Matthew Walker is a professor of neuroscience and Psychology at the University of California, Berkely, the Director of its Sleep and Neuroimaging laboratory. He was a former professor of Psychiatry at Harvard University. He has published more than a 100 scientific studies. This book was first published in 2017.
We start with a great quote "Sleep is a non negotiable biological necessity."
I have written a blog post ' A mystery called sleep' recently. Then , you may wonder, why again a blog or a book review on the same subject of sleep. Since, I am fascinated to know that sleep is one of the main pillars to keep our brain sharp at any age and this book intrigued me and gave me deeper insights into the benefits of sleep based purely on scientific facts and laboratory experiments.
Through this blog , I strive to inform the readers about the contemporary deeper knowledge on sleep, its health benefits, ill effects, if not taken seriously.
About the book
The book is divided into 4 parts and 16 chapters. Part 1 covers ' The thing called sleep', Part 2 covers ' Why should you sleep' , Part 3 covers 'How and why we dream' and the 4th part covers 'From sleeping pills to society transformed'
The special feature of this book is that all the information, facts and the statistics provided are based on the results from the studies and experiments conducted at the author's sleep laboratory at the University of California, Berkely and from other reputed sleep laboratories in the USA and other parts of the world.
Before getting into the aspects of sleep, I would like to add some pictures about the brain and its components which are referred frequently in this book.
Fig.1: Three main parts of the brain: Cerebrum, Cerebellum and the brainstem
Fig.2 : The lobes of the Cerebrum
Fig.3 : Limbic System
The thing called sleep :
We know the functions of three basic biological drives in life - to eat, to drink and to reproduce. But the fourth biological drive, sleep, continued to elude science. Through an explosion of discoveries over the past 25 years, it is understood that sleep dispenses of multitude of health benefits for our brain and the body.
There are two factors that determine when you want to sleep and when you want to be awake.
The first factor is the signal (twenty - four - hour circadian rhythm) beamed out from our internal twenty four hour clock, called suprachiasmatic nucleus ( SCN) located in the anterior region of the hypothalamus (Fig.3). Instructed by the SCN, the pineal gland situated at the back of the brain (fig.3), releases a hormone called melatonin, soon after dusk. Melatonin acts like a bullhorn, shouting out a clear message to the brain and the body: 'it is dark', 'it is dark'. At this moment we have been served with a writ of night time, and with it , a biological command for the timing of sleep onset. With dawn as sunlight enters the brain through the eyes, a brake pedal is applied to the pineal gland thereby shutting off the release of melatonin.
The profile of melatonin release ( pg/ml - picogram per milliliter)
The second is the chemical substance called adenosine builds up in our brain and creates a 'sleep pressure'. It will continue to increase in concentration with every waking minute that elapses. When adenosine concentration peak, an irresistible urge for slumber will take hold. It happens to most people after twelve to sixteen hours of being awake.
The two factors that determine the sleep and wakefulness are two different systems, ignorant of each other, though they are not coupled but they are usually aligned.
Two factors regulating the sleep and wakefulness
The urge to be awake
The urge to sleep
Two types of sleep:
The gold - standard scientific verification of sleep requires recording of signals, using electrodes, arising from three different regions namely, brainwave activity, eye movement activity and muscle activity. It was using these collection of measures, the most important discovery of sleep research was made in 1952 at the University of Chicago by Eugene Aserinsky and professor Nathaniel Kleitman
During this research, they observed that there are two phases of slumber (sleep with eye movements and sleep with no eye movements), that would repeat in a somewhat regular pattern through out the night over and over again. They named these sleep stages based on their defining ocular features as non - rapid eye movement (NREM) and rapid eye movement (REM) sleep.
They further demonstrated that REM sleep, in which brain activity was almost identical to that when we are awake, was intimately connected to the experience we call dreaming, and is often described as dream sleep.
NREM sleep is subdivided into four separate stages, named NREM stages1to 4 increasing in their depth. Stages 3 and 4 are the deepest stages of NREM sleep we experience, with increasing difficulty to wake up an individual out of NREM sleep stages 3 and 4 compared to NREM stages1or 2
The sleep cycle between NREM and REM sleep takes approximately 90 minutes. We can observe that the ratio of NREM sleep to REM sleep within each 90 minutes cycle changes dramatically across the night. In cycle1vast majority of the 90 minute cycle is consumed by NREM sleep , whereas Cycle 5, is the REM - rich type of sleep.
The architecture of sleep (hypnogram)
As of now, we do not have scientific consensus as to why our sleep cycles are dramatically asymmetrical in pattern. The key function of NREM sleep is to do the work of weeding out and removing unnecessary neural connections. In contrast, REM sleep plays a role in strengthening these connections. In this way, sleep can elegantly manage and solve our memory storage crisis, with the general excavatory force of NREM sleep dominating early, after which, the etching hands of REM sleep blends, interconnects and add details.
The following are the pattern of brain waves recorded in the University of California, Berkely sleep laboratory. Each line represents 30 seconds of brainwave activity. Details about the methodology of recording the brain waves are explained in the book.
The brain waves of wake and sleep
Deep NREM sleep brain waves are generated in the middle of the frontal lobe (Fig. 2) and sweep across the brain. To identify the site of origin of the NREM sleep brain wave generation, just place your finger between your eyes, just above the bridge of your nose, and slide it up your forehead about two inches. Back in 1950s and 60s, scientists began measuring the NREM brain waves on the assumption that they would get a lazy-looking brainwave activity that must reflect the brain that is idle or dormant at this stage. But, what was received was a stunning act of neural synchrony in which many thousands of brain cells unite and displayed a highly active wave as shown above. At this stage, one would loose the external consciousness since, the thalamus (Fig.3), the sensory gate blocks the transfer of perceptual signals (sound, sight , touch etc.) up to the top of the brain or the cortex. By severing the perceptual ties with the outside world, not only we loose our sense of consciousness, this also allows the cortex to relax into its default mode of functioning.
REM sleep brain activity is an almost a perfect replica of that seen during attentive, alert wakefulness (see fig. above). Hence, REM sleep is called paradoxical sleep : a brain that appears awake, yet a body that is clearly asleep. As is the case when we are awake, the sensory gate of the thalamus once again swings open during the REM sleep. But the nature of the gate is different. It is not the sensations from the outside world that are allowed to journey to the cortex during REM sleep. Rather, signals of emotions, motivations and memories ( present and past) are all played out on the big screens of our visual, auditory, and kinesthetic sensory cortices in the brain. During REM sleep period, muscle tension disappears and we are completely paralyzed and no tone in the voluntary muscles of the body and only involuntary muscles that control our breathing will continue to operate.
When it comes to information processing, the wake state is reception (experiencing and constantly learning the world around you), NREM sleep as reflection (storing and strengthening of those raw ingredients of new facts and skills), and REM sleep as integration (interconnecting these raw ingredients with each other, with all past experiences, building innovative insights and problem solving abilities).
Benefits of NREM and REM sleep:
Major benefits of sleep as found out by the sleep researchers are memory consolidation, motor skill enhancement and creativity.
Numerous functions of the brain are restored by, and depend upon, sleep. Each stage of sleep - light NREM sleep, deep NREM sleep and REM sleep - offer different brain benefits at different times of night.
Of the many benefits conferred by sleep on the brain, that of memory is especially impressive. Sleep has proven as a memory aid: both before learning, to prepare your brain for initially making new memories, and after learning, to cement those memories and prevent forgetting. Through recent researches, sleep scientists can understand 'how' sleep helps to solidify new memories
For fact - based information (text book learning, memorizing names, phone numbers etc.), a region in the brain called hippocampus (fig.3) binds the information together, but, it has a limited storage capacity. During lighter, stage 2 NREM sleep, brain waves kept weaving a path back and forth between the hippocampus and the long time storage site of the cortex thus shifting the fact based information to the cortex. Each night, the long range brain waves of deep sleep will move memory pockets (recent experiences) from a short range storage site, which is fragile, to a more permanent, and thus safer, long term storage location.
Stage 2 NREM sleep, especially the last two hours of an eight hour night of sleep is responsible for the overnight motor - skill enhancement
A final benefit of sleep for memory is arguably the most benefit of all : creativity happens during the dreaming state - REM sleep.
REM Sleep and dreaming:
The brain state called REM sleep and the mental experience that goes along with it (hallucinogenic, motoric, emotional and bizarre), dreaming, are normal biological and psychological process.
The first function of REM sleep involves nursing our emotional and mental health and the second is the problem solving and creativity.
During REM sleep, the prefrontal cortex of the brain (fig.2), the region that manages the rational thought and logical decision making, sending top down instructions to the primitive deep-brain centers, such as those instigating emotions is deactivated. Therefore, REM sleep can be characterized by strong activation in visual, motor, emotional and autobiographical memory regions of the brain.
'Time will heal all wounds' is the age old wisdom/adage. Perhaps, it was not time that heals all wounds, but rather time spent in dream sleep. REM - sleep dreaming takes the painful sting out of difficult, even traumatic, emotional episodes one has experienced during the day, offering emotional resolution, when you awake the next morning due to astonishing change in the chemical cocktail of the brain that takes place during the REM sleep. Concentrations of a key stress related chemical called noradrenaline are completely shut-off within your brain when you are entering the dreaming sleep state. The brain during the REM sleep is reprocessing upsetting memory experiences and themes in the neurochemically calm (low noradrenaline), safe dreaming brain environment. Is the REM sleep, a nocturnal soothing balm that removes the emotional sharp edges of our daily lives?. It seems so, from everything the neurobiology and neurophysiology is telling us.
A second brain advantage gifted by REM sleep is the function of accurately reading expressions and emotions of faces of others. Facial expressions represent one of the most important signals in our environment. They communicate the emotional state and intent of an individual and, if we interpret them correctly, it influence our behavior in return. Our forefathers have said this in a beautiful adage in Tamil ' 'அகத்தின் அழகு முகத்தில் தெரியும்'. There are regions of our brain whose job is to read and decode the value and meaning of emotional signals, especially faces. And it is that very same essential set of brain regions, or network, that REM sleep recalibrates at night.
Aside from being a stoic sentinel that guards your sanity, and emotional well-being, REM sleep and the act of dreaming have another distinct benefit: intelligent information processing that inspires creativity and promotes problem solving. Deep NREM sleep strengthens individual memories, but it is REM sleep that offers the complementary benefit of fusing and blending those elemental ingredients together in abstract and highly novel ways. During the sleep state, our brain will cogitate vast swaths of acquired knowledge and then extract overreaching rules and commonalities. We awake with a revised mind/brain that is capable of divining solutions to previously impenetrable problems.
Ill effects of lack of sleep :
Sleep loss inflicts numerous neurological and psychiatric conditions ( e.g. Alzheimer's disease, anxiety, depression, bi-polar disorder, suicide, stroke, and chronic pain) and physiological disorders and disease (e.g. Cancer, diabetes, heart attacks, infertility, weight gain, obesity, and immune deficiency) - all the ill effects are explained vividly in the book with research data and analyses.
One brain function which buckles under the smallest dose of sleep deprivation is concentration, which playout most obviously and fatally in the form drowsy driving.
Findings from AAA foundation in Washington, DC, 2016
Fantastic Facts :
In 1938, Prof. Nathaniel Kleitman and Bruce Richardson of University of Chicago, stayed in Mammoth Cave in Kentucky, one of the deepest caverns in the planet for 32 days and a sleep research studies on themselves to prove to the world that humans have an internally generated Circadian Rhythm.
Image from Mammoth cave sleep experiment
The emotional regions of the brain, especially the amygdala and the cingulate cortex, a ribbon of tissue sits above the amygdala and lines the inner surface of the brain are up to 30% more active in REM sleep compared to when we are awake.
It is believed that REM sleep dreaming of Dmitri Mendeleev, the Russian chemist of renowned ingenuity led to the invention of Periodic table of elements on 17th February 1869.
Dimitri Mendeleev
As a parting shot, knowing the creative brilliance of dreaming , it is indeed the ingenuine way of our former President, Dr. Abdul Kalam's call to children to " dream, dream, dream", is to unleash their potential of creativity .
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