Sleep III
I took a break from writing the articles on sleep. I finished reading the book, and I am currently on a quest to re-read it, so that the message it imparts stays firmly lodged in my mind. Sometime I think re-reading books is one of those luxuriously wasteful things to do - because there are so many books to read in the world. But once a while, you do come across masterpieces that need to be read again - lest you have forgotten what it taught you. Why We Sleep happens to belong to the latter category.
Matthew Walker starts off by telling us about the signs of sleep. There are two:
This does not mean that your eyes, ears and noise have suddenly lost their ability to function. They continue doing their work - but the signals from the sensory organs do not reach the brain. What stops it? A barricade called Thalamus, a small oval shaped object that is located in the brain.
Source : Pearson Education
Thalamus acts as a gate that lets the sensory inputs through to the cortex to the top of the brain where they are interpreted. During sleep Thalamus shuts off this gate and hence you are no longer aware of what's happening outside even though your sensory gates pick up signals throughout the duration of your sleep.
Time distortion
You lose a sense of time when you sleep. It happens often to me - I wake up at 6:00am and then tell myself 6:15am because event he fifteen minutes of extra sleep feels like an entire hour of rest! however while your conscious mapping of time is disrupted when you're sleeping, the brain keeps logging time non-consciously. Matthew Walker gives a brilliant example which is definitely true for me. When I know I have an early flight to catch the next day, i always wake up 5 or 10 minutes before the alarm rings. I often pat my intelligent brain for inherently knowing what time it is.
Last thing mentioned about time distortion is time dilation in dreams. Which is when time moves very slowly in our dreams as compared to reality - time is hence stretched. During an experiment on rats, researchers found that during REM sleep (which I shall come to in a bit), the activities of the day were being replayed in the brain, and being replayed very very slowly - at half or quarter the speed of the actual event.
These including some other signs which include the fact that sleep is reversible (vs a coma is not) and has a reliable pattern establish the fact that a person is asleep. Scientifically, there are three things researches measure to ascertain that an individual is asleep:
Brainwave activity
Eye movements
Muscle activity
Matthew mentions a breakthrough research made by two scientists : Eugene Aserinsky and Professor Nathaniel Kleitman. Observing infants they noticed that there were periods of sleep when the eyes moved rapidly from side to side and these sleep phases were accompanied by frantic brain activity as well. And then there were other periods when the eyes would remain calm - which then matched with slower brain waves as well.
Now, why is sleep structured like this? Why can't we get all of our NREM sleep and then dive into REM ? Or why isn't it structured a little bit more rationally with similar proportions throughout the night?
Throughout the book Matthew Walker talks about nature as Mother Nature - i love it when he says that- it appeals to the side of me that believes that everything in this life and in fact all of our lives are made with love by this divine feminine spirit/energy - Shakti. Before I take off on my tangent of the feminine divine, I'll pull myself back to the topic of Sleep.
Mother nature, Matthew says is intelligent enough to have done this split across the night the way she has done it. We will get into details of the functions of the two types of sleep in future posts. For now, all we need to know is that NREM does the much required job of clearing out our short-term memory storage of all the information it has acquired in the day - memories that are unimportant, duplicated are thrown out and memories that are important and will be of use in the future are transferred to the longterm storage hold. What this does is then clears out the limited space we have in the short term storage.REM in contrast utilizes those memories to make connections with previously stored information. So for REM to do it's job, NREM need to work first.
But why the switch between NREM and REM constantly in the night? Because NREM can't get all of the job done in one go. It takes a first stab, REM jumps in and uses whatever has been transferred to form connection and enhance certain features of those memories to make them useful for us - in case we call upon it in the future. NRE< then jumps back in and does a second round of cleaning followed by REM for more fine-tuning. And this process goes on until the last few hours of the night when NREM's job is more or less done and REM can then utilise sleep as it's playground to do everything it needs to do.
Because we make fresh memories everyday - this process needs to be repeated every night for our brain to function efficiently and for us to make sense of the world, our emotions, the skills we have learnt etc. Now you realise the importance of the full 8 hours of sleep - because missing out on any part of the sleep means you miss out the particular function of NREM and REM and hence miss out on either the cleaning up or the refining processes - both of which will limit the way you live and make sense of your life
Source : bama.ua.edu
The chart above shows us the brainwaves associated with different stages of sleep. Some keys points that follow from the above chart are:
Matthew Walker starts off by telling us about the signs of sleep. There are two:
- Absence of awareness of your external surroundings.
- Distortion of time
Absence of awareness
Source : Pearson Education
Thalamus acts as a gate that lets the sensory inputs through to the cortex to the top of the brain where they are interpreted. During sleep Thalamus shuts off this gate and hence you are no longer aware of what's happening outside even though your sensory gates pick up signals throughout the duration of your sleep.
Time distortion
You lose a sense of time when you sleep. It happens often to me - I wake up at 6:00am and then tell myself 6:15am because event he fifteen minutes of extra sleep feels like an entire hour of rest! however while your conscious mapping of time is disrupted when you're sleeping, the brain keeps logging time non-consciously. Matthew Walker gives a brilliant example which is definitely true for me. When I know I have an early flight to catch the next day, i always wake up 5 or 10 minutes before the alarm rings. I often pat my intelligent brain for inherently knowing what time it is.
Last thing mentioned about time distortion is time dilation in dreams. Which is when time moves very slowly in our dreams as compared to reality - time is hence stretched. During an experiment on rats, researchers found that during REM sleep (which I shall come to in a bit), the activities of the day were being replayed in the brain, and being replayed very very slowly - at half or quarter the speed of the actual event.
These including some other signs which include the fact that sleep is reversible (vs a coma is not) and has a reliable pattern establish the fact that a person is asleep. Scientifically, there are three things researches measure to ascertain that an individual is asleep:
On the basis of this they have classified sleep into two kinds :
- Non-Rapid Eye Movement (NREM) : where the brain activity slows down immensely. NREM can further be divided into 4 stages : NREM 1,2,3,4. Stages 3 and 4 being the deepest NREM sleep which means it is very difficult to wake people up from those phases of sleep.
- Rapid Eye Movement (REM) : where the brain activity resembles an awake state. Also associated with dreaming.
How do we know how these phases of sleep operate and which one comes when? It has been recorded through various experiments that NREM and REM alternate every 90 minutes starting with NREM first as we head to sleep. Here's a hypnogram, that charts the stages of sleep with the duration of sleep.
Source: Researchgate
Matthew Walker adds further information to the above graph saying while "it is true that NREM and REM alternate throughout the night, the ratio of NREM sleep to REM sleep in that 90 minute cycle changes dramatically across the night.
In the first half of the night, the vast majority of our 90 minute cycles are consumed by deep NREM and very little REM. But as we transition through into the second half of the night, most of the time is dominated by REM sleep with very little NREM sleep.
Source: Researchgate
Matthew Walker adds further information to the above graph saying while "it is true that NREM and REM alternate throughout the night, the ratio of NREM sleep to REM sleep in that 90 minute cycle changes dramatically across the night.
In the first half of the night, the vast majority of our 90 minute cycles are consumed by deep NREM and very little REM. But as we transition through into the second half of the night, most of the time is dominated by REM sleep with very little NREM sleep.
Now, why is sleep structured like this? Why can't we get all of our NREM sleep and then dive into REM ? Or why isn't it structured a little bit more rationally with similar proportions throughout the night?
Throughout the book Matthew Walker talks about nature as Mother Nature - i love it when he says that- it appeals to the side of me that believes that everything in this life and in fact all of our lives are made with love by this divine feminine spirit/energy - Shakti. Before I take off on my tangent of the feminine divine, I'll pull myself back to the topic of Sleep.
Mother nature, Matthew says is intelligent enough to have done this split across the night the way she has done it. We will get into details of the functions of the two types of sleep in future posts. For now, all we need to know is that NREM does the much required job of clearing out our short-term memory storage of all the information it has acquired in the day - memories that are unimportant, duplicated are thrown out and memories that are important and will be of use in the future are transferred to the longterm storage hold. What this does is then clears out the limited space we have in the short term storage.REM in contrast utilizes those memories to make connections with previously stored information. So for REM to do it's job, NREM need to work first.
But why the switch between NREM and REM constantly in the night? Because NREM can't get all of the job done in one go. It takes a first stab, REM jumps in and uses whatever has been transferred to form connection and enhance certain features of those memories to make them useful for us - in case we call upon it in the future. NRE< then jumps back in and does a second round of cleaning followed by REM for more fine-tuning. And this process goes on until the last few hours of the night when NREM's job is more or less done and REM can then utilise sleep as it's playground to do everything it needs to do.
Because we make fresh memories everyday - this process needs to be repeated every night for our brain to function efficiently and for us to make sense of the world, our emotions, the skills we have learnt etc. Now you realise the importance of the full 8 hours of sleep - because missing out on any part of the sleep means you miss out the particular function of NREM and REM and hence miss out on either the cleaning up or the refining processes - both of which will limit the way you live and make sense of your life
Source : bama.ua.edu
The chart above shows us the brainwaves associated with different stages of sleep. Some keys points that follow from the above chart are:
- Brainwaves associated with Awake and REM sleep are similar - : Your waking brain activity is frenetic- fast frequency and very asynchronous.
- NREM sleep in contrast has slower waves associated with it and the tempo is decelerated. NREM stage 2 has something called a SLEEP SPINDLE. Remember this because we are going to return to it a lot in future posts. Sleep spindles are like a "new sound overlaid on top of the slow-wave rhythm". Matthew describes it as a "punchy burst of brain wave activity that often festoons that tail end of each individual slow wave". One of their many functions it to protect the daintiness of sleep from any external sounds.
- Most of our brainwaves travel in one direction from front to back. Our deep sleep waves are generated from the center of our forehead - the place where Hindu women wear their bindis.
- Deep sleep is hardly anything but lazy - there are very intricate neural connections and collaboration going on while you are lying asleep.
In this last section, we discuss what happens when these electrical signals flood our brain every night. We spoke about how the Thalamus blocks out any sensory perceptions reaching the cortex when we are asleep. This enables the cortex to slip into it's default mode of deep slow-wave sleep. It is a highly synchronous state of being, very active and according to Matthew also differs from the brain activity of waking meditative states.
NREM sleep because it is characterized by slow-waves enables a certain kind of long range communication within the brain region. What does this communication do? Below are three points to explain it across the three states of waking, deep slow-wave sleep (NREM) and fast-wave sleep (REM):
AWAKE - Reception : this is when we receive all kinds of inputs through our interaction with the world around us. The sensory gates are open and we are seeing, listening, tasting, feeling etc.
NREM - Reflection : Because of it's slow wave, NREM sleep waves can help carry information from the periphery of our brain to the deepest and farthest corners. It acts as a courier that aids in the file transfers of whatever has happened in the day for further processing by the next stage of sleep.
REM - Integration : REM sleep has been called paradoxical sleep, because research has found that certain parts of our brain are more awake in REM than when we are awake! REM, characterized by the faster frequency brainwaves. The sensory gate of the thalamus is again open during REM. This time the inputs are not coming from outside but Matthew says, "signals of emotions, motivations and memories are all played out in the sensory cortices of our brain." What REM is doing is integrating all of that into coherent stories that makes sense to you and makes it easier for your brain to categorise and stores different kinds of information for future recall.
Lastly, if REM and Awake states are so similar how do we know the difference between being asleep and being awake? Mother nature, thankfully, has blessed REM sleep, also knows as the dream sleep, with muscle atonia. Which means that your voluntary muscles go limp and do not respond to commands when you are in REM sleep. Rightly so, because imagine if we were trying to play out everything we were dreaming about physically using out bodies - not exactly helpful
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