Multi-Disciplinary Reading – Book Reviews

Why we sleep, Matthew Walker, 2017 – This is pretty much the only book you need to read to understand sleep and such all encompassing books add great value in terms of time spent, especially when the benefits of getting it right are so great.

My notes –

• 2/3rd of adults in developed nations fail to get 8 hrs of sleep

• Insufficient sleep is a key indicator for Alzheimer’s. Less than 6 hours for long time has cancer risk

• Even moderate sleep reductions for a week disrupts blood sugar levels

• The shorter you sleep, the shorter your lifespan

• Every species known to man sleeps – even the ones in harsh environments because the benefits of sleep far outweigh other hazards

• Our bodies have a 24 hour clock that controls the circadian rhythm to be in sync with the day-night cycle. Even plants have their own internal time

• Our internal clocks aren’t perfect and sometimes run for 26 or 28 hours. When exposed to daylight, our body resets these errors (other external cues like exercise, temperature fluctuations, regular social interactions also help reset the clock – that’s why blind people still can regulate their clocks)

• Diurnal species – species active during the day vs noctural ones during the night

• Our circadian rhythms helps drops the body temperature in an almost sinusoidal curve prior to sleep which troughs 2 hours post sleep

• Not everyone’s rhythm is in sync. Morning types are wakeful early in the day at dawn and feel sleep pressure early in the night. They make up 40%. 30% are evening types that sleep late and wake up late and rest lie in-between (Driven mostly by genetics, so night owls can’t be morning types – night owls probably stayed up to protect species)

• Owls suffer the most due to job schedules with higher rates of depression, anxiety, diabetes, cancer, heart attack and stroke

• Melatonin communicates the signal of day vs night through the body. It maintains timing but doesn’t really help in sleep (Levels start rising from early evening and peaks at 4am and drops to lowest at 7am and stays so till 6pm)

• Suprachiasmic nucleus (our clock that maintains the rhythm), can adjust by 1 hour a day when we are in a new timezone

• Frequent timezone shifts destroys learning and short-term memory – based on stydies on airplane cabin crews

• While melatonin doesn’t control sleep, it is adenosine that does. It starts building up in the brain for every waking hour from the morning. When adenosine concentrations peak, we feel sleepy (takes 12-16 hours)

• Caffeine interferes with the way adenosine works by blocking receptors. Caffeine has a half-life of 5-7 hours (time it takes to cut concentration by half). So its not advisable to drink coffee post 4pm

• Most people with insomnia just have a caffeine problem

• When caffeine concentration falls, the adenosine that built up during the time hits suddenly causing a caffeine crash (sudden onset of sleepiness)

• Circadian rhythm and Melatonin decrease signaling end of day and adenosine build up signaling time to sleep don’t work in perfect sync

• 8 hrs of healthy sleep purges the adenosine built up. Inadequate sleep doesn’t purge fully and hence we feel sleepy the next day during mid-day

• Melatonin follows a sinusoidal curve irrespective of whether you had sleep or not but adenosine can continue climbing when not had addequate sleep. We feel most sleepy when the diff between melatonin and adenosine is very high. So when we skip sleep for one night, when melatonin peaks next day, we may actually be able to overcome sleep or feel less sleepy than we would have felt earlier in the day when melatonin levels were low (Fascinating stuff that looks easy to understand from chart)

• Are you getting enough sleep? If you are feeling sleepy by 11am, then NO (Not enough adenosine purged). If you need caffeine before noon to function normally, definitely NO (Blocking adenosine with caffeine).

• Sleep obligations that aren’t paid off are carried over to the next day and the next and so on, eventually leading to chronic fatigue leading to mental and physical ailment, mostly in industrialized nations

• Common sleep disorders – insomnia and sleep apnea (snoring and disordered breathing)

• When we sleep, thalamus in the brain blocks the sensory gates.

• We lose track of time consciously when we sleep but our body still maintains time precisely (hence we wake up at 5:58am for an alarm we set at 6am)

• Time isn’t time within dreams as we experience time dilation

• When we sleep, our brain replays the patterns we learnt during the day. This is how we actually learn – by getting adequate sleep

• We have two distinct sleep cycles when we sleep. One called REM and another NREM (non-REM). REM = Rapid Eye Movement

• REM and NREM alternate through-out the night in 90 min cycles. Early in the night we spent more time in NREM than REM but later in the morning, we spend more time in REM per 90 min cycle (hypnogram chart in book shows this nicely)

• NREM sleep weeds out unnecessary neural connections while REM sleep strengthens them. By alternating, we manage the finite space in our brain.

• When we wake ourselves up early after sleeping late, even if we lose 2 hours or 25% of sleep time, we lose bulk of the REM sleep in the last cycle (severely affect our ability to learn)

• During NREM sleep, brain activity is synchronous, like the neurons are all singing together. This is where distillation of memories happens. Distant parts of the brain communicate and new insights may emerge.

• In REM sleep, the brain completely paralyses the body (atonia), opens the sensory gate of the thalamus but instead of outside sensations, its our memories that get played back. If NREM state is “reflection”, REM sleep is “integration” – building an accurate model of how the world works. The brain paralyses the body so we can dream safely. It fuels creativity and we tend to wake up with solutions to intractable problems

• Every species sleeps and has done so since at least 500 million years ago from the Cambrian explosion. Even unicellular organisms that last beyond 24 hrs have a active/passive phase based on light/dark cycle of the planet

• Sleep was the first state of life on the planet. It was from sleep that wakefulness emerged

• Although all animals sleep, their REM/NREM composition is different. REM sleep is present only in birds and mammals. So its newer in the evolution chain

• In unfamiliar environments like a new hotel room, one half of the brain sleeps little less than the other to stay vigilant

• Individuals who are deliberately fasting will sleep less as the brain is tricked into thinking food is scarce

• Monophasic vs Biphasic sleep – one block of time vs two blocks. Most cultures sleep in the noon post meal (Greeks and mediterraneans with their siesta). Abandoning siestas increase risk from heart disease in these societies

• Fire helped us sleep on the ground safely. This also perhaps led to REM sleep and consequently, our domination

• REM sleep is like the high-speed ISP that connects different neighborhoods (synaptogenesis). Babies spend most of their sleep in REM state

• Excess amounts of connectivity in some parts and deficiency in others occurs during early development in people with Autism. Autistic children also have weak melatonin cycles

• Alcohol is one of the most powerful suppressors of REM sleep

• REM/NREM composition varies through childhood. First year its mostly REM, then mid to late childhood is mostly NREM and reduces post puberty. Rationality is one of the last things to fluorish in teenagers until this pruning happens

• REM sleep largely remains stable through adult life but NREM sleep reduces (poor memory in older age)

• Hippocampus stores memories temporarily. When we sleep, it gets into the cortex for long-term storage

• Sleep helps to forget what we need to forget. It also helps to reinforce skills without further practice. (People who play instruments will vouch for this)

• You do not know how sleep-deprived you are when you are sleep-deprived

• Emotional irrationality is a key problem without sleep as the amygdala’s emotional gas pedal isn’t countered by the pre-frontal cortex’s brake

• Depression is not presence of excessive negative feelings. It is the inability to experience positive emotions (anhedonia) in food, socializing or sex

• The best bridge between despair and hope is a good night’s sleep (Cossman)

• Heart disease, obsesity, dementia, diabetes, cancer all have causal links with lack of sleep

• Those sleeping 6 hours or less were 400-500% more likely to suffer one or more cardiac arrests than the one that sleep in excess

• The less you sleep, the more you are likely to eat high-cal foods and develop type-2 diabetes. Also body depletes muscle instead of fat when you don’t get enough sleep

• Leptin and Ghrelin regulate our appetite. More letin = blunted appetite. More ghrelin = strong hunger

• Lack of sleep depresses immunity to the tune of increasing infection rate to 50% vs 18% in non-sleep deprived individuals for the same virus

• Chronic inflammation causes a lot of health problems, including cancer

• Its not time that heals wounds. Its time spent in dream sleep (Sedatives and alcohol may help us sleep but not heal as they interfere with REM sleep. Also sedation is not sleep)

• What most people think as Insomnia isn’t inability to sleep – it is mostly people not giving themselves the opportunity to sleep. Clinical insomnia is inability to “generate” sleep

• Constant LED light from screens (esp blue light suppresses melatonin, making you think its still day), regularized temperature, caffiene, alcohol and alarm clocks cause sleep troubles. One must get to bed only when sleepy and avoid spending non-sleep time in bed

• Bath prior to sleep helps bring blood to the surface. Exposed hands, feet and face help radiating heat outwards reducing body temp and helps sleep

• REM sleep is what stands between rationality and insanity

• 50% of children with ADHD diagnosis actually have sleep disorders

• Tips for good sleep – 1. stick to sleep schedule 2. exercise but not too late in the day 3.avoid caffeine and nicotine 4. no alcohol before bed 5. avoid large meals late at night 6. avoid medicines that disrupt sleep 7. no naps after 3 pm 8. relax before bed with a book or music 9. hot bath before bed 10. dark, cool, gadget-free bedroom without clocks 11. right sunlight exposure 12. avoid bed when not sleeping

Sleep is the easiest way to improve quality of life, reduce disease, be mentally agile, creative and yet its the one most of us focus the least on. Matthew Walker covers everything around sleep in great depth and the message is clear – get your 8 hours of sleep per day without fail no matter what. You won’t regret the time spent and if the book makes you sleepy, well it has achieved what it set out to do. 9/10