Desmedt J E, Chalklin V, Tomberg C
Brain Research Unit, University of Brussels, Belgium.
Electroencephalogr Clin Neurophysiol. 1990 Jul-Aug;77(4):243-58. doi: 10.1016/0168-5597(90)90063-j.
In brain topographic mapping, the putative location and orientation in the head space of neural generators are currently inferred from the features of negative and positive scalp potential fields. This procedure requires the use of a fairly neutral reference. The frequently advocated average reference creates problems because its effect is not merely to change a (steady) zero reference level, but to dynamically zero-center all scalp potentials at each latency. Ghost potential fields are thus created at the latencies for which the integral of scalp recorded potentials differs from zero. These distortions of brain mapping have been analyzed with a true 3-shell head model in conjunction with the emulation of SEP components. In the head model, surface potential fields generated by dipoles or dipole sheets of various depths and orientations were computed either over the north hemisphere, so as to emulate scalp recorded SEP components, or over the entire equivalent head sphere. The spurious effects of the average reference are shown to occur because it is computed from a limited number of (scalp) electrodes which fail to survey the bottom half of the head.
在脑地形图绘制中，目前神经发生器在头部空间的假定位置和方向是根据头皮正负电位场的特征推断出来的。这个过程需要使用一个相当中性的参考。经常被提倡的平均参考会产生问题，因为它的作用不仅仅是改变一个（稳定的）零参考水平，而是在每个潜伏期动态地将所有头皮电位归零。因此，在头皮记录电位的积分不为零的潜伏期会产生虚假电位场。已经结合SEP成分的模拟，用一个真实的三层头部模型分析了脑图谱的这些畸变。在头部模型中，计算了由不同深度和方向的偶极子或偶极子片产生的表面电位场，要么在北半球上计算，以模拟头皮记录的SEP成分，要么在整个等效头部球面上计算。平均参考的虚假效应被证明是由于它是从有限数量的（头皮）电极计算出来的，这些电极无法探测到头部的下半部分。
