Optimal electrode placements for adequate spatial sampling of auditory evoked potentials

When evoked responses are used in clinical practice and research the measures that are most commonly considered are the latencies and amplitudes of EP components as measured at a single electrode site. Our recent studies have shown that multichannel recordings yield measures such as potential field asymmetry that may be as important as component latency and amplitude. The purpose of this short technical note is to suggest that electrode placement is critical for demonstrating interesting features of the potential field topography, specifically, bilateral, homologous generator sites. The cortical imaging technique (CIT) was used to analyze the averaged responses for a group of thirty normal young adults to a repeated tone and a random oddball tone. Recordings were obtained at 28 scalp recording sites which included 20 placements from the 10-20 system and eight additional sites. Simulated cortical maps were derived for four components, the N1 frequent response and the N2a, P3, and N3, rare minus frequent responses for three different electrode arrays. These arrangements included the full 28-channel array, a 20-channel array that excluded eight additional central sites, and a 20-channel array that included the eight additional sites and excluded peripheral sites. This study demonstrates that for these auditory paradigms, the placement of the electrodes is critically important for discriminating important features of the potential fields.