The biological pressure to sleep cannot be resisted
After about 16 hours of nonstop wakefulness, we normally feel a biological pressure to sleep. This pressure, known as the homeostatic sleep drive, is controlled by a separate neurological regulatory mechanism in addition to the biological clock.
This regulatory mechanism is keyed by a pinhead-size cluster of brain cells known as the ventrolateral preoptic nucleus, or VLPO. The VLPO is sensitive to a chemical naturally produced in the brain known as adenosine, one of several neurotransmitters involved with our daily sleep-wake cycle. After about 16 hours of adenosine build-up, the VLPO sends out a signal that it’s time to sleep.
In this way, the brain essentially keeps track of how long it is awake, and after about 16 hours reinforces the circadian rhythm to induce sleepiness. For optimal sleep, it’s therefore important the two processes – sleep drive and the biological clock – are synchronized and working together. Later in the STS, you will learn how to enhance this mutually supportive process for maximum benefit.
As we age, the VLPO typically loses some of its neurons, and thus some of its ability to drive sleep. This is one reason why as we age we tend to experience lighter, more fragmented sleep. So some diminishment of the VLPO is therefore a normal consequence of aging, and this helps explain why the elderly often sleep less than younger adults.
To counter this natural age-related reduction of the VLPO, there are a number of simple, effective, completely drug-free methods you can employ to strengthen and in effect rev up your sleep drive. We will cover this in the first week of the STS.
Interestingly, caffeine apparently disrupts the neurological homeostatic sleep drive by blocking the VLPO’s ability to recognize adenosine. So in addition to being a metabolic stimulant, this is another reason why caffeine can disrupt sleep.
The precise neurological mechanism by which the homeostatic component works is a subject of intense scientific study and parts of the process remain a mystery.
Despite the unknowns however, this is a certainty: the longer an individual remains awake, the stronger the desire and need to sleep becomes.
We call this irresistible certainty the “Law of Prior Wakefulness”, and we will use this principle extensively in the STS.
There is no “normal” amount of sleep that’s right for everyone
Sleep, as a natural human phenomenon, is still not completely understood despite significant ongoing research. There is no one agreed-upon number experts use as the ideal amount of sleep for everyone to get.
However, determining the right amount of sleep for your own personal system is important because insufficient sleep has a number of negative consequences. A lack of sleep has been shown to negatively affect alertness, memory, problem solving, and overall health, as well as increase the risk of accidents. A 2003 study at the University of Pennsylvania School of Medicine demonstrated that cognitive performance declines with six or fewer hours of sleep. Other studies have shown that a lack of sleep increases cravings for fattening foods, and may contribute to obesity and diabetes.
The reverse is also true. Getting good sleep is considered an essential component of overall well being, enabling us to perform at our best during waking hours. Healthcare professionals recognize that quality sleep is a vital component of happiness, and is one of the best forms of preventive medicine.
So instead of a single number, sleep therapists generally recommend a range that is normal for most people. The National Sleep Foundation suggests that seven to nine hours of sleep for adults is optimal. A 2009 British study suggested consistently sleeping 6 to 8 hours per night may be best for health. Other studies have shown six to seven hours increase longevity.
A 2015 cross-cultural sleep study found those living today in some of the world’s few remaining preindustrial societies – meaning hunter-gatherer and subsistence farming groups without access to electric lighting or heated and cooled living spaces – generally spend about 7 to 8.5 hours in bed. These people average about 6 to 7 hours actually sleeping per night, with very little evidence of insomnia or other negative consequences of sleep deprivation.