In spite of how common sleep is, there are few bodily processes more mysterious to humans. For example, scientists are divided over the functionality of dreams: are they the brain's method to enhance long-term memory, or simply the product of random brain activity? What is the purpose of the considerable neural and physiological variations produced in the body during REM (or, rapid eye movement) sleep? What exactly is
the definition of sleep?
Though there are many unknowns, here are three fascinating insights into how our body keeps working even after we fall asleep.
While it is true that the number of active or "firing" neurons in the brain gradually decreases in the period from wakefulness to non-REM sleep, when we enter into REM sleep our brain can actually become just as active as if we were awake - if not more so!
During times we are awake, our brain sends out chemicals that help us stay awake. For example, the brain releases histamine as a neurotransmitter, and this chemical promotes wakefulness. (This is why so many "anti-histamine" medicines tend to make us sleepy.) On the other hand, as the day goes on our brain begins to increasingly signal us that it's time for bed. Apparently a chemical called adenosine accumulates in our brain throughout the day, and eventually begins to inhibit wake-promoting neurons. During periods of sleep, the brain continues to fire sleep-promoting neurons to maintain stable rest.
Fascinatingly, we are different from some mammals in that our whole
brain is involved in the sleep process at the same time. Other mammals, such as dolphins, actually only have one
hemisphere of their brain fall asleep in turn! (That gives a whole new meaning to the phrase "half-asleep!") This allows them to maintain a certain level of alertness all the time; and also permits them to periodically surface for air.
Due to a process called thermoregulation, our core body temperature actually drops 1 or 2 degrees Fahrenheit during non-REM sleep. Some scientists believe this method of conserving energy is one primary function of sleep. However, during the 10 to 30 minute increments of REM sleep, our body temperature drops even lower. During this time it is important that our body not lose too much heat; which is why it is so important to stay warm under those cozy blankets!
During sleep, our heart also gets a break from all the hard work it does circulating blood throughout our system during the day. Blood flow and blood pressure is noticeably decreased during non-REM sleep. Once again, however, during REM sleep our body's systems begin to work hard without us even knowing it. Variations in blood flow during REM sleep can sometimes cause arousal during sleep, although scientists don't know if this is a result of changes in the nervous system or a consequence of dream content.
Logically, in order to maximize the amount of sleep, and to enhance its quality, it is important that a mattress not inhibit blood flow throughout the cardiovascular system. Some mattresses have pressure points that constrict blood flow; and when the body signals that it's time to roll over and release that pressure, stable sleep is temporarily interrupted. So when selecting a mattress, aside from financial and environmental considerations, it is always good to factor in the physiological effects on your body. Our Natural Escape
mattresses, for example, feature contouring organic Dunlop latex that cradles the pressure points and helps with circulation as well as comfort.
For more information on the science of sleep, and how the body keeps working after we've already drifted off into unconsciousness, visit this intriguing series of articles from Harvard
. Perhaps with time, we will discover even deeper insights into how and why our body keeps active during our daily period of rest.