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October 2 - October 16, 2022
sleep is infinitely more complex, profoundly more interesting, and strikingly health-relevant.
The first factor is a signal beamed out from your internal twenty-four-hour clock located deep within your brain.
The second factor is a chemical substance that builds up in your brain and creates a “sleep pressure.”
Adenosine
twenty-four-hour rhythm, also known as your circadian rhythm.
The plant didn’t just have a circadian rhythm, it had an “endogenous,” or self-generated, rhythm.
the circadian rhythm—that is, one that is approximately, or around, one day in length, and not precisely one day.
Any signal that the brain uses for the purpose of clock resetting is termed a zeitgeber, from the German “time giver” or “synchronizer.”
The twenty-four-hour biological clock sitting in the middle of your brain is called the suprachiasmatic (pronounced soo-pra-kai-as-MAT-ik) nucleus.
The longer you are awake, the more adenosine will accumulate. Think of adenosine as a chemical barometer that continuously registers the amount of elapsed time since you woke up this morning.
Caffeine works by successfully battling with adenosine for the privilege of latching on to adenosine welcome sites—or receptors—in the brain.
Sleep will not come easily or be smooth throughout the night as your brain continues its battle against the opposing force of caffeine.
When you don’t get enough sleep, one consequence among many is that adenosine concentrations remain too high.
They named these sleep stages based on their defining ocular features: non–rapid eye movement, or NREM, sleep, and rapid eye movement, or REM, sleep.
The steady, slow, synchronous waves that sweep across the brain during deep sleep open up communication possibilities between distant regions of the brain, allowing them to collaboratively send and receive their different repositories of stored experience.
We therefore consider waking brainwave activity as that principally concerned with the reception of the outside sensory world, while the state of deep NREM slow-wave sleep donates a state of inward reflection—one that fosters information transfer and the distillation of memories.
The brain paralyzes the body so the mind can dream safely.
That humans (and all other species) can never “sleep back” that which we have previously lost is one of the most important take-homes of this book,
This humble passerine bird has evolved an extraordinary biological cloak of resilience to total sleep deprivation: one that it deploys only during a time of great survival necessity.
From a prescription written long ago in our ancestral genetic code, the practice of natural biphasic sleep, and a healthy diet, appear to be the keys to a long-sustained life.
There are species that have more total REM time than hominids, but there are none who power up and lavish such vast proportions of REM sleep onto such a complex, richly interconnected brain as we Homo sapiens do.
But in utero, the immature fetus’s brain has yet to construct the REM-sleep muscle-inhibiting system adults have in place.
An infant brain without sleep will be a brain ever underconstructed.
as individuals get older, their brains do not deteriorate uniformly. Instead, some parts of the brain start losing neurons much earlier and far faster than other parts of the brain—a process called atrophy.
Poor memory and poor sleep in old age are therefore not coincidental, but rather significantly interrelated.
Recently, we identified one factor—a sticky, toxic protein that builds up in the brain called beta-amyloid that is a key cause of Alzheimer’s disease: a discovery discussed in the next several chapters.
memorizing someone’s name, a new phone number, or where you parked your car—a region of the brain called the hippocampus helps apprehend these passing experiences and binds their details together.
The memory refreshment was related to lighter, stage 2 NREM sleep, and specifically the short, powerful bursts of electrical activity called sleep spindles,
2 nrem for memory refreshment
the anatomical dialogue established during NREM sleep (using sleep spindles and slow waves) between the hippocampus and cortex is elegantly synergistic.
Like a computer hard drive where some files have become corrupted and inaccessible, sleep offers a recovery service at night.
Success has come in two forms: sleep stimulation, and targeted memory reactivation.
Said another way, forgetting is the price we pay for remembering.
Sleep powerfully, yet very selectively, boosted the retention of those words previously tagged for “remembering,” yet actively avoided the strengthening of those memories tagged for “forgetting.”
The activity circles between the memory storage site (the hippocampus) and those regions that program the decision of intentionality (in the frontal lobe), such as “This is important” or “This is irrelevant.”
It is of little surprise that we see a spike in stage 2 NREM sleep, including sleep spindles, right around the infant’s time of transition from crawling to walking.
We are, as you will see, socially, organizationally, economically, physically, behaviorally, nutritionally, linguistically, cognitively, and emotionally dependent upon sleep.
The second, more common cause is a momentary lapse in concentration, called a microsleep.
Slowness was not the most sensitive signature of sleepiness, entirely missed responses were.
The heady cocktail of sleep loss and alcohol was not additive, but instead multiplicative.
The manifold effect of sleep depravation combined with drinking alcohol
Part of the explanation appears to lie in their genetics, specifically a sub-variant of a gene called BHLHE41.
Individuals who can function normally with only 6hrs of sleep
amygdala—a key hot spot for triggering strong emotions such as anger and rage, and linked to the fight-or-flight response—showed
We discovered that different deep emotional centers in the brain just above and behind the amygdala, called the striatum—associated with impulsivity and reward, and bathed by the chemical dopamine—had become hyperactive in sleep-deprived individuals in response to the rewarding, pleasurable experiences.
There is no major psychiatric condition in which sleep is normal. This is true of depression, anxiety, post-traumatic stress disorder (PTSD), schizophrenia, and bipolar disorder (once known as manic depression).
many of the genes that show abnormalities in psychiatric illnesses are the same genes that help control sleep and our circadian rhythms.
he is what we call “densely amnesic.”
Memento, Ghajini
Even the most elemental units of the learning process—the production of proteins that form the building blocks of memories within these synapses—are stunted by the state of sleep loss.
sleep is not like the bank. You cannot accumulate a debt and hope to pay it off at a later point in time. Sleep for memory consolidation is an all-or-nothing event.
Sleeping all night after learning is crucial to the retention
Chronic sleep deprivation is now recognized as one of the major contributors to the escalation of type 2 diabetes throughout first-world countries.
Leptin signals a sense of feeling full. When circulating levels of leptin are high, your appetite is blunted and you don’t feel like eating. Ghrelin, in contrast, triggers a strong sensation of hunger.
As Van Cauter has elegantly described to me, a sleep-deprived body will cry famine in the midst of plenty.
When you are not getting enough sleep, the body becomes especially stingy about giving up fat. Instead, muscle mass is depleted while fat is retained.
