Findings link healthy sleep to outbursts of brain waves that mathematically mimic earthquakes.
New studies in rats show that cortical excitations and brief awakenings during sleep indicate nonequilibrium dynamics and complex organization within time scales. necessary for spontaneous transitions in the sleep phase and for maintaining a sound sleep. Prof. Plamen Ch. Ivanov from Boston University and his colleagues present these findings in PLOS Computational Biology .
Sleep has traditionally been considered a homeostatic process that withstands equilibrium. In this regard, short episodes of waking are viewed as disturbances that lead to sleep fragmentation and related sleep disorders. While considering the aspects of sleep regulation associated with consolidated sleep and waking and the sleep-wake cycle, the homeostatic paradigm does not account for the dozens of sudden transitions in the sleep phase and micro-states throughout the sleep stages throughout the night. Ivanov and his colleagues suggested that while sleep is truly homeostatic at time scales of hours and days, nonequilibrium dynamics and criticality underlie the microarchitecture of sleep at shorter time scales.
To test this hypothesis, researchers collected electroencephalogram (EEG) recordings of brain activity over several days in normal rats and in rats with parafacial injury, a brain region that helps regulate sleep. They analyzed the disruptive dynamics of brain activity patterns, known as theta waves and delta waves, which are observed in both sleeping rats and humans.
Their empirical findings and models show that arousal from sleep is a manifestation of an inherently disequilibrium sleep regulatory mechanism related to the self-organization of neural joints. This mechanism operates on time scales of seconds and minutes and stays on track through continuous bursts of brainwave rhythms.
The study also suggests that maintaining a nonequilibrium critical state is essential for the flexibility of the sleep regulation system to spontaneously activate multiple transitions between different stages of sleep and between sleep and short waking throughout the sleep period. Such a critical state is also necessary for the complex micro-architecture of sleep, which is increasingly recognized as characteristic of sound sleep. The observed critical sleep behavior draws parallels with other nonequilibrium criticality systems, such as earthquakes.
"It is paradoxical that we find that the state of 'rest' of a sound sleep is maintained through outbursts of cortical rhythm that obey similar temporal organization, statistics, and mathematical laws such as earthquakes," says Ivanov. "Our findings serve as building blocks for a better understanding of sleep and can help improve the detection and treatment of sleep disorders."
Reference: "The nonequilibrium critical dynamics of outbreaks in θ and δ Rhythms as Basic Characteristics of the Micro-Architecture of Sleep and Awakening ”by Jillin W.J. Wang, Fabrizio Lombardi, Xi'an Gian, Crystal Anelet and Plamen Ch. Ivanov, November 14, 2019, PLOS Computational Biology .
doi: 10.1371 / journal.pcbi.1007268