The resistive or non-resistive nature of the extracellular space in the brain is still debated, and is an important issue for correctly modeling extracellular potentials. Here, we first show theoretically that if the medium is resistive, the frequency scaling should be the same for electroencephalogram (EEG) and magnetoencephalogram (MEG) signals at low frequencies (<10 Hz). To test this prediction, we analyzed the spectrum of simultaneous EEG and MEG measurements in four human subjects. The frequency scaling of EEG displays coherent variations across the brain, in general between 1/f and 1/f (2). In a given region, although the variability of the frequency scaling exponent was higher for MEG compared to EEG, both signals consistently scale with a different exponent. In some cases, the scaling was similar, but only when the signal-to-noise ratio of the MEG was low. Several methods of noise correction for environmental and instrumental noise were tested, and they all increased the difference between EEG and MEG scaling. In conclusion, there is a significant difference in frequency scaling between EEG and MEG, which can be explained if the extracellular medium (including other layers such as dura matter and skull) is globally non-resistive.

中文翻译：

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对人类同步脑电图和脑磁图记录的比较功率谱分析表明非电阻性细胞外介质：EEG 和 MEG 功率谱。


大脑细胞外空间的电阻性或非电阻性仍然存在争议，并且是正确建模细胞外电位的重要问题。在这里，我们首先从理论上证明，如果介质是电阻性的，则低频（<10 Hz）下的脑电图（EEG）和脑磁图（MEG）信号的频率缩放应该相同。为了检验这一预测，我们分析了四名人类受试者同时进行脑电图和脑磁图测量的频谱。 EEG 的频率缩放显示整个大脑的连贯变化，通常在 1/f 和 1/f 之间 (2)。在给定区域中，尽管 MEG 的频率缩放指数的变异性高于 EEG，但两个信号始终以不同的指数缩放。在某些情况下，缩放是相似的，但仅当 MEG 的信噪比较低时。测试了几种针对环境和仪器噪声的噪声校正方法，它们都增加了脑电图和脑磁图缩放之间的差异。总之，EEG 和 MEG 之间的频率缩放存在显着差异，如果细胞外介质（包括硬脑膜和颅骨等其他层）全局无电阻，则可以解释这一点。