Investigating the effect on whole brain functional connectivity at different sedation depth induced by nitrous oxide

Abstract

Although functional connectivity has received great attention in consciousness study area, only few studies have investigated functional connectivity limited to sedation state where consciousness is maintained but impaired. The aim of the present study was to investigate the changes in functional connectivity of parietal-frontal network resulting from nitrous oxide induced sedation state, and determine the neural correlates of cognitive impairment during transition states of consciousness. Electroencephalography was acquired from healthy adult patients with nitrous oxide inhalation to induce cognitive impairment, and analyzed by using Granger Causality (GC). The periods of awake, sedation and recovery for GC between frontal and parietal areas in delta, theta, alpha, beta, gamma and time-domain frequency band were obtained. Kruskal-Wallis test with post-hoc analysis was conducted for GC values of each period for comparison. As sedative state was induced by nitrous oxide inhalation, the power in low frequency band showed increased activity in frontal regions, which was reversed with discontinuation of nitrous oxide. The feedback and feedforward connections analyzed in spectral GC were differently changed in accordance with EEG frequency bands in sedative state by nitrous oxide administration. Calculated spectral GC of high frequency region in frontal to parietal direction was significantly decreased in sedative state while the spectral GC in reverse direction did not show significant change. The frontal-parietal functional connectivity is significantly affected by nitrous oxide inhalation. It is suggested that the significantly decreased frontal to parietal interaction may induce sedative state which can be described as impaired consciousness in accordance with the same directional decrease of interaction in the loss of consciousness induced by anesthetics.