How sleep influences memory (and learning)

Sleep influences learning and memory

In the process of learning, and more precisely, in memory consolidation , sleep plays a significant role. Because during a specific phase of sleep, information is transferred to long-term memory. Finally, one good news in this series of articles, because until now I said only that learning is tedious, learning is a long process, not an event. Learning does not have shortcuts. Here is finally one easy to follow for improving your learning: get enough sleep. Although, for many people, this is also not so easy to do.

“Between 10% to 30% of adults struggle with chronic insomnia” (Source: Sleep Foundation )

In order to understand the importance of sleep, I am going to start with the effects of sleep disorders and insufficient sleep.

What does insufficient sleep mean? How much sleep should we get per night?

A rule of thumb says that we need 7 hours of sleep/night for the best health and wellbeing. In the next chapters, I will explain the sleep cycles and their length so that you can calculate how many hours of sleep you need.

We are getting less and less sleep

Life keeps us busy … even during the night. And that is neither healthy nor appropriate for learning.

• 32.6% of working adults reported sleeping six or fewer hours per night in 2017–2018, up from 28.4% in 2008–2009. (Source: Sleep Foundation)
• Adults are averaging 1 to 2 hours less daily sleep than they did in the mid-20th century. And 39% currently get less than 7 hours of sleep, as compared with 15% in the mid-20th century. (Source: Sleep Foundation)
• No wonder “almost half of all Americans say they feel sleepy during the day between three and seven days per week” (Sleep Foundation)

What is the cost to pay for less sleep? I am glad you asked!

Insomnia and sleep deprivation are correlated with mental health disorders and depression:

- “40% of people with insomnia are believed to also be affected by a mental health disorder.”

- “around 75% of adults with depression suffer from insomnia” (Sleep Foundation)

As sleep deficiency accumulates, the cognitive functions associated with learning : attention ,?memory , and complex decision-making, deteriorate proportionately. One study reported that 36 hours of sleep deprivation resulted in a 40% loss in the ability to form new memories.

“Sleep and learning are strongly linked. Numerous experiments show that spontaneous variations in the depth of sleep correlate with variations in performance on the next day”(Stanislas Dehaene – How we learn)

Let's see why sleep deprivation inhibits memory formation. And what can we do to avoid it?

Sleep architecture

Over the night, we have more sleep cycles. The normal person experiences four to six sleep cycles; the average individual has five of those cycles.?One sleep cycle is something between 90 and 120 minutes.?

One sleep cycle contains more sleep phases. I will discuss them together with the sleep architecture in the next two chapters. First, in a simple way, for a basic level of knowledge. And then with more dedicated terminology for those who want to dive deeper into the sleep ... architecture.

The simple explanation of sleep architecture

One sleep cycle has three phases:

• light sleep,
• deep sleep (both categorized as NREM sleep)
• REM sleep

REM comes from rapid eye movement, and NREM comes from non-rapid eye movement.

The sleep cycles are not identical. The first sleep cycles have more deep sleep phases than light sleep and REM sleep. Because in deep sleep the body repairs itself, at the beginning of the night we have more cycles of sleep dedicated to body restoration than sleep dedicated to the mind. The first hours of sleep are for body restoration. So that the body can function even with less sleep. According to the principle: every body must function, but not everybody must learn. This type of restorative sleep makes up 23% of your sleep and is called "wake up and feel good". It is physical restorative sleep.

The relation between sleep and memory

REM sleep comes from Rapid Eye Movement because we move our eyes during this sleep phase. REM, also known as paradoxical sleep, is a unique phase of sleep in mammals and birds. This sleep makes up 20-25% of total sleep in healthy adults and is mentally restorative; this is why it is associated with memory consolidation.

Newborns spend 50% of their sleep in the REM phase, and they get directly in this phase of sleep, skipping the others. During this phase of sleep, we move information into long-term memory storage. We can say that during this sleep phase, we build memories.

REM sleep is incredibly important, mostly when you want to improve your memory, or when you are learning or attending long trainings. We have longer REM sleep phases at the end of the night, meaning at the end of the sleep cycles. This is why it is important for your memory and learning to sleep long (enough).

A more detailed explanation of sleep architecture

Sleep has 5 phases: wake, N1, N2, N3, and R. But while sleeping, only the last 4 phases are present. One cycle has all four phases, but the duration of those phases is not equal for all cycles.

Phase W

The stage Wake, also known as W is the stage before falling asleep. Particularly important at this stage are more than 50% alpha waves and eye movements.

Phase N1

The next phase is N1, a light phase of sleep, that is more of a transitional phase. It lasts from 1 to 5 minutes, muscle tone is still present, and breathing gets regular.

Phase N2

The N2 is a deeper sleep phase than the one before. In this phase, the heart rate and body temperature drop. The duration of this phase of sleep is 25 minutes in the first cycle, and it lengthens with each successive cycle.

Phase N3

Then it follows the deepest sleep phase: N3. It is hard to wake someone up from this phase of sleep. But if you do, they will have a transient phase of mental fogginess. For about 30 minutes, their mental performance will be impaired. This is the stage of body restoration where the body grows tissues and builds bones and muscles.

Phase R or REM

And finally, the phase that is correlated with building memory is the R or REM phase. The REM starts about 90 minutes after you fall asleep, and in the first cycle it lasts only 10 minutes. It gets longer and longer with the next consecutive cycles, and the last one could last even an hour. In this phase, the muscles are paralyzed, because this is the phase where we have dreams.

If the fact that you paralyze approximately five times each night makes you fearful, wait till you find out what could happen if you didn’t. If muscles were not paralyzed, we would act out of dreams. The REM sleep disorder is exactly the malfunction of this transition into paralysis. This transition is called the switch.

True story related to REM sleep disorder

And here comes a story that is sad and funny at the same time about this REM malfunction that I heard from a sleep doctor. He was talking about one of his patients who suffered from such a disorder; his muscles didn't paralyze in the REM phase. As a consequence, he acted out of his dreams during the night. The guy has decided to finally visit the doctor after once waking up with his arm around his wife's neck.

You must think: why would someone go to a sleep doctor because he wakes up being affective with his wife?

But here are the missing details: the guy was a hunter, and in hunting, there is a rule. If you shoot a deer and it doesn't die, in order to shorten the suffering, you must break its neck (I doubt a bit about this hunting rule, but I pass the information just as I have heard it). Having all details now you might wonder what makes more sense in their case: to go to a doctor or to a lawyer? ;)

Now we can feel lucky for having our muscles paralyzed in REM sleep and not being able to move. There are still two exceptions to paralysis here: the eyes and the diaphragmatic breathing muscles. It kind of makes sense for this one to stay functional so that we can stay alive.

How to ensure more REM sleep

When was the last time somebody told you when to go to sleep?

Now I might remind you of your mother when she kept sending you to bed in your childhood. I take the risk!

The secret to sleeping enough REM phases for memory consolidation is related to when the alarm goes off.?In order to get enough REM sleep turn off the alarm for waking up … and set an alarm for going to bed.

The time to get up is socially determined: work, school, kindergarten, etc. From that moment, count back 90 minutes multiplied by 5 sleep cycles. That is the moment you should set an alarm for going to bed. If you sleep for five cycles, you should be able to wake up without an alarm. But in the beginning, set one just for safety. If you practice this habit, soon you will not need an alarm in the morning anymore.

You might have a sleep cycle longer than 90 minutes. In this case, you have to find out how long your sleep cycle is and redo the calculations to determine the time to go to bed. There are even apps to help you find out how long those are.

I'll end with Bill Clinton's advice to Obama related to the importance of sleep:

"In my long career, most of the mistakes I made, I made when I was too tired... You make better decisions when you are not tired. So that would be my only advice."

Pretty impressive advice when you think of all the things that he could have told him. But no, he told him to sleep.