Topological specificity of VEP responses: a comparison of tripolar and traditional electrodes

Due to the overall spread of the ionic currents from the underlying dipolar sources, achieving high spatial resolution, and in turn accurate source estimation, is difficult with standard EEG electrode arrays. However, tripolar concentric ring electrodes (tCREs) have been shown to be more useful in extracting unique information from scalp potentials than traditional electrodes as revealed by investigations of source localization of epileptiform activity, decoding of real versus imaginary motor signals, and assessment of high frequency oscillations and other brain rhythms in humans. It has been reported that individual tCREs through focal laplacian estimation are better able to localize signals than even a cluster of traditional electrodes. Here, we used a small array of six tCREs to assess the specificity of the information available from individual neighboring electrodes when stimulating partial fields of vision. We employed large checkerboard patterns comprising 1° checks, reversing at 4 hz. Subjects were instructed to fixate in one of seven locations (each corner, right side, left side, and center). We compared these responses with those collected in a traditional mode in the same array. Our findings reveal that responses from individual tCREs are distinctly unique from the responses of neighboring electrodes. Conversely, the traditional EEG signals yielded nearly identical waveforms, highlighting the known limitations of traditional methods. We also found that in contrast to traditional electrodes, the unique information provided by the tCREs provided unambiguous gross localization of the response.