Bedard Claude, Gomes Jean-Marie, Bal Thierry, Destexhe Alain
UNIC, CNRS, Gif sur Yvette, France.
J Integr Neurosci. 2017;16(1):3-18. doi: 10.3233/JIN-160001.
In this viewpoint article, we discuss the electric properties of the medium around neurons, which are important to correctly interpret extracellular potentials or electric field effects in neural tissue. We focus on how these electric properties shape the frequency scaling of brain signals at different scales, such as intracellular recordings, the local field potential (LFP), the electroencephalogram (EEG) or the magnetoencephalogram (MEG). These signals display frequency-scaling properties which are not consistent with resistive media. The medium appears to exert a frequency filtering scaling as 1/f, which is the typical frequency scaling of ionic diffusion. Such a scaling was also found recently by impedance measurements in physiological conditions. Ionic diffusion appears to be the only possible explanation to reconcile these measurements and the frequency-scaling properties found in different brain signals. However, other measurements suggest that the extracellular medium is essentially resistive. To resolve this discrepancy, we show new evidence that metal-electrode measurements can be perturbed by shunt currents going through the surface of the brain. Such a shunt may explain the contradictory measurements, and together with ionic diffusion, provides a framework where all observations can be reconciled. Finally, we propose a method to perform measurements avoiding shunting effects, thus enabling to test the predictions of this framework.
在这篇观点文章中，我们讨论了神经元周围介质的电学性质，这些性质对于正确解释神经组织中的细胞外电位或电场效应至关重要。我们重点关注这些电学性质如何在不同尺度上塑造脑信号的频率标度，比如细胞内记录、局部场电位（LFP）、脑电图（EEG）或脑磁图（MEG）。这些信号呈现出与电阻性介质不一致的频率标度特性。该介质似乎施加了一个1/f的频率滤波标度，这是离子扩散的典型频率标度。最近在生理条件下通过阻抗测量也发现了这样的标度。离子扩散似乎是调和这些测量结果与在不同脑信号中发现的频率标度特性的唯一可能解释。然而，其他测量表明细胞外介质本质上是电阻性的。为了解决这一差异，我们展示了新的证据，即金属电极测量可能会受到流经脑表面的分流电流的干扰。这样的分流可能解释了相互矛盾的测量结果，并且与离子扩散一起提供了一个能调和所有观测结果的框架。最后，我们提出了一种避免分流效应进行测量的方法，从而能够检验该框架的预测。
