Biomedical Engineering Department, University of Michigan, Ann Arbor, MI, USA.
J Neural Eng. 2011 Aug;8(4):046018. doi: 10.1088/1741-2560/8/4/046018. Epub 2011 Jun 20.
While the development of microelectrode arrays has enabled access to disparate regions of a cortex for neurorehabilitation, neuroprosthetic and basic neuroscience research, accurate interpretation of the signals and manipulation of the cortical neurons depend upon the anatomical placement of the electrode arrays in a layered cortex. Toward this end, this report compares two in vivo methods for identifying the placement of electrodes in a linear array spaced 100 µm apart based on in situ laminar analysis of (1) ketamine-xylazine-induced field potential oscillations in a rat motor cortex and (2) an intracortical electrical stimulation-induced movement threshold. The first method is based on finding the polarity reversal in laminar oscillations which is reported to appear at the transition between layers IV and V in laminar 'high voltage spindles' of the rat cortical column. Analysis of histological images in our dataset indicates that polarity reversal is detected 150.1 ± 104.2 µm below the start of layer V. The second method compares the intracortical microstimulation currents that elicit a physical movement for anodic versus cathodic stimulation. It is based on the hypothesis that neural elements perpendicular to the electrode surface are preferentially excited by anodic stimulation while cathodic stimulation excites those with a direction component parallel to its surface. With this method, we expect to see a change in the stimulation currents that elicits a movement at the beginning of layer V when comparing anodic versus cathodic stimulation as the upper cortical layers contain neuronal structures that are primarily parallel to the cortical surface and lower layers contain structures that are primarily perpendicular. Using this method, there was a 78.7 ± 68 µm offset in the estimate of the depth of the start of layer V. The polarity reversal method estimates the beginning of layer V within ±90 µm with 95% confidence and the intracortical stimulation method estimates it within ±69.3 µm. We propose that these methods can be used to estimate the in situ location of laminar electrodes implanted in the rat motor cortex.
虽然微电极阵列的发展使人们能够进入皮层的不同区域进行神经康复、神经假肢和基础神经科学研究，但要准确解释信号和操纵皮层神经元，就必须将电极阵列在分层皮层中的位置进行精确的定位。为此，本报告比较了两种在体方法，以根据（1）氯胺酮-甲苯噻嗪诱导的大鼠运动皮层场电位振荡和（2）皮质内电刺激诱导的运动阈值，来确定间隔 100 µm 的线性排列电极的位置。第一种方法基于在皮层柱的层 '高压纺锤' 中发现层状振荡的极性反转，据报道，这种极性反转出现在第四层和第五层之间的过渡区。我们数据集的组织学图像分析表明，极性反转在第五层开始下方 150.1 ± 104.2 µm 处被检测到。第二种方法比较了引起物理运动的阳极刺激与阴极刺激的皮层内微刺激电流。其依据的假设是，垂直于电极表面的神经元件优先被阳极刺激激发，而阴极刺激则激发那些具有与表面平行的方向分量的元件。使用这种方法，当比较阳极刺激与阴极刺激时，我们预计在第五层开始时会看到引起运动的刺激电流发生变化，因为上层皮层的结构主要与皮层表面平行，而下层结构主要与皮层表面垂直。使用这种方法，在第五层开始的深度估计中存在 78.7 ± 68 µm 的偏移量。极性反转方法以 95%的置信度估计第五层的开始位置在 ±90 µm 以内，而皮质内刺激方法估计其在 ±69.3 µm 以内。我们提出，这些方法可用于估计植入大鼠运动皮层的层状电极的原位位置。
