Non-equilibrium critical dynamics of bursts in [theta] and [delta] rhythms as fundamental characteristic of sleep and wake micro-architecture

Origin and functions of intermittent transitions among sleep stages, including short awakenings and arousals, constitute a challenge to the current homeostatic framework for sleep regulation, focusing on factors modulating sleep over large time scales. Here we propose that the complex micro-architecture characterizing the sleep-wake cycle results from an underlying non-equilibrium critical dynamics, bridging collective behaviors across spatio-temporal scales. We investigate [theta] and [delta] wave dynamics in control rats and in rats with lesions of sleep-promoting neurons in the parafacial zone. We demonstrate that intermittent bursts in [theta] and [delta] rhythms exhibit a complex temporal organization, with long-range power-law correlations and a robust duality of power law ([theta]-bursts, active phase) and exponential-like ([delta]-bursts, quiescent phase) duration distributions, typical features of non-equilibrium systems self-organizing at criticality. Crucially, such temporal organization relates to anti-correlated coupling between [theta]- and [delta]-bursts, and is independent of the dominant physiologic state and lesions, a solid indication of a basic principle in sleep dynamics.