| Abstract: | We have studied topographical differences in averaged EEG amplitudes in alpha domain recorded in 10–20 system during “eyes closed” test. These differences appeared due to the use of 13 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 individual ear electrodes (A12, Sym, A1, A2); vertex (Cz); and averaged reference (AR). Six experiments for each of the ten subjects were carried out with grounded and ungrounded states of three distant basic references P2, C, and 2Sh. Pairwise comparisons of topographic consistency of 13 reference schemes were carried out on the proposed complex of three independent indicators with evaluative criterion, followed by centroid-based clustering of the reference schemes and its discriminant verification. As a result, we have established (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) no significant reasons have been found for preferring a grounded (neutral) states of reference electrodes, that makes the search for or mathematical construct of an infinitely remote neutral reference electrode less important. |
