Author: Dr. Matthew Walker
Date Read: April 2019
Rating: 4/5
2) Caffeine, Jet Lag, and Melatonin
There are two main factors that influence your desire to sleep and wake. The first is a signal beamed out from your internal twenty-four hour clock located deep within your brain. The second is a chemical substance that builds in the brain and creates a ‘sleep pressure’.
circadian rhythm - circa meaning “around”, and dian, a derivative of diam meaning “day”.
The twenty-four hour biological clock sitting in the middle of your brain is call the suprachiasmatic nucleus. It sits just above the the crossing point of the optic nerves stemming from your eyeballs. This time keeping machinery samples the light being sent from each eye as it travels along the optic nerves toward the back of the brain for visual processing. It uses this light to account for any inaccuracies in keeping time and maintain a tight twenty-four hour clock.
Early birds account for roughly 40% of the population, preferring to wake up at or around dawn. Night owla compose about 30% of the population, preferring to go to bed late and wake up in the later morning or even afternoon. The final 30% are somewhere in between, with a slight disposition for the latter.
The prefrontal cortex is the head office of the brain which controls high-level thought, logical reasoning, and emotional stability. This region of the brain can remain in an ‘off-line’ state and can contribute to the sleepiness felt by morning people and night owls alike when first waking up in the morning.
Melatonin is a chemical regulated by the suprachiasmatic nucleus. It is released at night and serves as a signal to the body to sleep.
Sleep pressure is dictated by the chemical adenosine. It accumulates throughout the day as we are awake, peaking around 12-16 hours of being awake.
3) Defining & Generating Sleep
REM - a stage of sleep characterized by rapid eye movement in which humans principally dream.
The gold standard to verify sleep requires the recording of signals, using electrodes, arising from three different regions: (1) brainwave activity, (2) eye movement activity, (3) muscle activity. These signals are collectively grouped together under the blanket term polysomnography meaning a readout of sleep that is made up of multiple signals.
The two stages of sleep, NREM and REM cycle every 90 minutes with varying proportions of each that favors NREM sleep earlier in the night and REM during the later portion of the night.
Author Matthew Walker theorizes that the tug-of-war between NREM and REM sleep is necessary to remodel and update the neural circuits in order to manage the finite storage capacity within our brain. Our brains must find the sweet spot between retention of old information and leaving sufficient room for the new.
How Your Brain Generates Sleep
REM sleep brainwave activity is as frenetic and asynchronous as wehn you are awake. NREM on the other hand, is rhythmic and reliable.
Sleep spindles occur during various stages of NREM sleep, generally on the ‘downbeat’ of a NREM sleep wave cycle and operate as soliders protecting the sleeper from external noises.
REM sleep has also been called paradoxical sleep since our brainwave activity reflects that of being awake yet we are sound asleep.
Information Processing: wake state : reception; NREM : reflection; REM : integration
4) Ape Beds, Dinosaurs, and Napping with Half a Brain
Who Sleeps
“Nothing in biology makes sense except in light of evolution.” - Theodosius Dobzhansky
Considering how biologically damaging the state of wakefulness can be, Walker theorizes that that sleep was the first state of life on this planet, and it was from sleep that wakefulness emerged. So then the question is, Why did life ever bother to wake up?
One of these things is not like the other
The difference in sleep time between different organisms may be linked to the relationship between the size of the nervous system, its complexity, and total body mass, With greater sleep amounts needed by those organisms with greater brain complexity relative to body size.