The brain reorganizes and recharges itself during sleep.
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Most of us have trouble thinking clearly after a bad night’s sleep—with a foggy mind and an inability to function as usual at school, college, or work.

You may notice that you do not concentrate well, or that your memory is not on point. Regardless, decades of poor sleep can potentially produce cognitive decline.

Bad sleep also affects the mood and behavior of people, whether they are children or adults. So how much sleep does our brain need in order to function properly in the long run? Our new research, published in Nature Aging, offers an answer.

Sleep is an important component in maintaining normal brain function. The brain reorganizes and recharges itself during sleep. In addition to removing toxic waste and strengthening our immune system, sleep is also key to “memory consolidation”during which new memory segments based on our experiences are transferred to our long-term memory.

An optimal quantity and quality of sleep allows us to have more energy and better well-being. It enables the development of our creativity and thought.

Researchers looking at infants between 3 and 12 months noted that better sleep is associated with better behavioral outcomes in the first year of life, such as the ability to adapt to new situations or efficient emotion regulation.

There are important fundamental foundations for knowledge, including the “cognitive flexibility” (which allows us to change our perspective easily), and that they are linked to well-being later in life.

Sleep regularity seems to be connected to the “default neural network” (NDN), which involves regions that are active when we’re awake but not doing a specific task, such as when we rest while our mind wanders.

This network includes regions that are important for cognitive function, such as the posterior cingulate cortex (which is deactivated during cognitive functions), the parietal lobes (which process sensory information), and the frontal cortex (involved in planning and complex cognition). .

The brain reorganizes and recharges itself during sleep.

There are signs that, in adolescents and young adults, poor sleep may be associated with connectivity changes within this network. This is important because our brains are still developing well into our teens and early adulthood.

Disruption of this network may then have a collateral effect on cognition, such as interference with concentration and memory-based processing, as well as more advanced cognitive processes.

Altered sleep patterns, including difficulty falling and staying asleep, are significant features of the aging process. These sleep disturbances are highly likely candidates for being contributors to cognitive decline and psychiatric disorders in older people.

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Seven hours, but no more and no less

We all react differently to lack of sleep.
We all react differently to lack of sleep.

The goal of our study is to better understand the link between sleep, cognition, and well-being.

We found that both insufficient and excessive sleep contributed to poor cognitive function in a middle-aged to older population of 500,000 adults taken from the UK BioBank.

However, we did not study children or adolescents, and as their brains are still developing, they may require different optimal sleep durations.

One of our key discoveries was that seven hours of sleep each night was optimalwith more or less than that providing less benefits in cognition and mental health.

In fact, we found that people who slept that much did, on average, do better on cognitive tests (including processing speed, visual attention, and memory) than those who slept more or less. Individuals also consistently need seven hours of sleep, without much fluctuation in duration.

Said that, we all respond slightly differently to lack of sleep. We found that the relationship between sleep duration, cognition and mental health was mediated by genetics and brain structure.

We found that the brain regions most affected by sleep deprivation included the hippocampus, well known for its role in learning and memory, and regions of the frontal cortex, involved in vertical control of emotion.

Sleep deprivation can affect learning and memory.
Sleep deprivation can affect learning and memory.

But while sleep deprivation can affect our brains, it can also happen the other way around.

It’s possible that age-associated shrinkage of brain regions involved in regulating sleep and wakefulness contributes to sleep problems later in life. It can, for example, reduce the production and secretion of melatonin, a hormone that helps control the sleep cycle, in older adults.

This finding appears to support other evidence suggesting a link between sleep duration and the risk of developing Alzheimer’s disease and dementia.

While seven hours of sleep is optimal for protecting against dementia, our study indicates that getting enough sleep can also help alleviate dementia symptoms by protecting memory.

This highlights the importance of monitoring sleep in older patients with psychiatric disorders and dementia in order to improve their cognitive functions, mental health and well-being.

How to improve our sleep

A good start is to make sure that the temperature and ventilation in our bedrooms are good – they should be cool and airy.

You might also want to avoid drinking a lot of alcohol and not watching scary movies or other scary content before you go to bed. Ideally, you should be in a calm and relaxed state when trying to enter sleep. Thinking about something nice and relaxing, like the last time you were at the beach, works for many.

Think of a nice time you had to relax and be able to sleep.
Think of a nice time you had to relax and be able to sleep.

Technological solutions such as apps or personal devices can also benefit mental health, as well as recording sleep and ensuring consistency of sleep duration.

To enjoy life and function optimally in daily life, you might then monitor your own sleep patterns to make sure you’re getting seven hours of sleep on a regular basis.

*Barbara Jacquelyn Sahakian is Professor of Clinical Neuropsychology and Christelle Langley is Postdoctoral Research Associate in Cognitive Neuroscience, both at the University of Cambridge; Jianfeng Feng is Professor of Science and Technology for Brain-Inspired Intelligence and Wei Cheng is Principal Young Investigator of Neuroscience, both at Fudan University. His original article was published in The Conversation, whose English version you can read .

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