Discussion on “Towards a quantitative characterization of functional states of the brain: from the non-linear methodology to the global linear description” by J. Wackermann

Wackermann (1999) [Wackermann, J., 1999. Towards a quantitative characterization of functional states of the brain: from the non-linear methodology to the global linear description. Int. J. Psychophysiol. 34, 65-80] proposed ∑-ϕ-Ω system for describing the global brain macro-state, in which Ω complexity was used to quantify the degree of synchrony between spatially distributed EEG processes. In this paper the effect of signal power on Ω complexity is discussed, which was not considered in Wackermann's paper (1999). Then an improved method for eliminating the effect of signal power on Ω complexity is proposed. Finally a case study on the degree of synchrony between two-channel EEG signals over different brain regions during hand motor imagery is given. The results show that the improved Ω complexity measure would characterize the true degree of synchrony among the EEG signals by eliminating the influence of signal power.