As a result of advancing technologies in science and engineering, we can study the brain in real-time from many different angles. We can study the strength and intensity of connections between different brain areas as well as the inner-workings of individual nerve cells. These advancements led to discoveries across neuroscience but, in particular, for understanding how and why we sleep.
Functions of Sleep
To date, there is no single universal function for sleep. For centuries, rest has been deemed essential for physical and mental rejuvenation and a defensive mechanism against mental illness.
With advancing technology, we now know that the extent of physical rejuvenation through sleep includes muscle repair and growth and the replenishment of sugars and fats through the release of anabolic hormones at night. We know sleep helps mental rejuvenation by clearing metabolic waste, including those linked to neurodegenerative diseases such as Alzheimer's.
Sleep also improves the ability to learn and recall information from one day to the next, and even the preservation of basic (reaction time) and complex (arithmetic) mental tasks.
Getting Adequate Sleep
Even if we do know and discover more functions of sleep, how do we know that someone has gotten adequate sleep, and how do we test if they are functional?
To address the first question, we have to dissect what we know about how much sleep the average human needs. In high-performing populations, it is a commonplace to hear, "I can get by on 6 hours a night." Sleeping less is seen as a badge of honor by many of our nation's leaders and top business professionals (except for Arianna Huffington).
In reality, most humans need 8 hours of sleep a night. We know this from very large-scale studies involving thousands of individuals just from asking one or a few questions along the lines of, "how much sleep do you need to feel rested the next day without relying on stimulants or napping to get by." So if a Silicon Valley executive answers "6," but this "6" includes 4-5 shots of espresso at once and/or multiple times a day, then he/she is lying and only hurting themselves physically and mentally in the long term.
We can also test how much sleep someone needs to function through very simple quantitative tests first developed in military science and academic laboratories.
These tests include the psychomotor vigilance test or PVT for short. The PVT is designed to measure your ability to maintain high levels of attention to a target presented at random time intervals on a screen.
When individuals are not achieving their highest levels of sleep, they will miss the presented target entirely or have a false start. Years of careful study between hours awake and performance on the PVT have revealed direct negative correlations between performance and sleep needs; there's usually a drop off in performance with less than six hours of sleep the night before.
Further, the only way to get performance on the PVT back to rested levels is through paying back sleep lost. Over time with inadequate sleep, though, it becomes harder and harder to pay back lost sleep, resulting in an overall sleep deficit that can take years off one's life and contribute to poor health outcomes.
So how do these laboratory tests look in the real world when people have insufficient sleep? The most straightforward test is how likely are you to feel sleepy and/or fall asleep while doing something such as driving a car, being stopped at a red light, reading a book, or watching TV. If the answer is "yes" to the first two, you need to re-evaluate life priorities and get sleep before someone else's life is at risk. If the answer is "yes" to the second two, then a good week or two of going to bed one hour earlier should help to repay that sleep debt. A one percent change in sleep habits can lead to a 50-60 gain in performance, and this is something, especially those in data-driven industries who ironically get less sleep, ought to appreciate.
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