Scalp potentials and magnetic fields of a fully and partially activated central sulcus

Our objective was to examine how the scalp potentials and the magnetic fields of a sulcus change if the cortex in the walls is partially or fully active. The scalp potentials and magnetic fields of a part of the central sulcus were simulated with a finite element model of the head constructed from the segmented MRI images of an adult male subject. The electrical activity was modeled with current dipoles (0.1 mA meter) oriented perpendicular to the curved cortical surface. The fields of scalp EEG were computed using an adaptive finite element solver. The magnetic fields at a surface 1.0 cm above the scalp were computed using Biot-Savart law. Three distributions of activity were studied: the total sulcus; the superficial half and the deep half. Contour plots of EEG and MEG were constructed for each case. The spatial patterns of the scalp potential contours were significantly different for the partial vs. full activation. Each partial activation gave a uniquely different configuration of peak MEG and EEG locations that could have diagnostic utility. The spatial shifts in the peaks were more pronounced for the MEG compared with the EEG. These results indicate that scalp potentials and fields change significantly when the electrical and magnetic manifestations of activity are selective in the walls of a sulcus.