Ben C. Davis

Chapter 1

• sleep has multiple benefits, it’s complex. There’s no single reason
• It seems to have many regenerative health benefits
• Dreams provide benefits: consoles bad menoeries
• Helps the immune system
• Regulates insulin
• Sleep helps maintain good gut dome
• Sleep massively helps physical activity

Chapter 2

• 2 things influence when we sleep:
  • Circadian rhythm
  • Chemical build up - sleep pressure
• Circadian rhythm is not bad on day and night, although it’s roughly aligned with 24 hours. In humans it runs a little fast.
• It’s an internal clock - it’s not based on anything external.
• But it can be recalibrated by an external influence, notably the daylight cycle. But there can be other influences: activity, eating, even social activity. These influences are more prevalent when daylight is inaccessible, typically blind people.
• Night owls and morning larks: genetically determined to mirror your family in order to increase survival rates
• Melatonin: chemical released by the suprachiasmatic nucleus to control the circadian rhythm. It is released at dusk and continually builds. It doesn’t induce sleep, but it does trigger the rest of the brain and body to go to sleep.
• Sleep pressure - beginning at the beginning of the day, Adenosine is released and builds up on Adenosine receptors. This pushes the body to sleep. Once it builds up beyond a certain threshold it’s hard to hold back from the desire to sleep.
• Caffeine blocks the receptors leading to a relief from drowsiness. Once the coffee has been fully broken down by an enzyme in the liver, the built up adenosine rushes back to the receptors and causes you to crash.
• Adenosine and the circadian rhythm operate independently. It’s why an after an all nighter, the best morning you can get a second window. Adenosine counties to build up but the circadian rhythm carries on unaware.
• Getting enough sleep can be determined by answering two questions: could I fall back asleep by 10/11 am? Do I need caffeine to have any productive time before midday.

Chapter 3

• when you’re asleep you lose perception of the outside world. Your senses are still working, but the thalamus blocks the signals from the reaching the cortex so we don’t perceive them. This is essentially what sleep is.
• The other part of being asleep is time dilation: the sense that the time you’ve been asleep is undetectable.
• 3 types of measures for sleep:
  • Eyebmovement
  • Brain waves
  • Muscles
• Nrem - deep wave sleep, transitioning short term memory to long term memory
  • Slower brain wave activity
  • 4 stages, 3/4 are the deepest stages where it’s the hardest to wake someone
• Rem - replaying memories to form new connections - thalamus lets in senses from memories and emotions
  • Rem - lots of brain wave activity - indistinguishable from being awake
• Sleep cycles
  • Sleep in stages of around 90 minutes, with each stage made up of some nrem and some rem. The first half of the night, deep nrem dominated. The latter half, rem sleep dominates
  • One theory for this is to do with memory storage. We have a finite amount of neurons available for storage. Nrem weeds out the less relevant connections and helps push the most important connections into long terms storage. Rem sleep deepens those connections, strengthens them.
• Electrical patterns for each stage of sleep
  • When awake, electrical signals from the brain are chaotic - many different areas of the brain working independently cause an overall chaotic output
  • During nrem and especially stages 3 & 4, the chaos subsides and instead we see slow deep waves emitted from the neocortex. These waves travel in a single direction towards the back of the brain - it’s understood that these waves are key to memory consolidation. To create these distinct slow waves, 1000s of brain cells have to work in synchrony.
• Rem brain waves
  • Thalamus replays memories emotions and motivations out to the various receptors in the brain - ocular, etc
  • Wake state = reception
  • Nrem = cleansing and deepening connections
  • Rem = integration - building ever more accurate model of how the world work
  • During rem: muscle tension completely relaxed and you’re entirely paralysed

Chapter 4

• sleep is common on almost all creatures
• Even single cell organisms have passive and active cycles that correspond to the daylight cycle
• Total amount of sleep across species is very different and we don’t know why
• Rem doesn’t seem to exist in marine animals, we haven’t detected it
• Some marine animals like dolphins and sole birds use split brain sleep, where different. Parts of their brain will sleep while the other remains vigilant. This is only for nrem. Rem required all sides of the brain. This is for all animals.
• Some migratory birds can sleep for seconds at a time
• Humans are genetically supposed to sleep in 2 separate phases: bi-phasic. This requires an afternoon nap. That’s why we have a drowsy dip in mid afternoon. Yeah hate the second phase
• Western European’s before the modern era would have a couple hours during the middle of the night. This isn’t biological. It’s cultural.
• A mid afternoon nap is the biological second igase
• Rem sleep is 20% of total human sleep, much higher than other animals. This happened because we left the trees and there was evolutionary pressure to sleep for a shorter period of time. This probably led to significant developments in human history: ability to deal wi h complex emotions.
• Rem deepens connections created during nrem. This allows rem to encourage acreativity

Chapter 5

• during pregnancy babies are mostly asleep most of which resembles rem sleep
• This happens because the motor inhibiting system hasn’t developed
• Fetas only awake 2 to 3 hours a day
• Towards the end of pregnancy they get more and more rem. At the peak, 12 hours.
• Rem sleep is used to stimulate growth of the brain. It’s during a period called synapto genesis. There’s a lot of redundancy. Essentially the brain is laying down I sculpted bandwidth to all regions of the brain, later made efficient after usage has determine what’a important.
• Depriving infants of rem sleep seems to significantly damage the development of the brain.
• There are some links of lack of sleep and importantly rem sleep in the development of autism.
• Alcohol effects the sleep of babies in the womb. A study of alcoholic women showed the new borns had less rem sleep. It also showed less quality rem sleep - 200% reduction of brain waves during rem. it’s shown that heavy drinking are connected with psychiatric disorders.
• Even minor amounts of alcohol effect the baby. The same problem effects breast milk. Within the womb: lower heart rate and upset rem sleep.
• Every hour of rem sleep seems to be important.
• Babies are polyphasic. Longer periods as the baby grows.
• When born, the sleep system is built. But the circadian rhythm is not. It’s a pattern matching system that has no inputs yet. So encouraging the correct associations in babies is very important.
• During early childhood, rem sleep decreases and nrem increases, even as total sleep decreases. Infants also become biphasic then monophasic. Finally stabilises 80% nrem, 20% rem.