Author: Matthew Walker
notes
caffeine, jet lag, and melatonin
Summary
The sleep-wake cycle is influenced by the circadian rhythm and sleep pressure.
- Circadian rhythm
- Around 24 hours
- Works on its own without external cues but resets with daylight
- Zeitgeber: any signal the brain uses for clock resetting
- Influences
- Eating and drinking
- Moods
- Urination
- Core body temperature
- Metabolic rate
- Hormones
- Controlled by suprachiasmatic nucleus
- Above optic nerves
- Controls sleep
- Will keep going regardless of whether you have slept or not
- Can only adjust by one hour each day when jetlagged
- Circadian rhythms differ across individuals (Process-C: wake drive)
- Genetic, not by choice
- Impacts performance due to prefrontal cortex activity and bodily functions tied to circadian rhythm
- Distribution
- 40% morning types — morning larks
- 30% evening types — night owls
- 30% in between
- Why?
- Humans co-slept as tribes
- Staggering wake times → collective vulnerability for only 4 hours instead of 8
- Melatonin
- Hormone that signals to body that it’s dark
- Regulates sleep timing, not generation
- Over-the-counter
- Not regulated by FDA
- Ranges from -83% to +478% advertised amount
- Adenosine
- Accumulates while you’re awake (Process-S: sleep drive)
- Causes sleep pressure in high concentrations
- Turns down wake-promoting regions
- Dials up sleep-inducing regions
- Caffeine blocks receptors
- Causes crash after drug clears out
- Sleep debt: lack of adequate sleep means concentrations remain high
- Leads to chronic fatigue
- Signs of sleep deprivation
- You could fall back asleep at 10 or 11am after waking up in the morning
- You cannot function optimally without caffeine before noon
- You would sleep past your intended wake up time if you did not set an alarm
- You need to reread the same sentence over and over
- You forget what color the last few traffic lights were while driving
defining and generating sleep
Summary
Sleep is necessary for processing and integrating new memories. We experience life in the wake state, reflect and organize in NREM sleep, and integrate experiences with past knowledge in REM sleep. We have more NREM sleep early in the night as the brain prunes our neural connections, then more REM sleep later as we strengthen neural connections.
- Thalamus: sensory gate
… sleep may elegantly manage and solve our memory storage crisis, with the general excavatory force of NREM sleep dominating early, after which the etching hand of REM sleep blends, interconnects, and adds details.
- Sleep cycle
- 90 minutes
- Sculpts our memories
- Types of sleep
- NREM: non-rapid eye movement
- Four stages from light to deep
- More in early night
- Weeds out unnecessary neural connections
- Slow-wave sleep: stages 3 & 4
- More synchronous than waking brain activity
- Generated in between frontal lobes
- Travel from front to back of brain
- Neurons fire in time, like a well-coordinated symphony
- Waves transfer memory packets from short-term to long-term storage
- Sleep spindle: burst of brainwave activity at the tail end of individual slow wave
- Shield brain from external noise
- REM: rapid eye movement
- More near the morning
- Strengthens neural connections
- Fast frequency brain activity
- Chaotic
- Response to external stimuli
- NREM: non-rapid eye movement
- Since stages not evenly distributed, sleeping inconsistently can be bad for our health
- Information processing in sleep
- Reception: wake state, experiencing and learning
- Reflection: NREM sleep, storing and strengthening
- Integration: REM sleep, interconnecting experiences with past experiences, building model of world, insights, problem-solving
who sleeps, how do we sleep, and how much?
- Who sleeps?
- All animal species
- Theory: sleep is the default state of life, from which wakefulness emerged