Department of Biomedical Engineering, Duke University, Durham, NC, USA.
J Neural Eng. 2010 Dec;7(6):066009. doi: 10.1088/1741-2560/7/6/066009. Epub 2010 Nov 17.
Deep brain stimulation (DBS) has emerged as an effective treatment for movement disorders; however, the fundamental mechanisms by which DBS works are not well understood. Computational models of DBS can provide insights into these fundamental mechanisms and typically require two steps: calculation of the electrical potentials generated by DBS and, subsequently, determination of the effects of the extracellular potentials on neurons. The objective of this study was to assess the validity of using a point source electrode to approximate the DBS electrode when calculating the thresholds and spatial distribution of activation of a surrounding population of model neurons in response to monopolar DBS. Extracellular potentials in a homogenous isotropic volume conductor were calculated using either a point current source or a geometrically accurate finite element model of the Medtronic DBS 3389 lead. These extracellular potentials were coupled to populations of model axons, and thresholds and spatial distributions were determined for different electrode geometries and axon orientations. Median threshold differences between DBS and point source electrodes for individual axons varied between -20.5% and 9.5% across all orientations, monopolar polarities and electrode geometries utilizing the DBS 3389 electrode. Differences in the percentage of axons activated at a given amplitude by the point source electrode and the DBS electrode were between -9.0% and 12.6% across all monopolar configurations tested. The differences in activation between the DBS and point source electrodes occurred primarily in regions close to conductor-insulator interfaces and around the insulating tip of the DBS electrode. The robustness of the point source approximation in modeling several special cases--tissue anisotropy, a long active electrode and bipolar stimulation--was also examined. Under the conditions considered, the point source was shown to be a valid approximation for predicting excitation of populations of neurons in response to DBS.
深部脑刺激（DBS）已成为治疗运动障碍的有效方法；然而，DBS 发挥作用的基本机制尚不清楚。DBS 的计算模型可以深入了解这些基本机制，通常需要两步：计算 DBS 产生的电潜力，然后确定细胞外电势对神经元的影响。本研究的目的是评估在计算模型神经元周围群体对单极 DBS 的反应的激活阈值和空间分布时，使用点源电极近似 DBS 电极的有效性。使用点电流源或 Medtronic DBS 3389 导联的几何精确有限元模型计算各向同性均匀容积导体中的细胞外电势。将这些细胞外电势与模型轴突群体耦合，并确定不同电极几何形状和轴突方向的阈值和空间分布。对于所有取向、单极极性和电极几何形状，单个轴突的 DBS 和点源电极之间的阈值差异中位数在 -20.5%和 9.5%之间变化。对于给定幅度，点源电极和 DBS 电极激活的轴突百分比差异在所有测试的单极配置中在 -9.0%和 12.6%之间变化。DBS 和点源电极之间的激活差异主要发生在导体-绝缘体界面附近和 DBS 电极的绝缘尖端周围。还检查了点源近似在模拟几种特殊情况（组织各向异性、长有源电极和双极刺激）中的稳健性。在所考虑的条件下，点源被证明是一种有效的近似方法，可用于预测 DBS 对神经元群体的兴奋。
