New research in rats shows that cortical arousals and brief awakenings during sleep exhibit non-equilibrium dynamics and complex organization across time scales necessary for spontaneous sleep-stage transitions and for maintaining healthy sleep.
Prof. Plamen Ch. Ivanov of Boston University and colleagues present these findings in PLOS Computational Biology.
Sleep is traditionally considered to be a homeostatic process that resists deviation from equilibrium. In that regard, brief episodes of waking are viewed as perturbations that lead to sleep fragmentation and related sleep disorders. While addressing aspects of sleep regulation related to consolidated sleep and wake and the sleep-wake cycle, the homeostatic paradigm does not account for the dozens of abrupt sleep-stage transitions and micro-states within sleep stages throughout the night. Ivanov and colleagues hypothesized that, while sleep is indeed homeostatic at time scales of hours and days, non-equilibrium dynamics and criticality underlie sleep micro-architecture at shorter time scales.
To test this hypothesis, the researchers collected electroencephalogram (EEG) recordings of brain activity over multiple days in normal rats and in rats with injuries to the parafacial zone, a brain region that helps regulate sleep. They analyzed the bursting dynamics of brain activity patterns known as theta waves and delta waves, which are seen in both sleeping rats and humans.