Huang J C, Nicholson C, Okada Y C
Department of Physiology and Biophysics, New York University Medical Center, New York 10016.
Biophys J. 1990 Jun;57(6):1155-66. doi: 10.1016/S0006-3495(90)82635-7.
We investigated the conditions under which inhomogeneity in electrical conductivity may significantly modify the magnetic evoked field (MEF) due to primary currents (i.e., neuronal currents) in the brain. In the case of an isolated turtle cerebellum immersed in a large bath of physiological saline, our theoretical analysis showed the cerebellar surface to significantly enhance the MEF due to a primary current, by a factor of as much as two, for experimentally determined values of the conductivities of the cerebellar tissue and saline. A further parametric investigation of the conductivity effect revealed that conductivity boundaries may significantly modify the MEF due to neuronal currents located within 1 mm of a conductivity boundary, as would be the case for active neurons near an edema, an anoxic fringe such as might occur during stroke, or a ventricle in the human head. For a stationary neural source, conductivity boundaries may modify the magnitude of its MEF without affecting its temporal waveform. However, this boundary effect was found to be small for a model geometry locally approximating cortical sources in a sulcus or a fissure, where the boundary effects from adjacent sulcal walls tend to cancel each other.
我们研究了在何种条件下，由于大脑中的初级电流（即神经元电流），电导率的不均匀性可能会显著改变磁诱发场（MEF）。在将孤立的龟小脑浸入一大浴生理盐水中的情况下，我们的理论分析表明，对于小脑组织和生理盐水的电导率的实验测定值，小脑表面会使初级电流产生的MEF显著增强，增强因子高达两倍。对电导率效应的进一步参数研究表明，电导率边界可能会显著改变位于电导率边界1毫米范围内的神经元电流所产生的MEF，就像水肿附近的活跃神经元、中风期间可能出现的缺氧边缘或人头中的脑室那样。对于静止的神经源，电导率边界可能会改变其MEF的大小而不影响其时间波形。然而，对于局部近似脑沟或脑裂中皮质源的模型几何形状，发现这种边界效应很小，因为相邻脑沟壁的边界效应往往相互抵消。
