If you are suffering from brief awakenings during sleep here’s news for you. New research on rats has shown that cortical arousals during sleep exhibit non-equilibrium dynamics and complex organisation across time scales, which are necessary for spontaneous sleep-stage transitions and for maintaining healthy sleep.The study by Prof Plamen Ch Ivanov of Boston University and his colleagues has been published in the journal of 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 hypothesised 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. “Paradoxically, we find that the ‘resting’ state of healthy sleep is maintained through bursts in cortical rhythm activity that obey similar temporal organisation, statistics, and mathematical laws as earthquakes,” Ivanov said.”Our findings serve as building blocks to better understand sleep, and could help improve the detection and treatment of sleep disorders,” the professor added.It took some time for their sleep to regulate but by the fourth week the subjects had settled into a very distinct sleeping pattern. They slept first for four hours, then woke for one or two hours before falling into a second four-hour sleep. Though sleep scientists were impressed by the study, among the general public the idea that we must sleep for eight consecutive hours persists. Much like the experience of Wehr’s subjects, these references describe a first sleep which began about two hours after dusk, followed by waking period of one or two hours and then a second sleep.
