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A group of academics from across the arts and sciences have come up with a theory that may explain the complexity of the brain as well as the importance of sleep. To demonstrate that the brain must periodically reset its operating system, researchers recently recorded the brain activity of sleeping mice for publication in the journal Nature Neuroscience. (Also read | How disrupted sleep causes problems with memory and thinking: Study,
Like food and drink, sleep is also a basic necessity. “You’ll die without it,” warns Keith Hengen, an assistant professor of biology at Washington University in St. Louis.
But what does sleep achieve? For years, academics could only say that sleep reduces fatigue, which is hardly a satisfactory explanation for a basic human need.
“The brain is like a biological computer,” Hengen said. “Memory and experience change the code bit by bit during wakefulness, gradually pulling the larger system away from an ideal state. The central purpose of sleep is to restore an optimal computational state.”
Co-authors of the paper include physics professor Ralf Wessel; Yifan Xu, a graduate student in biology studying neuroscience; and Aidan Schneider, graduate student in the Computational and Systems Biology program, all in Arts & Sciences.
Wessel said that physicists have been thinking about serendipity for more than 30 years, but they never dreamed that this work would affect sleep. In the world of physics, criticality describes a complex system that exists at the tipping point between order and chaos. “At one end, everything is completely routine. At the other end, everything is random,” Wessel said.
Criticality maximizes the encoding and processing of information, making it an attractive candidate for a general theory of neurobiology. In a 2019 study, Hengen and Wessel established that the brain works actively to maintain gravitas.
In the new paper, the team provides the first direct evidence that sleep restores the brain’s computational power. This is a far cry from the long-held belief that sleep must somehow replenish mysterious and unknown chemicals lost during wakefulness.
Following their 2019 paper, Hengen and Wessel theorized that the brain must be seriously diverted from learning, thinking, and wakefulness and that sleep is perfectly suited to resetting the system. “We realized this would be a really good and intuitive explanation for the original purpose of sleep,” Hengen said. “Sleep is a system-level solution to a system-level problem.”
To test their theory on the role of serendipity in sleep, the researchers tracked the spiking of several neurons in the brains of young mice as they went about their normal sleep and wake routines.
“You can follow these tiny steps of activity through neural networks,” Hengen said. These waterfalls, also called neural avalanches, represent how information flows through the brain, he said.
“At severity, avalanches of all sizes and durations can occur. Away from severity, the system becomes biased toward only small avalanches or only large avalanches. It’s like writing a book and being able to use only short or long words. are equal.” As predicted, avalanches of all sizes occurred in rats that had just woken up from restful sleep. During the wake, the waterfalls began to shift towards smaller and smaller sizes.
The researchers found that they could predict when the mice were about to sleep or wake up by tracking the distribution of avalanches. When the size of the cascade reduced to a certain point, sleep was not far off.
“The results show that each waking moment seriously pushes relevant brain circuits away, and sleep helps reset the brain,” Hengen said.
When physicists first developed the concept of gravity in the late 1980s, they were looking at piles of sand on a checkerboard-like grid, a scenario that seemed very far from the mind. But those sand piles provided an important insight, Wessel said.
If thousands of grains are dropped onto a grid following simple rules, the pile quickly reaches a critical state where interesting things start to happen.
Both large and small avalanches can begin without warning, and avalanches from one area begin to spread to other areas. “The whole system organizes itself into extremely complex things,” he said.
Neural avalanches in the brain are like avalanches of sand on a grid, Wessel said. In each case, the cascade is the hallmark of a system that has reached its most complex state.
According to Hengen, each neuron is like an individual grain of sand, following very basic rules. Neurons are essentially on/off switches that decide whether to fire based on direct input.
If billions of neurons can reach serendipity – the sweet spot between too much order and too much chaos – then they can work together to create something complex and wondrous.
Hengen said, “Importance maximizes a set of characteristics that the brain finds very desirable.”
The new study was a multidisciplinary effort. Hengen, Xu, and Schneider designed the experiments and provided the data, while Wessel joined the team to apply the mathematical equations needed to understand sleep in the framework of serendipity. “This is a beautiful collaboration between physics and biology,” Wessel said.
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