by Researchers have long pondered the purpose of sleep, a fundamental need for all living organisms. While it has been known that sleep reduces sleepiness, this explanation hardly does justice to the importance of sleep. However, a team of researchers from Washington University in St. Louis has proposed a new theory that sheds light on the true purpose of sleep and its role in optimizing brain function. By merging concepts from physics and biology, the team tracked the brain activity of sleeping rats and concluded that the brain needs to regularly reset its operating system to achieve a state of criticality, which enhances thinking and processing.
According to Keith Hengen, an assistant professor of biology at Washington University, the brain can be likened to a biological computer. The code of the brain is continuously altered by memory and experience during waking hours, gradually moving it away from its ideal state. Sleep serves the central purpose of restoring the brain to an optimal computational state. The concept of criticality, a state that exists at the tipping point between order and chaos, holds the key to understanding the brain’s need for regular reset. Criticality maximizes the encoding and processing of information, making it a compelling principle of neurobiology.
The team’s previous research in 2019 already indicated that the brain actively maintains criticality. However, their latest study provides the first direct evidence that sleep is instrumental in restoring the brain’s computational power. This finding challenges the long-held belief that sleep primarily replenishes unknown chemicals depleted during waking hours. Hengen and his colleague Ralf Wessel, a professor of physics, theorized that learning, thinking, and wakefulness push the brain away from criticality, making sleep an opportune time to reset the system.
To test their theory, the researchers monitored the brain activity of young rats during their sleep and wake cycles. They found that neural avalanches, cascades of activity that reflect information flow in the brain, occur at criticality. As the rats wake up from restorative sleep, avalanches of all sizes are observed. However, as waking hours progress, these avalanches shift towards smaller sizes. The distribution of avalanches can be used to predict when rats are about to sleep or wake up, suggesting that wakefulness pushes relevant brain circuits away from criticality, while sleep allows the brain to reset.
The concept of criticality initially emerged in the field of physics, where it was applied to systems such as piles of sand on a grid. These sand piles reach a critical state where interesting phenomena occur, akin to the complex state that occurs in the brain. Wessel explains that neural avalanches in the brain resemble the avalanches of sand on a grid, signifying that the system has reached its most complex state.
Each neuron in the brain acts as an individual grain of sand, following basic rules and firing based on simple inputs. When billions of neurons reach criticality, they work together to create complexity and facilitate optimal brain function. The multidisciplinary nature of this study, with collaboration between the fields of physics and biology, highlights the beauty of this research.
This new theory not only provides a compelling explanation for the purpose of sleep but also demonstrates the intricate relationship between physics and biology in understanding brain function. By elucidating the role of criticality in sleep and brain optimization, this research opens up new avenues for further exploration into the mysteries of sleep and the brain
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1. Source: Coherent Market Insights, Public sources, Desk research
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