Recording cortical EEG subcortically — Improved EEG monitoring from depth-stimulation electrodes

The electroencephalogram (EEG) generated by cerebral cortex can be recorded far away from the cortex, analogous to the electrocardiogram (ECG) that can be recorded far from the heart. ECG is often seen as an artifact in EEG recordings. In this paper we demonstrate that the burst suppression pattern of EEG, which is generated by the cerebral cortex, can be recorded at a distance from the cortex with a pair of electrodes in the subthalamic nucleus and also with an electrode pair on the masseter muscle below the zygomatic arch. We then present a fundamental theoretical model which explains the currents inside and outside the cranium, which produce the EEG at these locations.