Study Provides First Evidence for Why we Sleep

Scientists have integrated physics and biology in a study that offers the initial direct evidence elucidating the purpose of sleep. By likening the brain to a biological computer depleted of resources during wakefulness, they showed that sleep acts as a reset for the brain’s ‘operating system,’ restoring it to an optimal state for enhanced thinking and processing.

For centuries, scientists and researchers have grappled with the inquiry: Why do we sleep? What purpose does satisfying this basic requirement serve? A search for ‘why do we sleep’ on Google yields diverse explanations from different sources. Some contend that sleep eliminates brain toxins, while others argue it aids in bodily repair, rejuvenation, or plays a crucial role in the formation of long-term memories.

A recent investigation conducted by scholars from the University of Washington in St. Louis offers the initial conclusive proof that could address the long-standing question.

Describing the brain as a biological computer, Keith Hengen, the study’s corresponding author, explained, “Memory and experience during waking change the code bit by bit, slowly pulling the larger system away from an ideal state. The primary function of sleep is to restore an optimal computational state.”

A Noteworthy Comparison

Drawing parallels between the brain and a sophisticated computer is not too far-fetched. Both utilize electrical signals for information transmission, likening long-term memory to a hard disk for storage and retrieval, and comparing neurons to circuitry. The use of a computer involves running resource-intensive processes in the background, leading to a gradual slowdown over time. In this study, researchers applied the ‘criticality hypothesis,’ suggesting that the brain operates in a similar manner.

In the realm of physics, criticality refers to a complex system existing at the delicate balance between order and chaos. Physicists introduced this concept in the late 1980s, conducting experiments where they dropped thousands of grains of sand onto a checkerboard-like grid. Eventually, the sand piles reached a point where abrupt, unpredictable avalanches occurred, cascading from one square to others.

Describing the phenomenon, Ralf Wessel, one of the study’s co-authors, stated, “The whole system organizes itself into something extremely complex.”

Applying the criticality hypothesis to the brain, the researchers draw a parallel between each neuron and individual grains of sand adhering to basic rules. Neural avalanches, akin to those created by physicists with sand, signify a system at its most complex state. When neurons reach the optimal balance between order and chaos, known as criticality, the brain’s information processing is maximized.

Insights from Previous Research and Current Sleep Study

In 2019, Hengen and Wessel explored the criticality theory, demonstrating that the brain actively maintains this state. In the current study, they, along with fellow researchers, aimed to understand the role of sleep within the criticality framework. Electrophysiological responses of single neurons in the visual cortices of young rats were measured as they naturally cycled through sleep and wakefulness.

Hengen explained, “At criticality, avalanches of all sizes and durations can occur. Away from criticality, the system becomes biased toward only small avalanches or only large avalanches.”

The researchers observed varied avalanches in rats after restorative sleep, while during wakefulness, the cascades shifted toward smaller sizes. Predicting sleep or wakefulness became possible by tracking the distribution of neural avalanches, with reduced cascade sizes indicating impending sleep.

Hengen concluded, “The results suggest that every waking moment pushes relevant brain circuits away from criticality, and sleep helps the brain reset.” Overall, the researchers propose a model where sleep functions to restore criticality, counteracting its gradual decline during wakefulness. Their findings align with the hypothesis that sleep’s primary regenerative function is the preservation of criticality.

Read the original article on: New Atlas

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