Key points:
- By tracking brain activity in rats, researchers show that the brain needs sleep to regularly reset its operating system to reach “criticality”—a state that optimizes thinking and processing.
- Researchers tracked the distribution of neural cascades, called avalanches, to predict when rats were about to go to sleep or wake up.
- Every waking moment pushes relevant brain circuits away from criticality, while sleep helps the brain reset to maximize these neural functions.
A new study, published in Nature Neuroscience, helps elucidate the purpose of sleep. By tracking brain activity in sleeping rats, researchers show that the brain needs to regularly reset its operating system to reach “criticality”—a state that optimizes thinking and processing.
In the study, researchers provide the first direct evidence that sleep restores the computation power of the brain. This finding is a major shift from the long-held theory that sleep replenishes mysterious and unknown chemicals depleted during wakefulness.
Researchers designed their experiments to test the idea that learning, thinking, and being awake pushes the brain away from criticality, while sleep resets the system. To do so, they tracked the spiking of neurons in the brains of young rats during their normal sleeping and waking routines.
They followed cascades, called neural avalanches, through the neural network to trace the flow of information in the brain. At criticality or after restorative sleep, avalanches of all sizes and durations occur, but as the system moves away from criticality, only small avalanches occur. As a result, the researchers could track the distribution of avalanches to predict when rats were about to go to sleep or wake up.
“The results suggest that every waking moment pushes relevant brain circuits away from criticality, and sleep helps the brain reset,” said study author Keith Hengen, professor at Washington University in St. Louis.
This study provides important support for sleep underlying criticality and points to the possibility of billions of neurons working together to form something complex and wondrous.
“Criticality maximizes a bunch of features that sound very desirable for a brain,” said Hengen.