Effect of Reference Electrode Configuration on the Estimation of Neuronal Generators of Cortical Auditory Evoked Potential in Young Adults

This research analyzed the brain generators of Cortical Auditory Evoked Potentials (CAEP) based on the reference electrode system used during electroencephalogram (EEG) acquisition. This type of evoked potential is highly relevant in audiology, both from an experimental and clinical perspective, as it allows monitoring the effectiveness of therapies and interventions related to auditory function recovery and speech acquisition/comprehension. Therefore, it is crucial to develop analysis methods that, based on EEG, accurately estimate the cortical activation map associated with CAEP generation. Considering that the reference electrode system affects the amplitude and morphology of CAEP, does it also influence the cortical activation map associated with its generation? We analyzed the CAEP of 26 young, right-handed, normal-hearing adults to answer this question. The EEG was acquired from 64 scalp locations. The electrodes were placed according to the international 10-20 system. Subsequently, four reference systems were tested: the average of the mastoids, the average of all electrodes, Cz, and the average of two electrodes positioned on frontal areas (the frontal average). An inverse solution method for EEG (LORETA) was employed to convert voltages recorded on the scalp into electrical currents in the brain, generating cortical activation maps.To determine the most suitable reference type, we consider it a ground truth that cortical maps should accurately reflect activation in the temporal lobe, ideally in the primary auditory cortex. The results illustrated that the CAEP cortical activation map depended on the choice of reference system for the EEG acquisition. The most suitable reference configuration for the study of CAEP was the average reference, followed by the average of central electrodes and the average of mastoids. The least suitable was the Cz reference. These findings contribute to developing speech therapy tools to have markers of brain activity as a clinical criterion for selecting cochlear implant candidates and monitoring brain maturation processes and speech-related speech therapy interventions.