Effects of holes on EEG forward solutions using a realistic geometry head model.

Holes in the skull and the scalp are associated with intracranial monitoring procedures. The purpose of the present study is to evaluate the effects of holes on extracranial electroencephalogram (EEG) and intracranial electrocorticogram (ECoG) recordings. The finite difference method (FDM) was used to model the head volume conductor with a hole of varying size. A current dipole was used to simulate the brain electrical activity with varying locations within the brain. The effects of the holes were assessed by comparing the forward potential distributions with and without a hole. The present computer simulation results indicate that the effect of a hole on the scalp EEG and ECoG recordings strongly depends on the dipole location and orientation. For a superficial radial dipole located under a hole of radius ranging from 5 mm to 40 mm, the relative error (RE) varies from 0.99% to 93.07% for the EEG and from 0.025% to 16.72% for the ECoG. The correlation coefficient (CC) varies from 99.99% to 21.1% and from 100% to 99.75% for the EEG and EcoG, respectively. For radial dipoles, the strongest effect on the EEG and ECoG occurs when the dipole is located below the center of the hole, while for tangential dipoles, the strongest effect occurs when the dipole is located below the border of the hole. The effect of a hole on the EEG is much larger than upon the ECoG.