Chaos of plethysmogram in relation to scalp-EEG: a model and experiments

Abstract

We studied a relation of chaotic dynamics of finger plethysmogram to scalp-EEG in both theoretical and experimental approaches. We proposed a mathematical model to describe emergence of chaos in finger tip pulse wave, which gave a theoretical prediction indicating increased chaoticity in higher cerebral centre leading to an increase of chaos dynamics in plethysmograms. We designed an experiment to observe scalp-EEG and finger plethysmogram using two mental tasks to validate the relationship. We found that scalp-EEG showed an increase of the largest Lyapunov exponents (LLE) during speaking certain voices. Topographical scalp map of LLE showed enhanced arise around occipital and right cerebral area. Whereas, there was decreasing tendency during listening music, where LLE scalp map revealed a drop around centre cerebral area. The same tendency was found from finger plethysmograms under the same tasks. The experiment gave results that agreed well with the theoretical relation derived from our proposed model.