Study on Optimal Choice of a Reference Electrode for EEG Recording

During a "eyes closed" test, we looked at topographical differences in averaged EEG amplitudes in the alpha domain recorded in the 10–20 system. These discrepancies arose as a result of the usage of 13 different reference schemes: top and bottom of the chin (P1, P2); nose (N); top and bottom of the back of the neck (Sh1, Sh2); upper back (C); united electrodes at the base of the neck anteriorly and posteriorly (2Sh); united, ipsilateral, and individ- ual ear electrodes (A12, Sym, A1, A2); vertex (Cz); and averaged reference (AR). Six experiments with grounded and ungrounded states of three distant fundamental references P2, C, and 2Sh were conducted for each of the ten subjects. On the proposed complex of three independent indicators with evaluative criterion, pairwise evaluations of topographic consistency of 13 reference schemes were carried out, followed by centroid-based clus- tering of the reference schemes and its discriminant verification. As a result, we've made some progress(1) that most coordinated topography is provided by the following reference electrodes—A12, P1, P2, Sym; (2) reference electrodes A1, Sh2, A2, Sh1, AR, Cz are characterized by individually varying topography, which may lead to contradictory conclusions obtained when they are used; (3) There have been no substantial reasons for assuming a grounded (neutral) state of reference electrodes, making the search for or mathematical construct of an indefinitely remote neutral reference electrode less important.