Skrandies W
Max-Planck-Institute for Physiological and Clinical Research, Bah Nauheim, F.R.G.
Brain Topogr. 1990 Fall;3(1):137-41. doi: 10.1007/BF01128870.
Multichannel recordings are commonly presented as topographic maps series displaying the change of the potential distribution over time. When reviewing a sequence of potential maps it becomes obvious that there are epochs with only little activity (few field lines; small extrema values) while at other times the fields display high peaks and deep troughs with steep gradients. The measure of global field power (GFP) corresponds to the spatial standard deviation, and it quantifies the amount of activity at each time point in the field considering the data from all recording electrodes simultaneously resulting in a reference-independent descriptor of the potential field. Global field power is plotted as a function of time, and the occurrence times of GFP maxima are used to determine the latencies of evoked potential components. The topographical change occurring in subsequent potential field distributions may also be quantified by computing an index of global dissimilarity. Global field power and global dissimilarity show a complementary behavior over time: in general, high GFP is associated with similar fields while during periods between GFP peaks the topographic patterns of successive field distributions change rapidly accompanied by high dissimilarity values. The topographic changes, however, are best recognized by a segmentation procedure that considers field structure independent of GFP and global dissimilarity. The principles and practical applications of GFP computation, component latency determination and global dissimilarity of potential field distributions as well as a topographical time segmentation procedure will be illustrated with multichannel data evoked by visual stimuli.
多通道记录通常以地形图系列的形式呈现，展示电位分布随时间的变化。在查看一系列电位图时，很明显存在活动很少的时期（场线少；极值小），而在其他时候，场显示出具有陡峭梯度的高峰值和深谷值。全局场功率（GFP）的度量对应于空间标准差，它同时考虑来自所有记录电极的数据，量化了场中每个时间点的活动量，从而得到一个与参考无关的电位场描述符。全局场功率作为时间的函数绘制，GFP最大值的出现时间用于确定诱发电位成分的潜伏期。后续电位场分布中发生的地形变化也可以通过计算全局差异指数来量化。全局场功率和全局差异随时间呈现互补行为：一般来说，高GFP与相似的场相关，而在GFP峰值之间的时间段内，连续场分布的地形模式变化迅速，同时伴有高差异值。然而，地形变化最好通过一种分割程序来识别，该程序考虑与GFP和全局差异无关的场结构。将用视觉刺激诱发的多通道数据来说明GFP计算、成分潜伏期确定和电位场分布的全局差异以及地形时间分割程序的原理和实际应用。
