Srinivasan R, Nunez P L, Silberstein R B
Department of Psychology, University of Oregon, Eugene 97403-1227, USA.
IEEE Trans Biomed Eng. 1998 Jul;45(7):814-26. doi: 10.1109/10.686789.
The spatial statistics of scalp electroencephalogram (EEG) are usually presented as coherence in individual frequency bands. These coherences result both from correlations among neocortical sources and volume conduction through the tissues of the head. The scalp EEG is spatially low-pass filtered by the poorly conducting skull, introducing artificial correlation between the electrodes. A four concentric spheres (brain, CSF, skull, and scalp) model of the head and stochastic field theory are used here to derive an analytic estimate of the coherence at scalp electrodes due to volume conduction of uncorrelated source activity, predicting that electrodes within 10-12 cm can appear correlated. The surface Laplacian estimate of cortical surface potentials spatially bandpass filters the scalp potentials reducing this artificial coherence due to volume conduction. Examination of EEG data confirms that the coherence estimates from raw scalp potentials and Laplacians are sensitive to different spatial bandwidths and should be used in parallel in studies of neocortical dynamic function.
头皮脑电图（EEG）的空间统计通常以各个频段的相干性来呈现。这些相干性既源于新皮质源之间的相关性，也源于通过头部组织的容积传导。头皮EEG在空间上被导电性差的颅骨进行低通滤波，从而在电极之间引入了人为的相关性。这里使用头部的四同心球（脑、脑脊液、颅骨和头皮）模型以及随机场理论，来推导由于不相关源活动的容积传导而在头皮电极处产生的相干性的解析估计值，预测在10 - 12厘米范围内的电极可能会显示出相关性。皮质表面电位的表面拉普拉斯估计在空间上对头皮电位进行带通滤波，减少了由于容积传导引起的这种人为相干性。对EEG数据的检查证实，来自原始头皮电位和拉普拉斯变换的相干性估计对不同的空间带宽敏感，并且在新皮质动态功能研究中应并行使用。
