Mutual information of tri-polar concentric ring electrodes.

Electroencephalography (EEG) signals are spatio-temporal. EEG has very good temporal resolution but typically doesn't possess high spatial resolution. The surface Laplacian enhances the spatial resolution and selectivity of the surface electrical activity. Concentric ring electrodes have been shown to estimate the surface Laplacian directly with significantly better spatial resolution than conventional electrodes and possess spatial filtering characteristics. Movement Related potentials (MRP) were recorded using tri-polar and bipolar concentric ring electrodes as well as conventional disc EEG electrodes while the subjects were pressing a micro-switch. The electrodes were placed in an array of 35 encompassing the area between Fz-Cz-Pz-P3-T5-T3-T7-F3. Mutual information (MI) of the MRP signals recorded with the different electrode systems was compared. The MRP signals recorded with the tri-polar concentric ring electrode system have significantly less MI between locations than the other two electrode configurations tested. The decrease in MI should increase the total information available by pooling of information from independent tri-polar concentric ring electrodes. These characteristics should make tri-polar concentric electrodes beneficial for EEG applications.