Effect of hyperoxia on oscillatory brain states in waking and asleep humans

Abstract

The major question addressed by neuroscience is how behavior can be explained through knowledge of the brain. Given the unobservable nature of mind, cognitive neuroscientists depend on observations of the electrical activity of the brain gleaned through electroencephalographic (EEG) recordings to track gross changes in brain state across multiple levels of behavioral state – from alert wakefulness to deep sleep. Briefly, shifts towards vigilance or arousal are accompanied by a shift towards faster frequencies of neural oscillations in the brain, whereas shifts towards inactivity are accompanied by a preponderance of slower brain rhythms. Brain processing is highly dependent on oxidative metabolism, however studies in rats have shown that the administration of 100% oxygen gas (hyperoxia) results in a paradoxical shift toward more deactivated brain states during both anesthesia and natural sleep. The research here presented was conducted to ascertain if similar effects of hyperoxia are present in awake and sleeping humans. Experiment 1 administered 100% oxygen gas or normal air to participants who were performing an eyes-opened/eyes-closed resting state task. Hyperoxia was associated with decreases in alpha, beta, and gamma oscillations when the eyes were opened, and decreases in beta and increases in delta oscillations when the eyes were closed. We also observed that hyperoxia increased the magnitude of the eyes-opened/eyes-closed state transition. Experiment 2 administered 100% oxygen gas or normal air to participants who were taking a 90-minute nap. Hyperoxia was associated with minor decreases in alpha oscillations in the Wake and N1 stage and increases in theta oscillations in the N2 stage. Taken together, these studies reveal a more complex influence of hyperoxia on EEG oscillations, where high-frequency oscillations are attenuated in some brain states, and low-frequency oscillations are enhanced in others.