Artifacts EEG during Dense Array EEG (256 channels) acquisition: a comparisons with the 10-20 standard system.

Purpose In order to better differentiate between what is genuine neuronal activity and what is not, we deploye a method to better understand the topographic field distribution of EEG artifacts i.e.the 256 channel EEG. Because of the profuse number of zygomatic, sovraorbitary, upper cervical and upper margin jaw electrodes, we can better distinguish the artifacts’ sources. We focus on a Topo Plot Map montage i.e. a projection of each electrode’s activity on a scalp model. Methods We measured first the head circumference finding the vertex (Cz, 10-20 system). The applied net arranges the electrodes across the surface of head and face, with an interelectrode distance in the range of 20 to 25 mm. Electrodes were located in a plastic pedestal with an Ag/Cl basis covered by little sponges, soaked in a physiological-potassium- shampoo solution for about 5 minutes. The sampling rate was 250 Hz, interelectrode impedance below 100 Kohms, acquisition reference was at vertex, band pass filter 0.03-70 Hz, 7,5 MicronVolts sensitivity,50 Hz Notch filter avoiding noise interferences. Results Physiological artefacts were eye movements (horizontal and vertical blinking) with antero posterior topography, ballistogram with temporal topography, mouth movements and chewing with maximal activity over the zygomatic electrodes, occipital or temporal EMG activity. Non physiological artefacts were the electrolyte bridges, the digital filters artefacts, the 50 hz current artefact .Visual comparison for each of these artefacts was performed between bipolar 10-20 standard system montage and 256 Topo Plot Map, in order to define the recognition of field potential sources and topographic distribution.