Entrepreneur and researcher Dan Pardi delves deep into the need for sleep in this first instalment of his three-part series.
As a sleep researcher and sleep educator, the most common question I get is, “How do I know how much sleep I need?” This question is harder to answer than you might think, because the benefits of sleep are only partially determined by sleep duration, and sleep needs vary on an individual basis.
When people ask this question, what they really mean is, “What are the things I need to do in order for me to get all the benefits of a perfectly managed sleep-wake practice?” After reading this article series, you will be better equipped to answer this question.
To begin, we need to quickly review the fundamentals of sleep and wake regulation. This will help you understand how sleep is triggered by the nervous system and what you need to do to promote it.
We still don’t fully understand the purpose of sleep (which is part of what makes it so fascinating to study!). However, we do know that many important things take place during the period of time between when you shut your eyes at night, and when you open them again in the morning.
A major breakthrough in the field of sleep research took place in 1982, when Dr. Alexander Borbely, Professor Emeritus at the University of Zürich, published an article in the journal Human Neurobiology describing a concept of how sleep and wake are controlled over a 24-hour period. He dubbed his idea the 2-Process Model of Sleep Regulation. This model changed the way the world understood how sleep and wake are regulated.
In Dr. Borbely’s model, he explained that the control of these states is based primarily upon the combination of two different processes occurring simultaneously. To understand how to get the sleep you need, let’s explore those processes. First, we’ll address sleep pressure.
The first process of the professor’s 2-Process Model is sleep pressure.
From the moment you wake up in the morning, sleep-inducing substances start to accumulate in the brain. This produces a need for sleep that rises continuously throughout the day, sort of like sand collecting at the bottom of an hourglass. It works pretty much exactly like you would expect: the longer that you are awake, the more intense the need for sleep becomes.
This built-up sleep pressure helps you 1) fall asleep, and 2) stay asleep until the next morning. When you go to sleep, this pressure decreases, and after a night of complete sleep, you start the next day with low sleep pressure. From there, the process starts all over again. When you fail to wear down all of this sleep pressure before starting the next day, you experience a phenomenon known as “sleep debt,” which I will explain later.
But wait. If sleep pressure keeps growing from morning to night, why don’t we become increasingly sleepy from the moment we wake up? That’s where the second process of the 2-Process Model comes into play.
While sleep pressure rises from morning to night, this is countered by wake drive, which also builds from morning to night. Wake drive is an outcome of multiple brain systems working together to produce an alerting signal. This signal increases in intensity to curb the effects of mounting sleep pressure.
The result? Your alertness stays relatively even across the day (with some within-day fluctuations). This is why you don’t get increasingly sleepy from the time that you wake up.
But this raises another question: If wake drive is high during the night, how do we fall asleep? To understand the answer, we need to discuss how sleep pressure and wake drive differ from each other.
Unlike sleep pressure, which is determined by time awake and time asleep, wake drive is controlled by a 24-hour rhythm, like an oscillating sine wave (a repeating wave-pattern with a high point and a low point).
The dotted line indicates the greatest distance between sleep pressure and wake drive. It’s the time you feel the greatest urge to sleep.
For instance, let’s assume that someone typically wakes up at 7am and goes to bed at 11pm, and that his or her wake rhythm is stable and fixed to this time frame. Under these conditions, their wake drive initiates at 7am, builds all day to counteract mounting sleep pressure, reaches its peak at 10pm, and plummets at 11pm, descending to its lowest point across a 24-hour period. At 7am the next morning, it begins to build back up all over again.
This rhythm repeats day after day – you awake at the same time and feel sleepy at the same time, on a daily basis. And the timing of the rhythm can be shifted forward or backwards.
Let’s briefly explore what sets the timing of our daily wake rhythm.
Imagine you live in San Francisco, and travel halfway around the globe to Rome, Italy. When you arrive, your internal rhythms are still synced to San Francisco. At the beginning of your trip, you’re awake at night when everyone in Italy is sleeping, and sleepy during the day when everyone else is fully awake. But slowly your body starts to adjust to this new time zone.
So, how does the body “know” to shift the timing of its internal rhythms to be in sync with the environment? In the next article in this series, I’ll explain what signals the body relies upon to coordinate the timing of your wake rhythm, and what happens when this signal goes awry (something that is becoming ever more common in the modern world). We’ll also look at some things that you can do to optimize this rhythm. More to come!
Dan Pardi is an entrepreneur and researcher whose life’s work is centered on how to facilitate healthy behaviors in others. He does research with the Psychiatry and Behavioral Sciences Department at Stanford, as well as the Departments of Neurology and Endocrinology at Leiden University in the Netherlands. His current research looks at how sleep influences decision-making.
He is also the CEO of humanOS.me (formerly known as Dan’s Plan), a health technology company that utilizes the Loop Model to Sustain Health Behaviors – which he developed – to help people live a healthy lifestyle in a modern world.
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