The second half of Why We Sleep starts like this “Amazing breakthrough! Scientists have discovered a revolutionary new treatment that makes you live longer. It enhances your memory and makes you more creative. It makes you look more attractive. It keeps you slim and lowers food cravings. It protects you from cancer and dementia. It wards off colds and the flu. It lowers your risk of heart attacks and stroke, not to mention diabetes. You’ll even feel happier, less depressed and less anxious. Are you interested?”
Hyperbolic as this may seem, nothing about this fictitious advertisement is inaccurate when it comes to sleep.
All the notes I highlight on sleep below are related to scientific studies performed by Matthew Walker and his team, or others in the scientific community. For ease of writing and reading flow, I won’t note the sources here but I’ll give you the page in the book which elaborates in each case and the book index contains all of the sources.
SLEEP AND LEARNING
- Which sleep confers the greater memory savings benefit? (deep NREM or REM)? An early night, right in deep NREM. (p113)
- Experimental results of Jenkin and Dallenbach have now been replicated time and time again with a memory retention benefit of between 20 and 40 percent being offered by sleep, compared to the same amount of time awake. (p113)
- The more sleep spindles an individual obtains during a nap, the greater the restoration of their learning when they wake up (p110)
- In 2006 a team in Germany ran a study to insert small amounts of electrical voltage during deep sleep. When done pulsing in rhythmic time with the brain’s own waves, both the size of the brain waves and the number of sleep spindles were increased by the stimulation and provided a memory enhancement of 40% over the control group. (don’t try this at home!) (p117)
- A swiss team suspended a bed frame on ropes and rocked the bed from side to side at controlled speeds. Slow rocking increased the depth of deep sleep and boosted the quality of slow brain waves and more than doubled the number of sleep spindles. (p118)
- Using MRI scans, scientists have since looked deep into the brains of participants to see where those memories are being retrieved from before sleep relative to after sleep. Information packets are recalled from completely different locations. Before sleep, participants fetch newly learned information from the hippocampus. After sleep, from the neocortex. (p114)
- Sleep stimulation efforts to date are indiscriminate – that is, you can’t really choose what to remember or what to forget. Science now has a new method called “targeted memory re-activation”. Before going to sleep in this test, participants were shown not just images at different locations and this would be accompanied with a sound (e.g. a meow for an image of a cat). When asleep, participants were played back the sounds on low volume with speakers at either side of their bed. The memories recalled the next day were biased significantly toward those reactivated during sleep using the sound cues. This is the type of thing you could use for some SERIOUS brainwashing. (p119).
- In another experiment, when participants were given words to remember as well as an indicator as to whether to remember or forget the word, after sleep (vs the non sleep group), memory was selectively boosted for those that had been tagged to be remembered.
- Which stage of sleep determines what memories should be priorities vs removed? NREM sleep – and the very quickest of sleep spindles. Eternal Sunshine Of the Spotless Mind here we come! (p122)
SLEEP IMPACT ON OTHER TYPES OF MEMORY
- The term “muscle memory” is a misnomer. Muscles themselves have no suc memory: a muscle that is not connected to a brain cannot perform any skilled actions, now does a muscle store skilled routines. Muscle memory is, in fact, brain memory. Training and strengthening muscle can help you better execute a skilled memory routine, but the memory routine, the memory program – resides exclusively in the brain. (p123)
- In an experiment teaching right handed people to type a number sequence with their left hand, those who slept showed a 20% jump in performance speed and a 35% improvement in accuracy vs those who were tested before bed. Those then tested before bed were re-tested in the morning and got the same bump in performance. So the brain keeps improving skill memories without practice. (p125)
- When the brain transfers skill memories, its not look fact / info based memory, the motor memories are shifted to brain circuits that operate below the level of consciousness. (p127)
- The type of sleep responsible for overnight motor skills enhancement is directly related to the amount of stage 2 NREM, especially in the last two hours of an eight hour night of sleep. (p127)
SLEEP IMPACT ON SPORTS
- The less sleep an athlete has, the higher the the likelihood of injury. At 6 hours average, the change of injury is 72%. What!! Compared to just 18% at 9 hours average sleep or 35% at 8 hours average sleep. (p129)
- One example of this is the difference in an NBA player’s stats when measuring performance on games played on nights after 8 hours or more vs those with less than 8 hours (p130):
- 8 hours or more:
- +12% increase in minutes played
- +29% increase in points/minute
- +2% increase in three-point percentages
- +9% increase i free-throw percentage
- Less than 8 hours:
- +37% increase in turnovrs
- +45% increase in fouls committed
- 8 hours or more:
- At the most dramatic time of motor learning in any human’s life (when we learn to stand and walk as an infant), there is a consistent spike in stage 2 NREM sleep, incring sleep spindles, right around the time of transition from crawling to walking. (p131)
I’m splitting these posts into more parts so you can read it sooner – as at my current rate it might take me a couple of weeks to get through all the notes. The next post will be on the impacts of sleep deprivation and health outcomes and then we’ll move on to the awesome world of dreams!