Why sleep is important for your memory

We sleep for a third of our life. That means if you are 80 you have been asleep for 27 years! But many of us give surprisingly little attention or care to our sleep. We should do however, because it is critical for our memory right now and later in life. 

In the 1950s, we spent, on average, 8 hours a night sleeping. In our modern busy lives, we only sleep for about 6.5 hours. That is 1.5 hours of sleep per night lost in 70 years.

This neglect of our sleep is often the result of a major misunderstanding. Sleep isn’t lost time or a way for us to rest when all of our important work is done. When we fall asleep, our brains are not merely offline, they're busy organizing new memories and integrating them with old ones. While we sleep the memory editor in our brain replays the experiences of that day and stores the highlights in memory.

A good night’s sleep is critical for your memory now and later in your life.  At first glance our memory does not seem that impressive. We normally forget 40% of new material within the first twenty minutes. However, if you sleep well, for 8 to 9 hours a night, it actually helps you stop forgetting and start remembering those important things that you have learned.

There are two basic types of sleep:  rapid eye movement sleep (REM sleep), which is when you dream and non-REM sleep (which has four stages).  You cycle through all stages of non-REM and REM sleep several times during a typical night, with increasingly longer, deeper REM periods occurring towards the morning. 

Whether you are trying to remember factual information or learn a new skill, you form a new memory by engaging with that information. By engaging with the information, the brain forms a representation it. After the memory has first been born, its representation in the brain is very fragile and vulnerable to being deleted or interfered with by competing information. For a memory to persist, it needs to be consolidated: the new memory is solidified into the architecture of the brain, making it less vulnerable to being deleted.   

The sleeping brain provides the perfect conditions for memory consolidation with different kinds of memories being processed during different stages of sleep.

One of the benefits of dreaming in REM sleep is that it connects up the information that we have previously learned with new information we have learned. Each of old and new memories speak to each other. The brain starts to seek out and test novel connections create new associations between these different memories.  You wake up the next morning with a revised memory network in your brain that is now capable of divining incredible solutions to previously impenetrable problems.

Let's say you are learning a new skill, like a karate move or new piano piece. The sequences of kicks and punches or musical scale that you practiced when you were awake are repeatedly rehearsed when you are in REM sleep but, incredibly, at twenty times the speed. The brain compresses time to rehearse your skill memories. The better you rehearse these skill memories during sleep the better your karate move or piano piece becomes. You don’t just learn and hit the save button on these memories. You sculpt them during sleep and improve them. Practice does not make perfect, practice with a good night of sleep is what makes perfect!

A recent discovery is that you also need to sleep not just after learning, but also before learning. This is to prepare your brain, like a dry sponge ready to soak up the new learning.  Without sleep the memory circuits in your brain becomes waterlogged and you can’t absorb new information. In fact, when you are deprived of a night of sleep your brain is 40% worse at making new memories. At school or college, 40% is the difference between an A-grade or completely failing an exam.     

We are now starting to understand what has gone wrong in our brain to produce these sorts of learning deficits. There is a structure in your brain called the hippocampus which is incredibly important for your memory. It is like the inbox of your brain. It is very good at receiving new memory files and storing them. When you are sleep deprived the brain shuts down all the activity in the hippocampus. The brain shuts down your memory inbox and all incoming files are bounced. You can’t commit new experiences to memory. 

If you have seen the film Memento. you get an idea of what is like to not be able to form new memories. In Memento, Guy Peirce has dense amnesia which is caused by severe damage to the hippocampus.  Sleep deprivation attacks and shuts downs the same brain structure which causes dense amnesia!

A physiological signature of ageing is that your deep sleep (stage 4 or slow wave sleep) gets worse. Disruption of deep sleep as we get older might explain why our memory gets worse when we get older.

In fact, sleep deprivation has been strongly linked to development of Alzheimers disease. During deep sleep at night there is a sewage system that goes into overdrive and cleanses the brain of all the metabolic toxins that have been built up over the day. One of these toxic sticky proteins that build up during the day is called beta-amyloid, which is one the leading causes of Alzheimer’s disease. The more sleep you lose across a lifetime the more this toxic amyloid is building up, night after night, year after year – significantly increasing your chances of developing Alzheimer’s!  

Indeed, people who pride themselves on not needing much sleep might actually be increasing their chances of major memory problems later in life. To give you two real examples. Both Ronald Reagan and Margaret Thatcher often claimed they only needed a few hours’ sleep a night. And both sadly developed Alzheimer’s Disease later in life. 

So what can help you get those 8 to 9 hours of sleep a night that you need? Here’s five tips based on the latest sleep science.

  1. Keep your sleep routine regular. The single most important step is to go to bed at the same time, wake up to same time. No matter whether it is the weekend, weekday or holiday.
  2. Keep it dark in your house.  In the last hour before bed try to stay away from screens. Switch off half the lights in the house. It really starts to make you feel a bit more drowsy
  3. Keep it cool – your brain needs to drop its temperature by about 2-3 degrees Fahrenheit to initiate sleep. You will always find it easier to fall asleep in cold room than in a warm room. One way to do this to have a hot bath. Core body temperature plummets when you get out of the bath and helps you get to sleep.
  4. Keep away from physical activity. Don’t Exercise before bed - relax and clear the mind before bedtime; read a book, listen to quiet music.
  5. Keep away from the kitchen. Don't eat a heavy meal or drink an excessive amount of liquid just prior to bedtime.



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