Date of Award

Spring 2006

Document Type


Degree Name

Doctor of Philosophy (PhD)


Biomedical Engineering

First Advisor

Walter A. Besio


Brain activity generates electrical potentials that are spatio-temporal in nature. Electroencephalography (EEG) is the least costly and most widely used non-invasive technique for diagnosing many brain problems. It has high temporal resolution but lacks high spatial resolution.

The surface Laplacian will enhance the spatial resolution of EEG as it performs the second spatial derivative of the surface potentials. In an attempt to increase the spatial selectivity, researchers introduced a bipolar electrode configuration using a five point finite difference method (FPM) and others applied a quasi-bipolar (tri-polar with two elements shorted) concentric electrode configuration. To further increase the spatial resolution, the nine-point finite difference method (NPM) was generalized to tri-polar concentric ring electrodes.

A computer model was developed to evaluate and compare the properties of concentric bipolar, quasi-bipolar, and tri-polar electrode configurations, and the results were verified with tank experiments. The tri-polar configuration was found to have significantly improved spatial localization.

Movement-related potential (MRP) signals were recorded from the left pre-frontal lobes on the scalp of human subjects while they performed fast repetitive movements. Disc, bipolar, quasi-bipolar, and tri-polar electrodes were used. MRP signals were plotted for all four electrode configurations. The SNR of four electrode configurations were studied and statistically analyzed using Bonferroni statistical tests.

MRP signals were recorded from an array of 5X7 on the left hemisphere of the head. The SNR, spatial selectivity, and mutual information (MI) were compared among conventional disc electrodes, bipolar and tri-polar concentric ring electrodes. The tri-polar concentric electrodes showed more significant improvement in SNR than the all other electrode systems tested. Tri-polar concentric electrodes also had significantly higher spatial selectivity and spatial attenuation for global signals. The increased spatial selectivity significantly decreased the MI in between different channels which will be useful in different BCI system.

The tri-polar and bipolar concentric ring electrode configuration was also shown to be appropriate for recording seizure electrographic activity. This higher spatial selectivity of tri-polar concentric electrodes may be useful for seizure foci detection and seizure stage determination.