"Sleep is the best meditation." - The Dalai Lama
Sleep is a risky behavior, one that defies common sense. Although the need for sleep is widespread across the animal kingdom, it runs counter to our hard-wired drive for survival. From the most complex creatures such as humans, primates, octopus, and dolphins, to simple species such as jellyfish and nematode worms, it seems any lifeform that has a nervous system has a need for sleep, a need so strong that it overrides an organism’s basic need to keep itself out of harm’s way.
We may not know exactly why we sleep, but we know how to define it. Sleep is not just inactivity; it is a special kind of inertia in which we are not comatose—we can be roused from sleep--but are in a special type of unconscious state. Scientists have known for some time that the brain cycles through different stages during sleep, with each stage lasting a certain amount of time and characterized by different brain wave patterns. The first stages of sleep last about an hour and are characterized by a light sleep, one in which we can be easily woken. These stages seem to help us transition into sleep’s deeper stages where the important work of repair takes place. The third and fourth stages are characterized by slow brain waves, a deep sleep in which it is hard to rouse someone. From these stages we transition into REM sleep, the stage that involves rapid eye movement, where dreaming takes place. The architecture of sleep is far from a state of inactivity; during sleep we oscillate between a deep state of slow brain waves to the dreams of REM. Whereas we cycle through REM sleep continuously, by the fifth or sixth hour we spend less time in deep sleep, gradually coming back to the lighter sleep of stage one and two before we wake up.
Although our understanding about what happens during the stages of sleep continues to evolve, we know that each stage plays a distinct role in restoring the brain’s functioning. Evidence suggests that the process of cycling between stages is also important. Spending an inadequate amount of time in either the slow wave or REM stages will result in a poorer quality of sleep, even if we get eight or more hours a night.
During slow wave sleep, the cerebral spinal fluid channels open and flush the brain, essentially rinsing away metabolic wastes that have built up, carrying them to the liver where they are processed and discarded. This “brain washing” can only happen during sleep; it does not happen when we are awake and aware. Flushing the brain with fluids is an essential part of the brain’s repair process, as synapses expand as much as 60 percent, helping clear the brain of toxic metabolites and proteins. This may be why chronic sleep deprivation is associated with an increased risk of dementia and Alzheimer’s disease, as lack of slow wave sleep allows amyloid proteins to build up in the brain.
Other important repair processes take place during slow wave sleep, including the process of memory consolidation. Have you noticed how your memory recall is so muddled when you are sleep deprived? During slow wave sleep, our daily experiences, including what we have learned and the information we collect, are processed and organized, taken out of the short-term storage area of the hippocampus and transported to the long-term memory centers in the brain. Synapses are pruned during this stage, refreshing them so they are primed and ready for future activation. We can think of slow wave sleep as a time when the maintenance crew comes in to clean up the detritus from the day, gather and organize the day’s information and memories, and trims our synapses so we are ready to learn new things upon waking.
We know less about REM sleep, but evidence suggests that the dreams associated with this stage play a role in processing emotions and building resilience to distressing situations. Activity in the amygdala, the area of the brain associated with fear, decreases during REM sleep, allowing us to revisit events without initiating a stress response. Although we cycle through REM stages of sleep throughout the night, the most intense REM activity occurs in the final two hours of sleep. Recent research shows that when people don’t get enough sleep, they are more likely to experience higher levels of amygdala activation when exposed to negative situations. These findings are not surprising—most of us know that we’re more likely to feel overly stressed when we are tired and sleep deprived.
There is growing evidence of a strong relationship between sleep, depression, and anxiety. It was once thought that poor sleep was a symptom of these conditions, but sleep disturbances are now thought to be a significant contributor to the development of depression and anxiety; up to 84% of depressed people report poor sleep and those with insomnia are over 17 times more likely to report high levels of anxiety. Sleep issues frequently occur prior to the mood changes associated with depression, with depressed individuals showing shifts in their sleep architecture. People who are more likely to be depressed may take longer to fall asleep, wake more often during the night, and spend more time in REM sleep. With reduced time in deep sleep, they miss the important brain flushing and maintenance functions that occur during slow wave sleep, leaving them more vulnerable to developing or worsening depressive symptoms.
If sleep is so important for our health, why do so many of us fail to get enough? There is no shortage of reasons why so many are sleep deprived, from artificial light, when and what we eat, a lack of exercise, alcohol or caffeine consumption, and the newest villain—social media. Although all these factors can impede our slumber, by far the real enemy of sleep is a lack of routine. Most sleep specialists agree that having a routine is critical to being able to get a restful and beneficial night’s sleep. But “routine” means much more than simply going to bed at the same time every night. Good sleep hygiene starts the moment we start our day. Just as the quality of your sleep determines how well we function during the day, what we do during the day strongly influences how well we sleep.
Humans evolved in environments devoid of artificial light, so our physiology is wired to be in sync with natural light; our bodily processes are wired to be more active during the day and slower as nighttime approaches to prepare us for sleep. These cycles of activity and rest are regulated by an internal master clock called the suprachiasmatic nuclei (SCN), located deep within the hypothalamus. Specialized cells in the retina that are sensitive to light relay information to the SCN which then initiates changes in the body, such as the production of melatonin, a hormone that promotes sleepiness, which increases as the sun starts to set and decreases when it is light. Provided we are healthy, the body initiates hormones that keep our energy levels high during daylight hours, peaking in the late morning and early afternoon when the sun is at its highest point in the sky, and then shifts to hormones that start to slow our bodily processes down as we approach night.
Our daily routines will invite restful sleep when they are synchronized with the natural rhythms of light and dark. Daily activities set us up for sleep when they are appropriately synchronized with the sun. Distracting and noisy environments as well as analytical, problem solving, or high energy activities are best tackled at the heart of the day when there is abundant sunlight. Daytime is when we have the energy to handle distractions, restlessness, change, and lots of movement; that is the time when our bodies are primed to keep us alert and active.
As the sun heads toward the horizon, our physiology is designed to make a slow transition that prepares us for the work of sleep. With waning light, hormones start to shift and energy wanes, encouraging us to transition to calmer, quieter activities. But nature no longer controls our exposure to light, we decide when the day ends, and rather than a slow transition, it comes with a flick of a switch. Our bodies do not know the difference between natural and artificial light, which forces us to remain in daytime mode, encouraging us to maintain a distracted, noisy, agitated state that is fueled by scanning social media, checking email, or flitting between streaming shows. Is it any wonder we can’t transition to sleep once the light is turned off, or that we wake up at 2 am and can’t fall back to sleep? Artificial light allows us to hack our natural rhythms and engage in activities that were once reserved for the middle of the day. To prepare for sleep we must take the time to purposefully downshift our energy, transitioning to evening activities that will help us drift into a restorative slumber.
Sleep is critical to our health; there is a reason why sleep deprivation is a form of torture. As our understanding of what happens during sleep grows so does our understanding of the serious downstream health consequences of interrupted or insufficient sleep. Even so, sleep scientists warn of the dangers of worrying about whether we are getting enough sleep; “problematizing” sleep can put us into a tailspin. They remind us that most of the things we need to do to get more sleep are obvious: synchronize our lives with natural light, slow down in the evenings, limit our caffeine and alcohol, exercise daily, and eat a healthy diet. They also remind us that a few days or even a week of poor sleep from time to time is not a catastrophe, as everyone has periods of sleeplessness. However, persistent insomnia or poor sleeping patterns call for medical attention and should be taken seriously.
We are at the start of the summer season when the sun sets later, and we tend to stay active well beyond the peak of the day’s light. We need to be a bit more conscientious about the day’s activities to help us prepare for sleep. This week I invite you to notice how you make the transition from the busy, distractable, high-energy pulse of daytime to the quieter, calmer activities as the light of day starts to wane. What types of activities encourage a smooth transition to a restful sleep for you? Evening is the time for us to let go, to make space for the work of sleep. How do you let go of the day and invite in the night?