Why We Sleep: Unlocking the Power of Sleep and Dreams

by Matthew Walker

Sadly, human beings are in fact the only species that will deliberately deprive themselves of sleep without legitimate gain.

Within the brain, sleep enriches a diversity of functions, including our ability to learn, memorize, and make logical decisions and choices.

Downstairs in the body, sleep restocks the armory of our immune system, preventing infection and warding off all manner of sickness. Sleep reforms the body’s metabolic state by fine-tuning the balance of insulin and circulating glucose.

The physical and mental impairments caused by one night of bad sleep dwarf those caused by an equivalent absence of food or exercise.

sleep is the single most effective thing we can do to reset our brain and body health each day—Mother

fact that they did not fall asleep until the early-morning hours. Others (usually morning larks) will chastise night owls on the erroneous assumption that such preferences are a choice, and if they were not so slovenly, they could easily wake up early. However, night owls are not owls by choice. They are bound to a delayed schedule by unavoidable DNA hardwiring. It is not their conscious fault, but rather their genetic fate.

Melatonin simply provides the official instruction to commence

the event of sleep, but does not participate in the sleep race itself.

For every day you are in a different time zone, your suprachiasmatic nucleus can only readjust by about one hour.

Slow rocking increased the depth of deep sleep, boosted the quality of slow brainwaves, and more than doubled the number of sleep spindles.

Post-performance sleep accelerates physical recovery from common inflammation, stimulates muscle repair, and helps restock cellular energy in the form of glucose and glycogen.

Of course, most of us do not play for professional

After being awake for nineteen hours, people who were sleep-deprived were as cognitively impaired as those who were legally drunk.

Operating on less than five hours of sleep, your risk of a car crash increases threefold.

Get behind the wheel of a car when having slept just four hours or less the night before and you are 11.5 times more likely to be involved in a car accident.

A structure located in the left and right sides of the brain, called the amygdala—a key hot spot for triggering strong emotions such as anger and rage, and linked to the fight-or-flight response—showed well over a 60 percent amplification in emotional reactivity in the participants who were sleep-deprived.

When we compared the effectiveness of learning between the two groups, the result was clear: there was a 40 percent deficit in the ability of the sleep-deprived group to cram new facts into the brain (i.e., to make new memories), relative to the group that obtained a full night of sleep.

“It was the students’ choice,” I was told in adamant response emails. “A lack of planned study by irresponsible undergraduates” was another common rebuttal from faculty and administrators attempting to sidestep responsibility.

Right.....blaming 19 year olds. These are Harvard professors?

In other words, if you don’t sleep the very first night after learning, you lose the chance to consolidate those memories, even if you get lots of “catch-up” sleep thereafter.

In the Northern Hemisphere, the switch to daylight savings time in March results in most people losing an hour of sleep opportunity. Should you tabulate millions of daily hospital records, as researchers have done, you discover that this seemingly trivial sleep reduction comes with a frightening spike in heart attacks the following day. Impressively, it works both ways. In the autumn within the Northern Hemisphere, when the clocks move forward and we gain an hour of sleep opportunity time, rates of heart attacks plummet the day after.

South of the brain, we are also discovering that plentiful sleep makes your gut happier. Sleep’s role in redressing the balance of the body’s nervous system, especially its calming of the fight-or-flight sympathetic branch, improves the bacterial community known as your microbiome, which is located in your gut (also known as the enteric nervous system). As we learned about earlier, when you do not get enough sleep, and the body’s stress-related, fight-or-flight nervous system is revved up, this triggers an excess of circulating cortisol that cultivates “bad bacteria” to fester throughout your microbiome. As a result, insufficient sleep will prevent the meaningful absorption of all food nutrients and cause gastrointestinal problems.III

Compared to reading a printed book, reading on an iPad suppressed melatonin release by over 50 percent at night.

First, individuals lost significant amounts of REM sleep following iPad reading. Second, the research subjects felt less rested and sleepier throughout the day following iPad use at night. Third was a lingering aftereffect, with participants suffering a ninety-minute lag in their evening rising melatonin levels for several days after iPad use ceased—almost like a digital hangover effect.