UC Berkeley neuroscientist Matthew Walker thinks so. Biologically mandated to support our survival for centuries, sleep is being short changed. And the health consequences are staggering. In short, our sleep deficit can shorten our waking lives.
I’ve read so many articles on improving sleep and you probably have too. But what I’ve learned from reading and re-reading Walker’s book, Why We Sleep and listening to Stanford vision scientist Andrew Huberman’s many podcasts on leveraging better sleep is different.
If good sleep eludes you or you are just curious about why sleep tops the list of life-extending practices, then I invite you to read this two-part blog. This post focuses on the science of sleep. The next one will concentrate on practical tips based on science.
There are two factors that cause being awake and asleep – our 24- hour circadian rhythm and sleep pressure.
First, picture a tiny internal 24-hour clock in the middle of the brain. Called the suprachiasmatic nucleus, it receives light signals from each eye down the optic nerves to the back of the brain for visual processing. This light information maintains the 24-hour cycle, our circadian rhythm.
Second, with every waking minute the chemical adenosine accumulates in the brain. As adenosine rises so does our desire to sleep. This sleep pressures builds typically over 12 -16 hours from waking at which time the urge to sleep is hard to resist.
But resist it does when caffeine is in the system. Caffeine competes with adenosine for the same brain receptors, which is why it keeps us awake. More startling is how long caffeine stays in the system, from 8 – 12 hours.
As the day ends, the brain’s internal clock uses the hormone messenger melatonin to blare “it’s night” to the brain and body. “Runners take your mark.” Melatonin propels you to the starting line of sleep, but doesn’t influence how you run the race, i.e., sleep through the night.
Once we have heeded the message from melatonin and yielded to the sleep pressure of adenosine, we head off to bed or drop asleep on the sofa. Then, what happens?
The architecture of sleep is fascinating. Basically, two stages of sleep, non-rapid eye movement (NREM) and rapid eye movement (REM), play a tug of war over which stage will prevail. This back-and-forth tussle replays throughout the night in 90-minute cycles. While these stages continue to take turns, so to speak, the duration of each changes. NREM sleep dominates in the first half of sleep; REM sleep intensifies in the second half of the night.
Think of the slow wave, synchronized pattern of NREM sleep as a file processing center. New files, i.e., recent experiences, are moved from a temporary short-term storage site to a more secure long-term storage location. During this deep sleep, the brain is culling what is unimportant to remember and fortifying the neural connections to new facts and perceptions. Walker calls NREM sleep a state of internal reflection following the state of reception characterizing wakefulness.
What about REM sleep? Curiously REM sleep resembles wakefulness in terms of faster-frequency, uncoordinated brainwaves. But you’re sound asleep and the telltale sign is that your voluntary muscular tone is absent; you are paralyzed. However, the brain centers for vision, hearing, and sensing are furiously associating past experiences with new input with the range of sights, sounds, and emotions that can lead to some crazy dreams. Walker calls REM the stage of integration when the brain is trying to figure out how the world works and what is your place in it. And this is the stage of sleep when new learning, for example, chemistry formulas for a test the next day, takes hold. And alcohol impairs this REM sleep sedating the brain with the appearance of good sleep when, in fact, it disrupts REM activity.
Here's what to keep in mind from this quick tour of the brain awake and asleep. It's a brilliant system. Light sets our internal clock. The pressure to sleep begins to build from the time we awake until about 12 - 16 hours later when the urge to sleep overpowers our wakefulness. Melatonin adds to this potent mixture to signal it's time for this sleep event to begin. Then, the brain engages in this cycling dance of NREM and REM sleep - both crucial to memory consolidation and integration. What could go wrong and how can we sleep better? Next time.