Decoding Sleep
Science is changing the way we think (and dream) about sleep
World Sleep Day was March 19th, at the end of Sleep Awareness Week 2021, so it’s the perfect time to revisit all of the exciting developments in sleep science. I’m also a ‘bad news first’ kind of a gal, so bear with me while I tell you the gloomy parts first. Lack of sleep, sleep apnea, insomnia, shift work and sleep disturbances are a huge medical issue worldwide. In the US alone, 50–70 million individuals have a sleep disorder. There’s plenty of evidence to suggest that we don’t sleep enough (period) and that our sleep cycles are radically disrupted by our environment, phones and other gadgets that we stare at nearly 24/7.
Sleep deprivation impacts our job performance, metabolism, immunity, brain health, etc. And yet, we are really only starting to understand the importance of sleep in our overall wellness. Why is that? I think, in part, it’s because sleep is so mysterious. We don’t really have any true control over when we sleep — we just try to get ourselves in the right state and unconscious brain mechanisms drive the onset of sleep. And unless we set an alarm, we don’t even control when we wake up! What kind of crazy mechanism is this? But, sleep is obviously really really important — since it’s highly conserved across the animal kingdom — but what is it good for?
First — let’s do a quick overview of sleep itself.
“Sleep is a naturally recurring state of mind and body, characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and inhibition of nearly all voluntary muscles during rapid eye movement (REM) sleep, and reduced interactions with surroundings. It is distinguished from wakefulness by a decreased ability to react to stimuli, but more reactive than a coma or disorders of consciousness, with sleep displaying different, active brain patterns.” — Wikipedia
It’s a little outrageous when you think about it — we, and so many others in the animal kingdom lose consciousness, on purpose. If we’ve learned anything about the brain and behavior we know that if something is highly conserved, especially if it puts us in a vulnerable state, it MUST be important for our survival.
Sleep is generally accepted to be composed of four stages.
These stages are categorized by the specific type of activity exhibited by the brain as measured by electroencephalography (EEG). While you might “guess” what state of sleep someone might be in by observing them, EEG is really the gold standard measurement. If you’ve ever been sent to a sleep lab for evaluation, that’s what they are going to use to measure how much of each stage you are experiencing.
REM corresponds to rapid eye movement, and is the state we most closely associate with dreaming. Not only does your brain activity look “awake,” your eyes move while you are dreaming (even though your eyelids are closed). Although dreams can occur in any sleep stage, they are most likely in REM sleep. NREM just simply means non-REM and those stages are characterized by the frequency of brain activity that is observed on the EEG. Each of the stages has an average length, and then the mix of those stages makes up your sleep cycle. Depending on how long you sleep, you will have several cycles during the course of the night.
It could look something like this:
Typically deep sleep happens early to middle in a sleep event and REM sleep is more prevalent later in the night and closer to when we wake up — but any stage can happen at any time during a period of sleep.
You’ll notice from the graphic the type of brain activity, as measured by EEG, that corresponds to each state, with REM being Stage 4 and all of the other stages being NREM — or non-REM. While I’m not trying to be a stickler, EEG really is the standard for measuring sleep stages. Of course our watches, apps, rings and mattresses are doing a good job of tracking our general sleep stages through heart rate, body temperature, actigraphy etc. But they can’t (ever) be as accurate as an EEG. I still wear a ring to track my sleep, it’s very convenient. I just know it’s an approximation.
The Sleep Foundation has a nice explanation of sleep stages. Of course the question is what are all of the stages for? Why isn’t it just one uniform unconscious state? We haven’t decoded that mystery yet — but researchers have found that deep sleep (stage 3) and REM sleep are separate but both critical for brain function in different ways. Deep sleep is thought to be restorative for the brain, maybe even cleaning out the accumulated “residue” in the brain. One puzzling element is that we generally experience LESS deep sleep as we age, seemingly when we might need it most to help “clean up” our aging brains. Also deep sleep is highly susceptible to our environment and behaviors, like exercise, eating too close to bedtime and drinking alcohol before bed (a night cap isn’t a good thing for your sleep!) More on deep sleep a little later.
REM sleep is highly correlated with memory, learning and maybe even creativity. Of course, like so many things in sleep, we don’t control the narrative and content of our dreams either. Hence Hamlet’s concerns about eternal sleep!
“To sleep, perchance to dream, ay there’s the rub” — Hamlet, Wm. Shakespeare
Certainly the intensity of vivid dreaming seems to make sense in the context of those elements. It’s the best explanation that I’ve heard for why we dream, but there’s so much more to learn. Later I will describe work that is ongoing to start working with these sleep stages for some exciting benefits.
Before I get to modifying and enhancing sleep, there’s a big topic I haven’t addressed directly yet: Why do we sleep? Or maybe even why do animals sleep, forget about just humans! There is no one answer and theories abound. I like this list from Harvard that covers some of the plausible reasons. There’s even a popular book out called “Why We Sleep?” — clearly we are curious about this state we spend so much of our lives in! While there’s no definitive answer, we know that quality sleep benefits brain health, brain function, metabolism, immunity and a host of other body functions. With a clear evolutionary conservation of sleep in mammals in particular, we can rest assured that it’s important for more than we can understand right now. It’s a critical part of long term health and wellness.
Unfortunately, sleep deprivation is common in our modern society. Stress, caffeine and lights/devices overstimulate our nervous systems and disrupt our sleep cycles. You may have heard of the term “sleep hygiene.” It doesn’t mean being clean before bed! It’s really about developing good sleep habits that you practice with consistency. The brain LOVES patterns and consistency. It’s why part of good sleep hygiene is trying to go to bed at the same time every night and wake up at the same time in the morning. If you have a regular sleep pattern during the week but then stay up too late on the weekend, you are disrupting your circadian rhythm and your overall sleep quality will suffer.
One key element of sleep hygiene is sleeping in as dark of a room as possible. Blackout shades and/or an eye mask are one way to help remove excess light from your bedroom. As many experts have said, try to keep the bedroom for sleep and bedroom related activities! No laptops, TV’s, phones — especially late in the evening. We live in a constantly illuminated world (think of a Las Vegas casino!) and this constant light is extremely confusing to the clock inside our brain that tells us when to sleep and when to wake up. The more light we take in, especially late in the evening, the more confused our brains become about when to sleep. So make it dark!
Another trick is to make it cool. Body temperature naturally drops during sleep and having either the entire bedroom or the mattress itself cool can help the body move into the deeper more restorative stages of sleep. While a cold bedroom isn’t for everyone (although Tom Brady swears by it), you can get the same effect with a cooling mattress pad and not freezing out your partner. If you are a particularly “hot sleeper” it might be worth a try to see if it leads to deeper sleep.
Maybe you are one of those folks who says, oh I don’t need that much sleep, this is irrelevant for me! While there are documented cases of “familial natural short sleepers” — those with a genetic mutation that leaves them functional with 4–6 hours of sleep — it’s only 1% of the population. Which means that if you are sleeping 6 hours or less a night, you likely aren’t a part of this special group, you are sleep deprived! Adult humans need 7–8 hours of sleep, consistently, to maintain brain health and overall performance without excessive daytime sleepiness and the need for stimulants (like coffee).
Another sleep challenge in our society is shift work. It’s estimated that around 16% of working adults have some type of shift-based work that often has them working late into the night or even overnight. While these roles may be necessary, the disruptions to sleep cycles are profound and there is some thought that long-term shift work can lead to earlier progression of some diseases. Even worse is “random” shift work, where the body doesn’t get to develop a pattern. It’s like daylight savings time every day in terms of disruption. (Don’t get me started on daylight savings time…) The military is finally waking up to these issues. After decades of using an 18 hour day on submarines (remember there’s no natural light on a submarine), the US Navy implemented a shift to a 24 hour day to better match circadian rhythms and natural sleep cycles in 2014. The Navy followed in 2017 with changes to the surface fleet as well. The reported results were incredible, not just on morale but on mission execution and readiness. Remember, sleep deprivation isn’t just something you “tough out” even if you are in the military — sleep deprivation can have the same impact as being impaired by alcohol in terms of mental performance and reaction time.
At DARPA, I managed a program called Preventing Sleep Deprivation where we were able to study sleep deprivation in humans and think about how other animals manage sleep. Through this work we looked at the sleep cycles of other animals that are able to demonstrate continuous performance (think migrating birds and dolphins) and start thinking about how to modulate the human brain to overcome these challenges. Of course, these questions were extremely relevant to the military — since continuous performance is often a requirement of that work. We learned some pretty exciting things, both about humans and animals. Did you know that dolphins are able to put separate hemispheres of their brains to sleep in an alternating way so that they can keep swimming? Amazing. It appears that they can do this because they have a degree of hemispheric separation that is NOT seen in human brains (too bad!)
Since we couldn’t figure out how to pull off that dolphin trick, we started looking at ways of enhancing shorter sleep bouts, like naps, or specifically trying to enhance slow wave sleep. One of the researchers on the program, Dr. Giulio Tononi showed that he could use transcranial magnetic stimulation (TMS) to enhance slow wave sleep while individuals were already asleep in the lab. This work showed that slow wave stimulation could enhance cortical plasticity, which is critical for long term learning in the brain. This was an example of closed-loop stimulation — EEG was used to measure the stage of sleep that an individual was in and then stimulation was applied to enhance that particular phase. If you recall, slow wave sleep is thought to be the most restorative stage of sleep — so figuring out a way to enhance or extend this stage was really exciting. Of course a TMS machine is a big clinical instrument and a little bulky. Dr. Tononi then suggested that other types of stimuli could potentially have slow wave enhancing effects, like transcranial direct current stimulation (tDCS) and auditory stimuli. For a refresher on neuromodulation, see my previous blog post! This is a breakthrough in its elegance. Instead of a more complex clinical research tool — impacts on slow wave sleep can be seen with something as simple as auditory stimulation during slow wave stages.
As part of the US government’s BRAIN Initiative, DARPA began a program in 2015 called RAM Replay. It leveraged the idea that when encoding new memories, the brain replays the memory during sleep, hence the “replay” in the title. Benefitting from the earlier work of researchers in the field, like Dr. Tononi, those funded by the program eventually demonstrated that indeed memories could be enhanced by stimulation of the brain during sleep, using both auditory and electrical approaches. Because of the universal nature of sleep, these solutions are not just for the military, despite their original funding.
Because of advances in electronics and wearables, EEG headsets to monitor sleep stages (recall it’s the gold standard!) are not just the domain of researchers and elite warfighters. Consumers now have access to these technologies through commercial paths. Companies like Dreem, Philips Smart Sleep and Sleep Shepherd now sell headsets with integrated EEG for sleep monitoring and closed loop auditory stimulation matched to sleep staging for enhancement. I have a feeling this area is just getting started in terms of it’s impact to sleep. Sleep is definitely one area where neurotechnology is making the biggest inroads and impact.
In terms of future research, I believe that we will continue to uncover the mysteries of human sleep. By using the tools both at our disposal and in development, we will not only figure out how to enhance sleep but maybe control it altogether. I’m envisioning our science fiction future, where on our trips across the solar system we can enter hibernation to make the trip seem shorter and download new skills through our dreams on the way. If you’re as fascinated by sleep as I am, please join us for a Webinar on Decoding Sleep on April 14th at 3pm ET. Sign up here. Until then, sweet dreams!
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