Volume conduction of electrical potentials in the brain is highly influenced by the material properties and geometry of the tissue and recording devices implanted into the tissue. These effects are very large in EEG due to the volume conduction through the skull and scalp but are often neglected in intracranial electrophysiology. When considering penetrating electrodes deep in the brain, the assumption of an infinite and homogenous medium can be used when the sources are far enough from the brain surface and the electrodes to minimize the boundary effect. When the electrodes are recording from the brain's surface the effect of the boundary cannot be neglected, and the large surface area and commonly used insulating materials in surface electrode arrays may further increase the effect by altering the nature of the boundary in the immediate vicinity of the electrodes. This gives the experimenter some control over the spatial profiles of the potentials by appropriate design of the electrode arrays. We construct a simple three-layer model to describe the effect of material properties and geometry above the brain surface on the electric potentials and conduct empirical experiments to validate this model. A laminar electrode array is used to measure the effect of insulating and relatively conducting layers above the cortical surface by recording evoked potentials alternating between a dried surface and saline covering layer, respectively. Empirically, we find that an insulating boundary amplifies the potentials relative to conductive saline by about a factor of 4, and that the effect is not constrained to potentials that originate near the surface. The model is applied to predict the influence of array design and implantation procedure on the recording amplitude and spatial selectivity of the surface electrode arrays.

中文翻译：

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脑表面边界条件对电生理学的影响和对脑电图的影响

大脑中电势的体积传导受到组织的材料特性和几何形状以及植入组织中的记录装置的高度影响。由于通过颅骨和头皮的体积传导，这些影响在 EEG 中非常大，但在颅内电生理学中经常被忽略。当考虑在大脑深处穿透电极时，当源距离大脑表面和电极足够远以最小化边界效应时，可以使用无限且均匀介质的假设。当电极从大脑表面记录时，边界的影响不容忽视，并且表面电极阵列中的大表面积和常用的绝缘材料可以通过改变紧邻电极的边界的性质来进一步增加效果。这使实验者可以通过适当设计电极阵列来控制电位的空间分布。我们构建了一个简单的三层模型来描述大脑表面上方的材料特性和几何形状对电势的影响，并进行实证实验来验证该模型。层状电极阵列用于通过分别记录干燥表面和盐水覆盖层之间交替的诱发电位来测量皮质表面上方的绝缘层和相对导电层的效果。根据经验，我们发现绝缘边界将相对于导电盐水的电位放大了大约 4 倍，并且该效果不受限于源自表面附近的电位。该模型用于预测阵列设计和植入程序对表面电极阵列的记录幅度和空间选择性的影响。