(Credit: Andrea Piacquadio from Pexels)
ST. LOUIS —Â What is the purpose of sleeping? Researchers at Washington University in St. Louis believe they have unraveled the mystery, proposing that sleeping acts as a reset button for the brain’s “operating system.” This novel theory, integrating concepts from physics and biology, suggests that sleep is essential for maintaining the brain’s optimal state for processing and thinking.
“The brain is like a biological computer,” says study author Keith Hengen, an assistant professor of biology at Washington University in St. Louis, in a university release. “Memory and experience during waking change the code bit by bit, slowly pulling the larger system away from an ideal state. The central purpose of sleep is to restore an optimal computational state.”
This study closely observed the brain activity of sleeping rats to support this hypothesis. The theory hinges on a concept known as “criticality,” a state that balances order and chaos, maximizing information processing. Criticality, a term from physics, describes a complex system at the tipping point between complete regularity and randomness.
“At one extreme, everything is completely regular. At the other extreme, everything is random,” notes study co-author Ralf Wessel, a professor of physics at Washington University in St. Louis.
Researchers observed the brain activity of young rats during sleep and wakefulness. They tracked neural avalanches — cascades of brain activity — which demonstrated how information flows through the brain. They found that after restorative sleep, the brain exhibited avalanches of all sizes, indicating a return to criticality. As the rats stayed awake, these cascades shifted towards smaller sizes.
The study marks a departure from the long-held belief that sleep replenishes depleted chemicals. Instead, it posits that sleep is a systemic solution to a systemic problem, resetting the brain away from the extremes of too much order (rigidity) or chaos (randomness).
The concept of criticality was first developed in the late 1980s by physicists studying sand piles on a grid. These sand piles self-organized into a complex system, a metaphor for the neural avalanches in the brain. Hengen notes that every neuron, like an individual grain of sand, follows basic rules. When billions of neurons reach criticality, they create a complex and efficient system.
“Criticality maximizes a bunch of features that sound very desirable for a brain,” explains Hengen.
This multidisciplinary effort combines experimental data from biology with mathematical equations from physics, providing a novel perspective on the purpose of sleep.
“It’s a beautiful collaboration between physics and biology,” says Wessel, highlighting the unique blend of disciplines that led to this discovery.
The study is published in the journal Nature Neuroscience.
