Analysis of magnetoencephalographic data using the homogeneous sphere model: empirical tests.

ABSTRACT

The external magnetic fields produced by artificial current dipoles placed in conducting-gel filled spheres, partial spheres and human skulls have been measured. Using a homogeneously conducting sphere model, the dipole parameters have been estimated. Although good quality data fitting is obtainable for a range of positions of the centre of the sphere used in the modelling, the predictions for the dipole obtained with those different assumed positions differ considerably. It is found that the most reliable method of obtaining accurate estimates of the dipole parameters is by taking an average of the predictions of several of the best-fit analyses. The information about the accuracy of the predictions that is obtainable from the fitting routine's residual error parameter is discussed.