Sleep VI

Matthew Walker finally starts to get into the juicy parts of WHAT is it that sleep actually does for your brain. He starts by telling us about memory and how sleep helps augment that function of the brain. He divides the assistance sleep provides into a couple of sections and Im sharing some notes I made on those sections below. We have established before that all types of sleep - NREM (all stages) and REM sleep responsible for different functions in the body & mind and can therefore not substitute for each other. You can not be missing out on either kind if you wanted to live a more healthy, happy and productive life. 

I am currently learning a new language - French. I am also teaching many back to back yoga classes, the first of which starts at 6:30 am. I need to wake up at 5:30 am to get ready, arrive at a certain balanced frame of mind before teaching my students. Calculating backwards means I need to sleep at 9:30pm to get a full night's beauty sleep. Truth be told, I used to be quite frivolous with the way I treated my sleep - most people do so through their twenties. Matthew's book and a couple of other lifestyle changes made me take stock of how i am sleeping and start to get better at it. Now, I am bringing up these details because learning French is actually putting pressure on me to sleep well and to sleep on time so I get the full eight hours. Because I have read this book I realise the immense contribution of sleep on memory and learning and through experiments on myself I have noticed that on the days I have slept well, I can recall new words and grammar rules I have learnt more or less effortlessly. Now why will i let go of that superpower when all i need to do to retain it is sleep at 9:30PM. For those of you wondering - yes I have sacrificed on my social life! 

Sleeping the night before learning

Like I have in the previous post, I always knew napping in the daytime was a good thing to do! In this book Matthew gives us a 101 reasons to do it more. I need to re-include day time napping in my schedule - somehow! When we are acquiring and absorbing new pieces of information. For fact-based memory - names, telephone numbers etc,  Hippocampus region of the brain is activated, this part of the brain acts as a short-term storage and like all short-term storages, it's capacity is limited. Which means we can run out of storage space ! How does the brain solve this problem. Come on now - i don't need to answer that! "sleep restores the brains capacity for learning, making room for new memories. How though?

This memory refreshment function of the brain is handled by the lighter stage 2 NREM sleep and sleep spindles within that type of sleep. What sleep was doing during these spindles was transferring information from the hippocampus to the more long term storage site of the cortex (this was observed through electrical activity between these two sites). So sleep was clearing out the hippocampus so it could be used for new learning now that all the previously learned information was safely lodged in the cortex. Of course more sleep spindles = greater restorations of overnight learning ability the next morning.

Now the point that made me climb into bed at 9:30pm - the concentration of NREM sleep spindles is rich in the late-morning hours, sandwiched between long periods of REM sleep - by sleeping less than 6 hours - we are denying the brain this learning restoration! 

Sleep the night after learning

The first point was about sleep clearing out space for future learning. The section is about how sleep makes sure that what is learnt is stored safely - memory consolidation. The book mentions two researchers, John Jenkins and Karl Dallenbach, who found that time spent asleep help cement the newly learned chunks of information, preventing them from fading away - that same time spent awake would lead to a dangerous forgetting ! How much you say - about 20-40% memory retention benefit is accrued by sleep. 

REM sleep and lighter NREM sleep happens late in the night and NREM sleep is earlier in the night. When researchers limited participants to sleeping only first half OR second half of the night - they found that "the early-night NREM rich deep sleep was what was providing superior memory retention savings relative to late-night, REM-rich sleep"

In other experiments, when comparing where participants were accessing newly learned information from in their brains, it was found that before sleeping they were recalling information from a vulnerable short-term hippocampus storage site and after sleep  they were accessing the same information from the more durable long term storage site - the neocortex, sitting on top of the brain. The book shares that day-time naps (even a 20-mins tiny one) offer memory consolidation as long as they obtain enough NREM sleep. 

"Sleep is modifying the information architecture of the brain at night"

Something else that is super interesting is that post sleep you can suddenly remember pieces of information that you were not being able to recall before. 

Sleeping to forget

So we sleep to remember and get better at learning. What about the opposite - does the sleep help in deleting  pieces of information that are no longer required of serve any purpose in our lives? Looks like it does! In an experiment, researchers showed participants two sets of cards - one was tagged for forgetting and one was tagged for remembering. The participants who slept post this exercise were able to distinguish between the two sets of information and they were selectively recalling only  those that were tagged for remembering, those who did not sleep showed no such differentiation in the saving of memories.  

As I was reading this book, my face would resemble the emoji that was registering awe & shock (😮). At the above piece of information my face was that emoji many times multiplied. Sleep was so smart! As Matthew Walker says "Sleep is able to offer a far more discerning hand in memory improvement:one that preferentially picks and chooses what information is and is not, ultimately strengthened."

They found NREM sleep responsible for this amazing feat of distinguishing between memories we needed to remember and stuff we needed to forget. 

Sleep for other kinds of memories

We have spoken about fact-based memories, there is another kind - skill memory like riding a bicycle, cooking, baking, even yoga ! The brain remembers the routine of executing a particular skill. Matthew in fact speak about how when learning a new skill, it is not just practice that makes perfect, it is practice with sleep that really cements that learning. In an experiment he conducted he found that when teaching participants a new motor skill, those who were tested after a night's sleep performed better (20% jump in performance) and a 35% jump in accuracy as compared to those who hadn't slept. What was more interesting is that when these sleep deprived individuals were given the chance to rest and catch up on sleep, they too caught up in performance and accuracy - so the brain continues to work on skill memories in the absence of practice - it is practice followed by a night of sleep that leads to perfection ! 

The increases in speed and accuracy of certain other experiments were due to stage 2 NREM sleep especially in the last two hours of an eight hour sleep - again the sleep spindles were to be credited for this beautiful feat, they were responsible for the offline memory boost. As if this was not magical enough, the researchers discovered that these sleep spindles were concentrated on the region responsible for that particular motor skill. Although they bathed all parts of the brain, they paid special attention to the part that had done the motor skill learning during the day. 

Sadly, this last two hours of sleep is exactly what we sacrifice in our busy weekday lives and therefore miss on these gorgeous sleep spindles. Day time naps are also believed to contain many sleep spindles that are helpful for motor-skill memory improvement, additionally they also repair and restore the muscles and replenish depleted energy stores.

When I was working with athletes in France, i realised how hard they worked at their sport - rowing. They not only rowed for many many hours during the day but also cycled and trained during other parts of the day/week. Most of them slept well, but some of them did not - and they often gave up on the early morning sleep-spindles rich sleep. Mathew Walker in the book mentions why it is especially important for athletes to get a full eight hour sleep:

• reduced time to physical exhaustion
• improved aerobic output
• better limb force extension and vertical jump height
• better sustained muscle strength.
• Better cardiovascular, metabolic and respiratory capabilities. 
• Body betters itself at cooling itself down through sweating
• Decreases in lactic acid build up, blood oxygen saturation and carbon dioxide build up.
• Lesser injury risk

Sleeping before a game is important but so is sleeping after a game! Post performance sleep accelerates physical recovery fro common inflammation, stimulates muscle repair and helps restock cellular energy in the form of glucose and glycogen.

Is this not enough evidence for why we SHOULD be sleeping a full 8 hours and especially not skip the early morning light NREM sleep that help us refine and retain motor movements. This is especially important in the early years of human life, which is why we see a spike in the stage 2 NREM sleep and sleep spindles during the infant's time of transition from crawling to walking.

Sleep and creativity

The last section is also something very important for me personally. With all this information that the brain has, it can either retain them in isolation or it can try and do something magical ~ and we know that sleep is nothing but a magician. The REM dreaming state of sleep is credited with making connections within all of the information the brain retains thereby aiding us in problem solving as well as creativity. The sleeping brain fuses together disparate sets of knowledge that foster impressive problem-solving abilities. 

These were my notes from this chapter - if you think this was mind-blowing wait for what the next chapters have in store!