The disturbance in dynamic property in the reconstructed state space during nitrous oxide administration

Integration of neural information could be considered a crucial element in maintaining consciousness. Although consciousness is usually maintained during sedation, strictly speaking, the sedative state is different from consciousness. Nitrous oxide (N2O) has been used widely to sedate patients for dental procedures. However, its mechanism remains unclear. The aim of this study was to analyze the extent of disturbance in the integration of brain activities during N2O administration on the basis of projection to the reconstructed state space. Electroencephalography (EEG) data were obtained from 15 patients undergoing N2O (50%) administration. The correlation dimension in the reconstructed state space was quantified and correlation dimensions were compared according to consciousness levels (awake state vs. sedative state induced by N2O). The correlation dimension of alpha and gamma band EEG in the sedative state showed statistical significance at around 15 and 5 of the embedding dimension during N2O administration. The difference was the most prominent in alpha band EEG. This result indicates that the sedative state shows a higher dimensional trajectory in the reconstructed state space that is brain band specific. These data also indicate that the dimensional dynamic property has a different pattern during sedation induced by N2O compared with that at the awake state. The disturbance in information integration may explain the mild cognitive disturbance of N2O.