Evaluation of brain functional states based on projections of electroencephalographic spectral parameters on 2-dimensional canonical space

► Canonical reference spaces are constructed from EEG parameters by factor analysis. ► Two statistical measures, Mahalanobis distance and Hellinger distance, are derived. ► The measures evaluate state-discriminating ability of the reference space. ► The measures are well correlated with sleep-wake durations after caffeine. ► Two statistical measures can describe vigilance and drug-induced states.