Key takeaway:
All stages of sleep in the correct length are critical for learning, memory, physical repair, and emotional resilience.
Hey, everyone. Coach Mark, here.
This lesson will pop the hood on our sleep patterns and help you have a better understanding of how not all sleep is created equal and how to maximize that precious time we spend in bed.
We are not just immobile bodies at rest while we sleep. Instead, sleep contains thousands of physiological, mental, and emotional processes that are equal to, or even exceed, similar processes during waking hours — each one critical for healthy living, learning, recovery, and aging.
There are two main phases of sleep: REM and non-REM sleep. REM is usually being associated with dreaming. Ideally, the brain and body go through each stage every 90 minutes, four to six times a night.
Let’s dig in a little deeper.
Non-REM sleep occurs in three progressively deeper levels:
N1 – This is the phase where we transition from being awake to falling asleep. It’s that moment in high school when we dozed off in math class and our head dropped from the hand holding it up. It’s also the stage when we sometimes jerk ourselves back awake from those strange whole-body muscle spasms.
We’ll only repeat this phase if we wake up in the middle of the night. It’s this “no man’s land” between being aware that we’re awake and falling into the next stage of sleep.
N2 – Also known as light sleep. This phase is when our body temperature drops and our heart rate begins to slow.
Throughout the following sleep cycles, wavelengths of brain activity, called “sleep spindles,” are believed to be related to refreshment, memory, and our ability to learn. The brain regions involved the most are the hippocampus (the learning and memory structures of the brain. Recall the last module’s look into these structures’ function in recovering from moral injury) and the prefrontal cortex (associated with planning, self-control, decision-making, and complex cognitive behavior). This is why getting too little total sleep makes it difficult to learn and why napping can improve focus and cognitive performance.
N3 – This is also known as deep sleep. Our muscles relax and blood pressure and breathing rate drop. Deep sleep has been shown to be crucial in a number of areas regarding memory and brain health.
It’s during this deep sleep phase, in a process called “memory consolidation,” that the “save” button is pressed on fresh memories from the previous day. The brain also takes this time to integrate complex motor skills, making this stage not just crucial for learning facts and cognitive skills, but also for learning sports, dancing, and playing musical instruments. Deep sleep is also when adaptive hormones flow at their peak, repairing and replenishing muscles, tissues, organs, and bones, as well as restoring physical energy.
A more recent discovery, called the glymphatic system, also kicks in during deep sleep. At this stage, some brain cells are allowed to shrink and the brain is flooded in cerebrospinal fluid, effectively washing away metabolic wastes accumulated during the day. It’s believed that disruptions in this process are associated with Alzheimer’s disease and dementia.
REM sleep:
REM (rapid eye movement) sleep is most often associated with dreaming. Although dreaming can occur in other stages of sleep, it’s during REM sleep that the majority of dreaming takes place and we have our most memorable and vivid dreams, especially those we remember when waking up in the morning.
REM sleep has been extensively studied and has been associated with a number of important cognitive and behavioral processes.
During this phase, our brain becomes more active while our body becomes relaxed and completely immobilized. Under normal conditions, a person does not act out his or her dreams (more information about this in an upcoming lesson).
REM sleep assists problem solving and creativity. That’s why it’s better to “sleep on it” when we have a difficult problem to solve rather than staying up all night spiraling. While dreaming, our brain makes memories collide and interconnect, allowing our subconscious to make new connections and associations that didn’t exist before. It also strengthens these connections and memories, and replenishes cognitive ability.
You know that feeling when an idea or solution suddenly comes to you when you’re daydreaming? Consider REM sleep that same process, but on steroids. It’s absolutely critical for being able to come up with solutions and for creative problem-solving.
On another level, REM sleep acts as an “emotional convalescence” — a time for emotional first aid. Under normal conditions, dreaming is not a simple rewinding and replaying of our waking experiences but rather a play on our emotional themes and concerns.
While dreaming, it’s the only time in our body’s 24-hour cycle when the brain shuts off the stress-related chemical noradrenaline as we mentioned in the previous lesson (adrenaline is a stress hormone in the body, noradrenaline is the brain’s equivalent).
With noradrenaline shut off, along with the reasoning and logical control centers in our prefrontal cortex also turned off, our mind is free to experience anything and everything without us stopping mid-dream to wonder how strange it is that my dog just turned into my grandmother and wants me to feed her kibble. Instead, our brain has now created a safe space for it to take difficult, painful, or even traumatic experiences and replay the emotions and feelings without our reasoning abilities and stress responses. It helps separate the emotions from the waking memory in a soothing neurochemical bath, taking the sharp edges off recent experiences.
This emotional first aid is so crucial that our brain will start to steal it from our waking hours if we’re sleep deprived or have abused alcohol long enough to sufficiently reduce our REM sleep. Stay awake long enough and we will begin to hallucinate. Drink enough alcohol and go for long periods without dream sleep and our brain will develop a build-up and backlog of REM pressure. This pressure will force its way into our waking consciousness in a terrifying way, causing hallucinations and delusions. Alcoholics or those recovering from alcohol abuse will know this as the “delirium tremens.”
Even moderate amounts of alcohol, just a few drinks, can curtail the memory and creativity functions described earlier. A study demonstrated that alcohol consumption reduced the amount learned in memory tasks by 50% if the participants had three drinks the night of the learning and then slept naturally for a couple of nights thereafter. Memory was still reduced by 40% if the participants slept normally for two nights and had the drinks on the third night!
The control group that had no drinks remembered everything they had learned and even demonstrated enhanced abstractions and connections after a few nights of uninterrupted sleep. Think about all the learning we do during the week only to wipe most of it away in the bar on Friday night!
A final note on REM sleep: PTS causes the stress hormones adrenaline and noradrenaline to increase and remain elevated during the day and night, making dreaming less effective. This results in the brain trying to repeat the process over and over, causing repetitive nightmares. (This will be the subject of an upcoming lesson.) The blood pressure medicine Prazosin reduces noradrenaline in the brain and is sometimes prescribed to treat repetitive nightmares.
Sleep cycles:
As mentioned above, a normal night’s sleep will consist of four to six cycles as shown here.
Notice how most of the deep sleep happens earlier in the night, and it gives room for more REM sleep later in the evening and into the morning. In fact, even if we go to bed late, say 2 a.m., and even sleep in, we will still likely suffer from reduced deep sleep and its benefit of peak hormonal cascades.
For example, the release of human growth hormone peaks during deep sleep between 10 p.m. and midnight. Consistently missing deep sleep during these hours can potentially rob us of the adaptation, growth, and repair that our body needs. This will leave us tired and unrecovered from the previous day. Some people even go so far as to claim that every hour of sleep before midnight is worth two hours compared to sleep after midnight. Although not technically true, we still need to get to sleep early enough for our circadian rhythm to push us into deep sleep at the right time and get the highest benefit from hormonal release.
“Midnight” is supposed to roughly mark the middle of our sleeping hours, not our bedtimes.
On the opposite end, waking up too early can rob the brain and body of light and REM sleep, causing diminished benefits of memory consolidation and emotional first aid. Think of what we do to our teenagers who are forced to wake early for school, coupled with the fact that teenagers tend to stay up late.
The timing of wakefulness vs. sleepiness:
Your waking and sleeping states are directed by a couple of very clever systems: the circadian rhythm and sleep pressure.
Circadian rhythm:
You’ve likely heard of the circadian rhythm — the roughly 24-hour clock that resides somewhere in your body. It controls the rhythms of our eating and drinking preferences, mood, and emotional states, the amount we urinate, body temperature, metabolic rate, release of hormones, and more. In addition to making us wake up consistently one minute before our alarm clock and get sleepy in the evening, there isn’t a single organ system or tissue that isn’t regulated in some way by our circadian rhythm. In fact, there isn’t a single organism that has ever been studied that does not abide by the circadian rhythm, from bacteria to trees to animals.
And it’s reset with the most reliable repeating signal in our environment: the sun.
At the intersection where our left and right optic nerves cross each other in the center of our brains, a structure called the “suprachiasmatic nucleus” samples light signals coming in. It uses the signals to calibrate our circadian rhythm every morning, shifting it forward and back through the seasons or when we travel across time zones.
Light from the morning sun reduces melatonin (the hormone responsible for feeling sleepy) in the brain and gives us a little boost of the stress hormone cortisol that informs our brain and body that it’s time to wake up. This morning light exposure from the sun resets our internal clock and gets the body ready for the day, and the reduction in light in the evening allows the brain to begin the process of going to sleep.
The stress hormone cortisol, in its natural abundance and timing, signals our body to increase core body temperature and heart rate, as well as to release stored calories from fat to fuel our first waking hours. At this point in the day, cortisol levels should be at their highest and then steadily decrease throughout the day and night until the following morning. With constant low-grade anxiety or stress, however, cortisol levels can remain high into the evening, either making it difficult for us to fall asleep, or making us wake back up at 3 a.m. and trick our mind into thinking now’s a good time to try to solve all of our life’s problems.
As bright light begins to diminish in the evening and the sky fills with less energetic wavelengths of light — the oranges and reds of the sunset as opposed to the bright white and blue light of midday — the suprachiasmatic nucleus allows for a stronger signal to emerge from melatonin. While not actually a strong sleep hormone like many believe (and not an effective sleep supplement on its own), melatonin is more of a master signaler that informs many other sleep processes to begin. If the signal is weak because of bright artificial lights from screens in the evening, the signal to sleep may be too reduced to effectively get our brain and body to enter the depth and length of the sleep stages discussed earlier.
Sleep pressure:
Sleep pressure is the second system that influences our sleep and wake cycles. As soon as we woke up this morning, the chemical adenosine began to slowly drip into and accumulate in our brains. There, it’s eventually responsible for that irresistible urge to sleep after being awake for 12 to 16 hours.
As it accumulates in the brain, it binds with receptors that begin to turn down the wake-promoting brain regions and turn up the sleep-promoting brain regions. The more it builds up, the stronger the effects, and it doesn’t let up until we give in and fall asleep. At that point, the brain begins to rapidly clear adenosine from the brain to be reset by the morning.
As we’ll learn in this module of the course, caffeine directly disrupts this system by blocking adenosine’s ability to fit into its receptors in the brain, thereby blocking and delaying the effects of sleep pressure. This is why it’s recommended to stop drinking caffeine at least 10 hours before bedtime.
As mentioned previously, our brains and bodies are not simply resting from the day’s efforts while we sleep. Instead, sleep has evolved to be a critical part of our biology, learning, memory, and physical and psychological repair. Our circadian rhythm and sleep pressure work together to move us through the 24-hour cycle and the 90-minute sleep stages during the night.
Here’s to a good night’s rest.
In health,
Coach Mark
Today’s Assignment – Practical Exercise
Bronze – To allow yourself to enter deeper sleep, stop drinking caffeine at least 10 hours before bed. There will be more information on caffeine and this recommendation throughout the module.
Silver – To appropriately spike your cortisol and recalibrate your circadian rhythm, spend 30 minutes outside as soon as you wake up or as soon as the sun rises (if you wake up before the sun or if it’s winter in the Northern Hemisphere). Have your first cup of coffee outside, go for a walk or exercise, meditate, read, anything. Just promise you won’t stare directly at the sun. 😜
Gold – To get a head start on the recommendation in the final lesson of this module, commit to and follow through with a non-negotiable sleep and wake time, also during the weekend. If you could only pick one, make a consistent wake time (within a half-hour window) be your objective. Aim for at least eight hours between bedtime and waking up. Nine hours is even better.
Today’s Exercise
We’re cranking up the intensity today with a sprint workout. If it has been a very long time since you ran any kind of sprint and/or if your body isn’t ready for sprinting in a field or track, you can substitute a row machine or stationary bike.
This one’s simple, but should be performed as intensely as possible. You may want to go to a nearby park or you can simply run out of your driveway and down the street.
Warm up – 10 minutes with high knees and butt kicks. Include a few progressively faster strides across a set distance.
Main set – 15 Good Mornings/hip hinges (doesn’t have to be weighted as the video shows), then launch immediately into a 100-meter (or about 10 seconds) all-out run. Walk back to the start allowing for 90 seconds of rest.
Aim for 5-6 rounds if you’re comfortable with doing sprints. Even 1-2 reps will reap benefits if this is outside your current comfort zone.
Once you can’t sprint with intensity or can’t perform the exercises with proper form, you are done.
Cool down – At least 10 minutes, then stretch.