A SIMULATION STUDY ON THE DYNAMIC CHARACTERISTICS OF NEUROMAGNETIC FIELDS USING SINGLE-MOVING-DIPOLE AND 2-FIXED-DIPOLES MODELS

Spatio-temporal characteristics of the neuromagnetic fields generated from the cortical sources, which are expressed as one or multiple equivalent current dipoles, have been studied by solving forward problems. Computer simulations combined with principal component analysis were carried out using two representative models of a single moving dipole and two fixed dipoles. Distinct field patterns of the eigenvector of the second principal component (PC) were obtained depending on the orientations of the movements in the single-dipole model, while the eigenvector of the first PC had a dipolar pattern. Similar field patterns of first and second PCs were obtained when the orientation of the connected line of two fixed dipoles and the direction of the single-dipole movement were identical. It is suggested from the simulation results that a single moving dipole is equivalent to two fixed dipoles. Field patterns of the PCs obtained from the measured auditory field responses, at around 100 ms after the onset of a vowel stimulus, were consistent with those of the simulation in the case where either the movement of the single moving dipole or the orientation of the connected line of two fixed dipoles was perpendicular to the dipole axis.