Critical dynamics in bursts of δ and θ-rhythms across the sleep-wake cycle

Solid evidences indicate that different cortical rhythms characterize distinct phases (sleep stages) of the sleep-wake cycle. Sleep stages are not stable, and sleep periods exhibit numerous transitions among different stages, including short awakenings/arousals. Nature and dynamics of such transitions, as well as origin and functions of arousals, remain elusive. Recently, it has been shown that brief awakenings/arousals do not have a characteristic duration and consistently follow a power-law distributions across different species. Since arousals can be viewed as 'active' states of the brain that interrupt the 'inactive' phase represented by sleep periods, such a scale-free statistics has been interpreted as a fingerprint of criticality in sleep dynamics, suggesting that arousals are an integral part of sleep regulation. In this talk, I will present recent results on the dynamics of relevant cortical rhythms across the sleep-wake cycle that seem to support such a hypothesis. I will show that wake-related θ- and sleep-related δ-bursts exhibit a robust scale invariant temporal organization closely reminiscent of other non-equilibrium phenomena, and discuss their dynamics and coupling in relation to the neuronal circuitry responsible for wake and sleep control in rats.