Nonlinear dynamical analysis of the effect by six stimuli on electroencephalogram.

The present study investigated the search by correlation dimension (D2) for the effect of six stimuli (sucrose, spearmint, gum-base chewing as a voluntary movement, and three combinations of these stimuli) on EEG findings. Twenty normal adult subjects received sucrose, spearmint oil, gum-base alone, and three combinations of these stimuli. EEG recordings were obtained while the subjects rested quietly with their eyes closed, as the following procedure: section I, 1 minute at rest; section II, first 5-minute recording (control record); session III, each stimulus affecting for 3 minutes; session IV, 1 minute at rest; session V, 5-minute recording (poststimulus record). The EEG activity was filtered with a 0.5 Hz high pass and a 30 Hz low pass filter. The final data (epoch) for analysis were selected from all data by our epoch inducing system, and D2 was calculated using a novel analytical program. D2 was found to increase after subjects inhaled spearmint. In contrast, D2 decreased after subject's chewed gum-base and after the combination stimuli with chewing. Furthermore, the D2 change observed after each stimulus was similar to the observed D2 changes in the theta band. These findings suggest that D2 expressed the change in EEG as a brain response after each stimulus. It was also demonstrated that the change of EEG complexity as a brain response to stimulation is related to theta rhythm that might be able to produce at the cortical limbic area. We confirmed that the change observed in the complexity in response to which the chewing stimulus relates in our present study is the model that best fits that theory of the change on complexity suggested by Stam CJ.