Mechanism of Flux Reversal Phenomena in Spatial Distributions of the Magnetoencephalograms

Abstract

It is difficult to solve the inverse problem in magnetoencephalography because of complexity of electrical sources and inhomogeneities of electrical conductivities in the head. The head consists of different materials with different electrical conductivities such as brain tissues, skull and ventricles. We have investigated the influence of small inhomogeneous regions in the head on spatial patterns of surface magnetic fields, and we have demonstrated that the flux reversal phenomena can be observed in special cases where conductivities of the inhomogeneous regions change with pathological situations (Ueno et al. 1985). A current dipole which orients radially in a homogeneous sphere produces no magnetic fields outside the sphere (Baule et al. 1965). We have also reported that radially oriented dipoles produce magnetic fields outside the sphere when inhomogeneous regions exist inside the sphere (Ueno et al. 1987, Iramina et al. 1988). The present study is focused on the mechanism of flux reversal phenomena which can be observed in spatial distributions of the magnetoencephalograms (MEGs). Computer simulation shows that the flux reversal can be caused by the change of flow patterns of currents which flow on the surface of boundary between different inhomogeneous regions in the head.