CORRELATION BETWEEN SOURCE ASYMMETRY AND SCALP POTENTIAL ASYMMETRY INA PROLATE SPHEROID MODEL OF THE HEAD

The correlation between electric source asymmetry in the brain and pot ential amplitude asymmetry developed on the scalp was investigated usi ng a computerized analytical prolate spheroid model of the head. The s ource was modeled by a single current dipole located in the occipital region of the brain. The potential created by the dipole was calculate d using Laplace's equation with boundary conditions while allowing a q uasi-static formulation and linear media. The dipole was located in th e inner part of a four-compartment medium representing the scalp, the skull (with non-isotropic conduction), the cerebrospinal fluid (CSF), and the cortex. The asymmetry was modeled by a dipole located with an angle to the major axis connecting the nasion and the inion. The prese nt study shows that source asymmetry can cause non-negligible asymmetr ies in the potential amplitude measured on the scalp above homotopic p oints of the two hemispheres. A potential asymmetry of up to 15% in th e O-1-O-2 pair of electrodes was found when the dipole is rotated from the symmetric major axis at an angle of 10 degrees. The source asymme try in the occipital region can be related to fair deviation, which is an asymmetry present in the majority of the population. Since this as ymmetry is not related to real physiologic and psychologic sources of potential amplitude asymmetries, it should be taken under consideratio n when potential distribution analysis is performed. (C) 1997 Elsevier Science Ltd.