What do we know about sleep?

Sleep deprivation prevents fixation of memories, cleansing of the brain, and accelerates cognitive decline.

A 1995 sleep experiment, placed two hundred rats on conveyor belts. Belts ran when the rats got sleepy. At the end of the belt was a bucket full of water. As much as 99% of the rats’ sleep was denied. A few days in, rats started eating compulsively while losing weight. Their metabolic rate skyrocketed 200% and skin ulcers appeared. Their blood had abnormal levels of neurotransmitters and hormones, such as norepinephrine and thyroxine. Within two to three weeks, they all died. The research was extreme, yes, but this showed that severe sleep deprivation can have detrimental effects on animals.

Sleep is fundamental

The team at Drowzee has published a series of articles with the latest in science about sleep. One of the scientific truths is the universal need for sleep among most animal species. Entering a state of unconsciousness, exposed to the dangers of the night, doesn’t seem a good idea for survival. From an evolutionary point of view, sleep must facilitate essential functions that outweigh the dangers and lusts of the world.

There are a few species that are capable of falling half-asleep, such as dolphins. They relax one hemisphere of the brain, closing the same side-eye, while the other remains awake. Other species, like pelagic frigates, are capable of staying aloft for weeks by power napping mid-flight. However, most animal species tend to rely on a certain number of hours regularly to maintain stable function.

“Evolutionarily, it seems that sleep is very well preserved, which implies a basic function essential for life”

– Nick Franks, Professor at Imperial College London

With humans, you cannot do experiments as extreme as the one that begins this article. Even on animals, they cannot and shouldn’t be conducted. While ethical standards were less vigilant back then, the study provided some insight into the negative impact of sleep deprivation. These consequences range from harming the body, cognitive abilities, behaviors, and movement.

Known consequences of sleep deprivation

For example, studies on rats have shown sleep deprivation to cause an inability to remember locations. Particularly of where they had found food a few hours earlier. Reaction time at the wheel was found to be severely impaired in a study on humans last year. It was slower for sleep-deprived than for those who exceeded the permitted levels of alcohol. Some months ago, a correlational study revealed a higher incidence of dementia at retirement. This was among 8,000 British officials. Those who acknowledged having slept six or fewer hours in the past decades had a higher prevalence. Last week, at the Massachusetts Institute of Technology, they found students who slept the least were the slowest on a treadmill. Additionally, there are studies with rodents that have shown that leaving them without sleep weakens their immune system.

Imperial College London professor, Nick Franks, points out that the need for sleep must have a very strong biological basis. “Evolutionarily, it seems that sleep is very well preserved, which implies a basic function essential for life. So when we are sleep-deprived, all kinds of things related to our health and behavior go wrong. What is the basic mechanism that tracks how tired the brain is and when to activate sleep remains a great mystery,” he says.

The sleep knowledge paradox

Interestingly, we know more about how bad it is not to sleep than how good it is to do so. It’s one of the paradoxes of sleep science: the evidence for the negative consequences of sleep deprivation is well documented. However, there are more hypotheses than evidence about the benefits of a good night’s sleep. The simplest and most common answer is that the brain needs to rest after receiving a certain amount of stimuli. The problem with this analogy is that brain activity doesn’t stop while sleeping, it just changes.

“The brain rehearses during sleep what happened during wakefulness. We believe that this reactivation process allows the gradual reinforcement of memories over time.”

– Gabrielle Girardeau, Sleep researcher at the Institut Fer à Moulin (Paris, France)

Benefits of sleeping well

In humans, we know that lack of sleep is detrimental to memories. In animals, deprivation also affects memory consolidation. Knowing the negative effects of not sleeping, the positives of doing so must be underpinned.

The hippocampus is a crucial structure for the memory of contextualized events (what, where, when it happened). This structure reactivates waking neural patterns during sleep, in short, coordinated events called ripples. These ripples were tampered with in rats so they would not remember the location of food, mentioned previously. “These waves help to strengthen the memory band and also allow the hippocampus to communicate with other parts of the brain, such as the cortex or the amygdala, to associate, for example, an emotional valence to a memory or to transfer its details to the memory cortex for long-term storage”, he details. And all this cannot be done if you are awake and stimuli from outside do not stop arriving.

Consolidation of memories is not the only mission of “dreaming”, although perhaps the best demonstrated. Laura D. Lewis specializes in neuroimaging at the Department of Biomedical Engineering at Boston University (USA). “The neuroscience of sleep has shown that there is no single reason we sleep: sleep has incredibly wide effects on the brain, affecting everything from molecular processes to high-level cognition,” she says.

“Rodent studies have shown that a variety of metabolites are shed during sleep. This is the case of beta-amyloid, which if it accumulates and is added, appears related to Alzheimer’s disease.”

– Laura D. Lewis, Neuroscientist at Boston University (United States)

Brain health

Lewis’s work is showing that one of the functions of sleep is to remove garbage from the brain. “Many of these metabolites are generated by neurons during wakefulness when they produce various types of molecules naturally while consuming energy and performing their normal functions. This is the case of beta-amyloid, which, if it accumulates and is added, appears to be related to Alzheimer’s disease”, she adds.

They have observed a dual process during sleep. Neurons produce fewer waste compounds, while cerebrospinal fluid and interstitial fluid evacuate existing waste. Similar to more familiar systems. For example, cleaning an office building at night when workers aren’t present. From this perspective, sleep maintains neuronal physiological health.

What’s up, insomnia?

When sleep has so many benefits, why do you sleep so little and badly? Heather Schofield investigates the social dimensions of sleep. She is the Co-founder of the Behavior Development Laboratory at Medina College (University of Pennsylvania, US). “Most laboratory studies have shown the positive effects of sleep,” she says. Although, in her contribution to the Science special, she emphasizes that individuals may prefer to sleep less. This might be due to work or personal needs. “Some people may decide that it is worth compromising and getting less sleep than is recommended by experts.

What are the main drivers in choosing to sleep less? Can it be because we value our present awake time more than our long-term longevity? Or is it simply due to a lack of good solutions to help us sleep better?

#sleep

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