1/3 of adults don’t get enough. A lot of bad things happen from not getting the right amount. We are only species to restrict sleep without gain. If sleep does not provide a vital purpose, then it’s the biggest evolutionary mistake in the history of nature (we are vulnerable when sleeping). There is no process in brain or major organ that isn’t helped by sleep. Most effective thing we can do to restore our body and brain health each day.
Circadian rhythm is the sleep drive at night and waking cycle in the day. Living organisms keep their own time, not entirely based on daylight, and it’s not exactly 24 hours, but very close. Suprachiasmatic nucleus controls when we want to be asleep or awake. Body coordinates a drop in temperature as bedtime comes, and body temp rises to wake us up again. About 40% of people are “morning people” and it’s a real thing. Strong genetic involvement. Modern work schedules favor morning people.
Melatonin is naturally released at night. Released by pineal gland when it gets dark. Over the counter melatonin has terrible quality control.
People that deal with a lot of jet lag for work have very bad health outcomes (diabetes, cancer etc).
Adenosine builds up all day and causes sleep pressure, a desire to sleep. Adenosine will be blocked temporarily by caffeine by binding to the same set of receptors, but according to the half-life of caffeine, when it wears off you’ll be hit harder by an adenosine rush. Some peoples’ liver clears caffeine faster than others, but it’s about 7 hour half-life. Ie: 50% cleared after 7 hours.
Caffeine is a stimulant. Adenosine and circadian rhythm are independent systems. Adenosine is removed as we sleep, but circadian rhythm doesn’t care whether we sleep or not. Getting enough sleep? Two q’s, could you fall back asleep at 10 or 11am? Can you function optimally without caffeine before noon? Would you sleep past your alarm clock?
Time dilation, time in dreams can feel elongated. The brain keeps track of time while we sleep. NREM vs. REM sleep. REM is dream-sleep.
90 minute cycles, mostly NREM in first half of night. Analogy of sleep as two roles of a sculptor. Take away chunks and then refine. We lose disproportionately more REM sleep if we don't sleep for a full 8 hours.
We get totally paralyzed as we enter REM cycle sleep so muscle tone goes to zero. We don't want to allow the body to act out its dreams, so it's paralyzed during REM.
Total amount of time sleeping varies greatly across animals. No obvious reasons for the difference across many vectors. Composition of NREM and REM is different across species. REM sleep probably emerged twice, in birds and mammals independently.
After sleep deprivation, we try to make up the NREM early on, and REM is overrepresented later in recovering. We can’t fully recover from lost sleep, it’s just gone. Manner of sleep is also different. Some sleep with half a brain like aquatic. Proof that sleep is non-negotiable.
Also different in sleep patterns. Monophasic, once a day. Everybody wants a nap in mid-afternoon. Body wants to be biphasic and have a nap. Greece / Mexico did this still, much later than other countries. We get much more REM than our common evolutionary ancestors. Maybe because we sleep on the ground with fire. Improved emotional IQ and creativity as a result.
Brain is over-populated with neurons at the early stages after birth. Heavy REM dominance at this stage, and disturbing this process is very detrimental. Kids with autism don’t have normal sleep patterns. Melatonin effect is weaker, 30-50% less REM sleep. Causality direction isn’t clear. Alcohol strongly supresses REM sleep. Alcohol concentration in blood and breast milk are similar if drinking. Every hour of REM sleep counts for infants.
Polyphasic sleep profile for infants and children, lots of short cycles with waking between. It takes time for for suprachiasmatic nucleus and circadian rhythm to develop. Five-year olds sleep longer and half more NREM than REM. Analogy of an ISP using a first pass to lay down a rough network that's overzealous and then using usage statistics to determine which households are using the most bandwidth. To save on costs we slowly chip away at the unused infrastructure, as with the brain. Lots of pruning in adolescence. They have a less rational and more risk-tolerant version of an adult brain.
Circadian rhythms run earlier for younger kids. Adolescent teenagers have the opposite, so they actually are inclined to stay up later. No children need caffeine. Instead of seeing sleep as lazy for young adults, important to know how much it's adding.
Most seniors don't realize how much, as their sleep degrades, so does their health. Weakened bladder means more waking and fragmentation with age. Low sleep efficiency (sleep to time in bed ratio), the worse our outcomes.
People with worse deep sleep also have the most likelihood of forgetting things. Lack of memory consolidation occuring. It is a myth that older people need less sleep, they just have a harder time getting good sleep quality and quantity.
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