObjectiveUsing a novel framework, we aimed to quantify the whole-brain E-field distribution in patients with Parkinsons disease receiving therapeutic DBS of the subthalamic nucleus (STN-DBS). MethodsIn this work, we developed a pipeline to simulate DBS E-field distributions throughout the brain, based on the existing open-source toolboxes Lead-DBS and SimNIBS. We constructed patient-specific whole-head models including electrode leads for 25 patients with Parkinsons disease receiving subthalamic DBS, and simulated E-fields using the patients clinical stimulation settings for 49 hemispheres. ResultsWe found that median peak E-field magnitudes exceeded 0.3 V/m in all cortical regions and were greater than 1 V/m in the orbital gyrus, superior temporal gyrus, fusiform gyrus, parahippocampal gyrus, insular gyrus, cingulate gyrus. Most prominently, the orbital and insular gyri showed peak magnitudes ranging from 0.81 to 8.61 V/m and 0.90 to 8.01 V/m. ConclusionsOur results indicate that the E-fields of STN-DBS reach cortical peak magnitudes that exceed typically reported values of transcranial electrical stimulation. This opens the possibility that weak E-fields of DBS could have a direct neuromodulatory effect in wider regions of the brain, for example in cortical regions.