“It’s 2 a.m.and you’re lying in bed. You have something immensely challenging to do-a critical meeting, a presentation. You have to get a decent night’s rest, but you’re still wide awake. You try different strategies for relaxing-take deep, slow breaths; try to imagine restful mountain scenery–but instead you keep thinking that unless you fall asleep in the next minute, your career is finished. Thus you lie there, tenser by the second. Now other stressors creep into your mind: money worries, deadlines, the fact that you’re not asleep.
“All this is typical speciocentric human thinking. Zebras, by contrast, don’t think this way. If you want a good night’s sleep, think more like a zebra or a walrus. For the vast majority of beasts on this planet, the most upsetting things in life are acute physical crises. You are that zebra, a lion has just leaped out and ripped open your stomach, you’ve managed to get away, and now you have to spend the next hour evading the lion as it stalks you. (Now, that’s stress.) As a zebra, your body’s physiological response mechanisms are superbly adapted for dealing with a short-term physical emergency such as this-after which either it’s over with or you’re over with. But when we human beasts lie around and worry about stressful things like work and mortgages, we turn on the same physiological responses that make us poised to fight or flee. And that’s not an ideal state of mind or body to be in when you want to get some sleep. To understand how stress can turn into the beast that ate Slumberville, and do something about it, you need to understand your brain when it sleeps.
To start, sleep is not a monolithic process. Instead, there are different types of sleep: shallow sleep (stages 1 and 2), during which you are easily awakened. Deep sleep (stages 3 and 4, or “slow-wave sleep”). REM sleep, in which your eyes dart around and dreams happen. There are not only these different stages but also a structure, an architecture to them. You start off shallow; gradually sleep your way down to slow-wave sleep, followed by REM, then back up again; and then repeat the whole cycle about every 90 minutes.
Not surprisingly, the brain works differently in different stages of sleep. This can be studied by having people sleep in a brain scanner while you measure the levels of activity of different brain regions.
The picture during slow-wave sleep makes lots of sense. Parts of the brain associated with arousal activity slow down. Ditto for brain regions involved in controlling muscle movement. The areas of the brain that first respond to sensory information have somewhat of a metabolic shutdown. What you’ve got is a metabolically quiescent, sleeping brain. And this is logical, as deep slow-wave sleep is when energy restoration occurs.
A very different picture emerges during REM sleep. Overall, there’s an increase in activity. Some brain regions become even more metabolically active than they are when you are awake. Parts of the brain that regulate muscle movement, brain-stem regions that control breathing and heart rate-all increase their metabolic rate. In a part of the brain called the limbic system, which is involved in emotion, there is an increase as well. The same for areas involved in memory and sensation.
So those are the nuts and bolts of sleep. Entrée stress.
No Sleep, More Stress
As we glide down into slow-wave sleep, the sympathetic nervous system, which keeps us “wired,” relinquishes control to the parasympathetic nervous system, producing a calm, vegetative state. This calming effect is reinforced by a decrease in levels of glucocorticoid, or brain fuel.
During REM sleep, as you’re mobilizing energy to generate that outlandish dream imagery and to move your eyes rapidly, glucocorticoid secretion and the sympathetic nervous system rev up again. But given that slow-wave stages make up most of what counts as a good night’s rest, sleep is predominantly a time when the stress response is turned off. This is true for all animal species, whether they’re nocturnal or diurnal (that is, sleeping during the dark hours, like us). About an hour before you wake up, levels of certain “wake-up hormones” and glucocorticoids begin to rise. This is not just because merely rousing from slumber is a mini-stressor, requiring mobilization of some energy, but because those rising stress-hormone levels play a role in terminating sleep.
If you deprive yourself of sleep, the sleep-induced decline in the levels of those stress hormones has no chance to occur. Instead, glucocorticoid levels increase and the sympathetic nervous system is activated. The elevated glucocorticoid levels during sleep deprivation play a role in breaking down some of the stored forms of energy in the brain. This could have something to do with why learning and memory are so lousy when you’re sleep-deprived. That’s something we all learned when doing an all-nighter and discovering the next morning during the final exam that we could barely recall what month it was, let alone any of the factoids crammed in our heads the previous night.
A recent study beautifully demonstrated one way in which our brains become impaired when we try to think hard after we haven’t slept. Take a rested subject, stick her in a brain imager, and ask her to add sequences of three-digit numbers, and her frontal cortex lights up metabolically. Take someone who is sleep deprived and give him the same math exercise, and he does awful at it. What does his brain look like? You might have expected that his frontal cortex would be inhibited-too groggy to compute. Actually, the opposite occurs: The frontal cortex is activated, but so are large parts of the rest of the cortex. It’s as if sleep deprivation has reduced this gleaming computer of a frontal cortex to a bunch of unshaven gibbering neurons counting on their toes, having to ask the rest of their cortical buddies to help out with this tough math problem.
So why care if sleep deprivation is a stressor? We’re accustomed to all sorts of amenities in our modern lives: overnight deliveries of packages, advice nurses who can be called at 2 a.m., round-the-clock technical-support staff. All of these services are performed by people who must work under conditions of sleep deprivation. We’re not a nocturnal species, and if a person works at night or works swing shifts, regardless of how many total hours of sleep he’s getting, it’s going against his biological nature. People who work those sorts of hours tend to overactivate the stress response. It’s not surprising then that night work or shift work increases the risk of cardiovascular disease, gastrointestinal disorders, immune suppression, and fertility problems.
These worries about sleep deprivation are relevant even to those whose 9-to-5 job is 9 to 5 during daylight hours. An unprecedented number of other social and environmental factors-including noise pollution and the exponential growth of indoor lighting-seem to conspire to deprive us of sleep. In 1910, the average American slept 9 hours a night, disturbed only by the occasional Model T back-firing. We now average 7.5, and that’s declining. When there’s the lure of 24-hour-a-day fun, activities, and entertainment or, for the workaholic, the knowledge that somewhere, in some time zone, someone else is working while you indulge yourself in sleep, that pull of “just a few more minutes” of pushing yourself becomes irresistible. And damaging.
More Stress, No Sleep
What should happen to sleep during stress? This one’s simple, from a zebra-centric point of view: lion coming, don’t nap. (Or, as the joke goes, “The lion and the lamb shall lie down together. But the lamb won’t get much sleep.”) The hormone CRH seems to be most responsible for this effect. This hormone not only starts the glucocorticoid cascade by stimulating the release of another hormone called ACTH from the pituitary, but it’s also the neurotransmitter that activates fear, anxiety, and arousal pathways in the brain. Infuse CRH into a sleeping rat’s brain, and you disturb sleep-it’s like throwing ice water onto those happily dozing neurons. Not surprisingly, about three out of four cases of insomnia are triggered by a major stressor. Moreover, many studies show that poor sleepers tend to have higher levels of sympathetic arousal or of glucocorticoids in their bloodstream.
Maximum stress can do more than minimize sleep; it can compromise the quality of the sleep you manage to get. CRH infusion, for example, decreases the total amount of sleep mainly by decreasing slow-wave sleep, exactly the type you need for energy restoration. Instead, your sleep cycle is dominated by shallow-sleep stages, meaning you wake up more easily-fragmented sleep. And even the slow-wave sleep you do get could be disrupted. Ideal slow-wave sleep shows a characteristic pattern in what is called the “delta power range,” which can be detected on an electroencephalogram (EEG) recording. When you are stressed presleep, or are infused with glucocorticoids during sleep, you get less of that helpful sleep pattern during slow-wave sleep.
Stress Causes Insomnia Causes Stress Causes…
We have the potential for some real problems here, as lack of sleep or poor-quality sleep activates the stress response and an activated stress response makes for less sleep or lower-quality sleep. Each feeds on the other.
As one fascinating study suggests, simply the expectation that you’re going to sleep poorly makes you stressed enough to get poor-quality sleep. In the study, one group of volunteers was allowed to sleep for as long as they wanted, which turned out to be until around 9 a.m. As would be expected, their stress-hormone levels began to rise around 8. How might you interpret that? These folks had had enough sleep by about 8 a.m. and their brains-happily restored and reenergized-knew it. They started secreting those stress hormones to prepare to end the sleep.
Now, the second group of volunteers went to sleep at the same time as the first but were told that they would be woken up at 6 a.m. And what happened with them? At 5 a.m., their stress-hormone levels also began to rise.
This is important. Did their stress hormones kick in 3 hours earlier than those of the other group because they needed 3 fewer hours of sleep? No. The rise was due to the stressfulness of anticipating being woken up earlier than desirable. Their brains were feeling that anticipatory stress while sleeping, demonstrating that a sleeping brain is still a working brain.
Thus, there is a hierarchy when it comes to miserable sleep. Too little continuous, uninterrupted sleep-deadline looming, go to sleep late, get up early-is not good. Even worse is too little sleep that is unpredictably fragmented. You go to sleep with the corrosive knowledge that 5 hours or 5 minutes from now, a patient will come into the emergency room, or the alarm will go off and it’s back to the fire truck, or someone’s diaper will slowly but surely fill up and trigger bloodcurdling screams.
This teaches us a lot about what counts as good sleep and how stress can prevent it. When it comes to what makes for psychological stress, a lack of predictability and control in your life are at the top of the list of things you want to avoid. Here are the 32 Secrets of A Stress-Proof Life.
For more advice on living your best life, follow us on Facebook now!