The Effect of Source Extension on the Location and Components of the Equivalent Dipole

Abstract

Evoked potentials and Electroencephalograms can be used to determine the location of brain activity and the direction of the polarity. For this purpose mathematical models are used in which the various regions in the head with different conductivity are represented by generalized forms like spheres and spheroids. In most models the source is described by a mathematical point dipole. Since there exists a one-to-one correspondence between visual field and area 17 of the visual cortex, in many evoked potential experiments with visual stimuli the size of the stimulus field is chosen as small as possible in order to activate only a small part of the cortex. In this way a point dipole is imitated at the cost of a lower signal-to-noise ratio.