McIntyre C C, Grill W M
Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106-4912, USA.
Ann Biomed Eng. 2001 Mar;29(3):227-35. doi: 10.1114/1.1352640.
Electrical stimulation via implanted microelectrodes permits excitation of small, highly localized populations of neurons, and allows access to features of neuronal organization that are not accessible with larger electrodes implanted on the surface of the brain or spinal cord. As a result there are a wide range of potential applications for the use of microelectrodes in neural engineering. However, little is known about the current-density and electric field generated by microelectrodes. The objectives of this project were to answer three fundamental questions regarding electrical stimulation with metal microelectrodes using geometrically and electrically accurate finite elements models. First, what is the spatial distribution of the current density over the surface of the electrode? Second, how do alterations in the electrode geometry effect neural excitation? Third, under what conditions can an electrode of finite size be modeled as a point source? Analysis of the models showed that the current density was concentrated at the tip of the microelectrode and at the electrode-insulation interface. Changing the surface area of the electrode, radius of curvature of the electrode tip, or applying a resistive coating to the electrode surface altered the current-density distribution on the surface of the electrode. Changes in the electrode geometry had little effect on neural excitation patterns, and modeling the electric field generated by sharply tipped microelectrodes using a theoretical point source was valid for distances > approximately 50 microm from the electrode tip. The results of this study suggest that a nearly uniform current-density distribution along the surface of the electrode can be achieved using a relatively large surface area electrode (500-1000 microm2), with a relatively blunt tip (3-6 microm radius of curvature), in combination with a thin (approximately 1 microm) moderately resistive coating (approximately 50 omega m).
通过植入式微电极进行电刺激能够激发少量高度局部化的神经元群体，并可获取通过植入大脑或脊髓表面的较大电极无法获得的神经元组织特征。因此，微电极在神经工程领域有着广泛的潜在应用。然而，人们对微电极产生的电流密度和电场了解甚少。本项目的目标是使用几何和电学精确的有限元模型，回答关于金属微电极电刺激的三个基本问题。第一，电极表面电流密度的空间分布是怎样的？第二，电极几何形状的改变如何影响神经兴奋？第三，在什么条件下有限尺寸的电极可以被建模为点源？模型分析表明，电流密度集中在微电极的尖端和电极-绝缘界面处。改变电极的表面积、电极尖端的曲率半径或在电极表面施加电阻涂层会改变电极表面的电流密度分布。电极几何形状的改变对神经兴奋模式影响不大，对于距离电极尖端大于约50微米的情况，使用理论点源对尖锐尖端微电极产生的电场进行建模是有效的。本研究结果表明，使用相对较大表面积（500 - 1000平方微米）、相对钝的尖端（曲率半径3 - 6微米）以及薄的（约1微米）中等电阻涂层（约50欧姆米）的电极，可以在电极表面实现近乎均匀的电流密度分布。
