Why we sleep?
Assuming we sleep 8 hr/day, on an average, we cover about 1/3rd of our life in sleep. Given the current lock down situation, the number of hours might actually increase. So, have you ever thought “What are you doing in that 33% of your life time and how it is affecting the rest 67%?” which can be rephrased as “Why we sleep?”
This book “Why we sleep — The New Science of Sleep and Dreams” by Matthew Walker, a sleep researcher, professor at UC Berkeley offers excellent advice and debunks many concepts on sleep, dream and has been recommended by Bill Gates as well. Before debunking some myths and common questions, it is important to understand few concepts related to sleep research.
Factors causing sleep
1. Circadian Rhythm or Biological clock
It is an internal process that regulates sleep-wake cycle and gets repeated for every 24 hrs. Simply it can be thought of as an “internal clock” that controls what we should do at particular time. Just like our normal wall clocks can be altered by batteries/manually, this internal clock can be reset by several factors, the most important one being “Daylight”
2. Sleep Pressure
From the moment we are awake, “adenosine” levels increases and accumulates. The more adenosine present in our body, the more we feel to go to sleep. A rough analogy for better understanding is:
Adenosine → Water
Our brain → Dam
Holding adenosine → Dam gates closed, accumulation of water
The act of sleep → Lifting up the dam gates, water drains
The dam can hold the water till a particular point, after which it breaks. In the same way, our brain can hold adenosine accumulation till a value (maybe 12–16 hrs), by that time, we should sleep (i.e lift the dam gates).
Melatonin (Hormone of darkness) which is produced by effect of circadian rhythm gives signal to brain indicating that “It’s time to sleep” thus having influence on when to sleep along with “adenosine” (produced due to sleep pressure)
Architecture of sleep
Sleep cycles
Our sleep consists of regular, non symmetric but repeating cycles (Sleep cycles — each cycle appx lasts for 90 min) which are composed of REM (Rapid Eye Movement) and NREM (Non Rapid Eye Movement) phases that can be characterized by the motion of our eyeballs under the eyelids i.e in NREM eyeballs won’t move and in REM they move rapidly.
NREM Sleep (Deep sleep)
- Has 4 stages out of which Stage 3 and Stage 4 are Deep sleep i.e brain waves are very slow and highly predictable
- Storing, removing of unnecessary data and strengthening of existing data by connecting different parts of brain takes place here. (Like a cache system in our computers, moving from temporary memory to more permanent memory)
- Occurs more during the first half of sleep
REM Sleep (Dream sleep, Paradoxical sleep)
- Brain waves are fast, unpredictable (which represents as if we are awake, therefore called paradoxical sleep) but our sense organs have no response (i.e the connection between sense organs to brain gets deactivated). In short, during this sleep, we become paralyzed
- Helps in creativity, cognition tasks
- Occurs more during the second half of sleep
- Dreams occur here. Acts like a night time theater where you sit as an audience and the movie played will be “Your life” (though it is NOT JUST REPLAY of your real life incidents)
Debunking common questions/myths
Does sleep really have a purpose?
Yes. In short, this 33% of your life decides the rest 67% in all aspects (physical, mental, emotional, psychological).
Simply speaking, if it does not have a purpose, we might not have evolved it.
Does dreams really have purpose or do they just come?
Obviously they have purpose. In short, dreams nurture our emotions and improves creativity. The famous quote “Time heals all wounds” can be rephrased as “Time that is spent in dreams heals all wounds”.
Why old people can not remember many things?
Neuron connections get weaker → Production of deep NREM sleep reduces → storage efficiency reduces →Cannot remember many things.
But a different perspective is, old people’s brain is very good in “Caching” i.e effective at memory organization. So, before shouting at your granny that they have forgotten, remember that your cache is pretty bad i.e you are storing lots of garbage.
Why teenagers want to stay awake till late night/have trouble going to bed early?
Melatonin (which says when to sleep) levels reduces in teenagers so they have trouble going to bed early.
Why do we love the snooze button?
We all love that “5-minute nap” that we get from hitting the snooze button. Once we wake up, we feel as if we have slept an hour. The reason might be you are already in dream sleep (REM comes more at morning) and dreams run slower (0.5x time maybe). So, you feel you are sleeping for more time.
Why does Jet lag occur?
When you travel from one time zone to another, though the external clock varies, your internal biological clock takes time to get sync with the external one.
Assume A is in New Delhi → Saturday 8 AM and your biological clock is in sync with this
Flight to New York, 24 hr journey →Time in Delhi is Sunday 8 AM and in New York it is Saturday 10 PM (as there is an appx 10 hr delay with New Delhi). And a reverse travel by B
Your biological clock is in sync with New Delhi, so you feel awake (feeling it as 8 AM) though people in New York start sleeping (as it is 10 PM). This is the main source of jet lag and it takes few days for this to disappear. Also, jet lag associated with eastward journey is far worse as the circadian rhythm is slightly longer than 24 hours and traveling east shortens the days while traveling west lengthens them. It means your circadian rhythm needs to do more to catch up.
Is coffee good or bad for sleep?
In short, it depends on individual (because of enzymes), but as a general note not recommended at least 4–6 hr before bedtime. Caffeine has the capability to hold the adenosine for longer time (i.e from our analogy, adds strength to dam to hold water for more time, thus allowing accumulation for longer). But once the caffeine goes out (dams open up), the adenosine floods over causing high lethargy (floods and destruction).
What about alcohol, sleeping pills?
In short, not recommended. They disrupt the natural cycle and has many side-effects (both short and long term). One particular purpose of sleep is to rewire/strengthen connections and intake of these just weakens the connections thus being a “memory eraser”. That is the reason for forgetfulness.
What about smartphones? Is it true that they destroy sleep cycles?
Smartphones emit blue light (whose wavelength is shorter) and our eyes do not filter out blue light. So, as we use blue light emitting devices, our internal clock feels as if it is day (maybe 5 PM) but in real world it might be night (maybe 9 PM). So, our internal clock won’t induce sleep and thus this vicious cycle adds up and destroys sleep cycles.
So, the general advice is to avoid screens atleast one hour before sleep. Another alternative is to use blue light filters (glasses or screens etc;)
Is it good to do exercise before bedtime. What about hot bath or cold bath?
Exercise → Increases body temperature
To get sleep →Body temperature should reduce
So, exercise before bedtime is not recommended. Therefore it is also recommended to do hot bath before sleep because it aids in reducing the body temperature
I do a lot of work thus get less sleep (maybe 4 hr/day) during weekdays. But I sleep more (14hr/day) during weekends thus average remains same. So, am I good?
Unfortunately, sleep is not a bank i.e where you can put some money (i.e sleep less) and collect it later with interest (i.e sleep more). Once you are sleep deprived, you are always sleep deprived no matter what and a continuous sleep deprivation has its own consequences on physical, mental and emotional health.
In fact the late night sleep deprivation and early morning sleep deprivation has different effects as the sleep cycles (REM and NREM) are not distributed uniformly. Late night deprivation effects NREM more and early morning deprivation effects REM more.
What if I avoid sleeping for one full night?
Simply, it will have severe consequences on your upcoming days and if you make it as a habit, it will effect in long run as well. You start forgetting many things, rational thinking reduces, emotionally becomes weak etc;
Night Owl vs Early bird. Which is better?
There is no clear evidence that one is better than the other but the general argument is: Before the advent of technology (i.e lights, smart phones), early humans used to sleep before 10 PM (because they don’t have much to do)
So, the author’s general suggestion is “A sound good night sleep” but it highly varies for every individual.
Is sleeping once a day (long 7–9 hrs i.e Monophasic) or taking short naps (Biphasic) preferred?
Early humans used to sleep in biphasic (a 6–8 hr sleep at night and 1 hr naps in the noon). Due to the busy nature of the modern world, we transformed into monophasic (a long 7–9 hr sleep). Monophasic may not have many disadvantages to health but biphasic has few benefits i.e helps in memory building, gives a break from schedules and rejuvenates for the next tasks.
If you remember, in your school days, you may be allowed to sleep for 30 min to 1 hr after your lunch. Also, you may feel sleepy during your afternoon meetings or classes, but that’s not entirely your fault. Evolution has a role to play. Also, famous people including Edison, Tesla used to do biphasic sleep.
Often, I work on a problem so hard, can’t solve it, go to sleep and cracks it easily after waking up. Does it had to do anything with sleep or is it pure serendipity?
Definitely it is not always pure serendipity. Sleep (especially REM) helps in looking for different parts of brain, fetches various information and tries to make a pattern thus solving your particular problem. In fact the famous quote “Practice makes human perfect” can be rephrased as “Practice with sleep makes human perfect”
How many hours is ideal to sleep?
The author suggests nothing less than 7 hrs based on his research and the recommendation by National Sleep Foundation (NSF)
Many claim that they sleep <6 hr or so and lead a pretty cool life. So, is it really possible? If so, is it advisable?
It is true and possible that one can reduce sleep and still perform great in their daily activities. Many reasons including genetic (DEC2 gene helps reduction in sleep), exercises, proper diet helps to achieve this. But the author does not recommend nothing less than 7 hr of daily sleep because it has adverse effects in later stages of life (which he supports with experimental data).
Nevertheless, it is an individual’s decision to learn his/her body necessities and give enough sleep. In fact “For every rule, there is an exception”
The book has technical aspects explaining lots of experiments but is an easy read and mostly explained in layman terms. This blog tries to touch the tip of the ice-berg and reading the book is highly encouraged to explore more on sleep, dreams and the science behind those along with detailed experiments.
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