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Pruning the overgrown garden of our mind is one of five leading theories.
According to a National Sleep Foundation study, 45 percent of Americans have reported that, despite getting an adequate amount of sleep (about seven and a half hours a night), they feel that the quality of their sleep is poor or only fair. And 20 percent of Americans do not wake up feeling refreshed. Sixty-seven percent of American who have reported poor or only fair quality sleep also report that their health is poor or only fair.
Stress and/or poor quality of life seems to contribute to the sleep/health connection. People making less than $20,000 annually, those who have no college education, or those in the prime working ages of 30-64 years old (presumably more stressful years) were the primary groups reporting poor sleep quality and sub-optimal health.
Sleep issues were also divided among genders. Women more often reported suffering from insomnia, while men more often suffered from snoring and sleep apnea problems. “It is well-established that men are at much greater risk of obstructive sleep apnea than women and this could explain the differences in snoring, which can be a sign of sleep apnea. The increased rates of insomnia in women is not fully understood but may be related to increased anxiety or depression or simply gender differences in willingness to report a problem,” Kristen Knutson of the National Sleep Foundation commented of the poll findings.
The mattress company Amerisleep recently conducted an interesting (though less than purely scientific) sleep survey, using as a guide the Instagram hash tags #Tired and #Goodnight. The survey shed some interesting light on America’s sleep habits. For instance, the most tired state (based on most often posting #Tired) turns out to be Hawaii (too much surfing, we’re guessing). The least tired state? Iowa (you’d think the Iowa primary would have worn them out). Turns out the city that never sleeps, based on the times #Goodnight was posted, isn’t New York City after all; it’s La Jolla, California, which turned in at 12:34am on average. The Big Apple, in fact, was actually one of the early-to-bed cities, averaging a 9:09pm #Goodnight time. Based on how often we post #Tired, we are apparently most tired during the months of May, June and April.
Back when our ancient ancestors came home to their caves after a hard day of mastodon hunting, they did what many of us do today after a tough day at the office. They dropped their briefcases…uh, spears…and sacked out for the night, their tired bodies demanding a good night’s sleep. But why do we need to sleep? The probable answer is that evolution deemed that the things that happen in our bodies while we sleep are more important for our survival than the things (like hungry saber-toothed tigers) that go bump in the night.
Much like when we go without food, our body produces the sensation of hunger, when we go without sleep, it produces the sensation of sleepiness. “As far as I know, the only reason we need to sleep…is because we get sleepy,” sleep researcher William Dement, co-discoverer of REM sleep and oft-considered the father of sleep medicine, told National Geographic. Researchers have come to believe that this feeling of sleepiness may be due to the waking hours buildup of a cell waste-product called adenosine. One effect of too much adenosine is to the perception of feeling tired. Once asleep, our bodies have a chance to clear out the adenosine, and we usually awake feeling refreshed. (Caffeine, by the way, counteracts the effects of adenosine, which is why it helps make us feel more alert.)
Discovering the reasons why we sleep is an Easter egg hunt we have just begun, but we are beginning to find some clues and present some theories that may eventually shed light on the activity we spend a third of our lives doing.
1. Pruning the overgrown garden.
When the brain takes in new information, it literally builds new pathways between brain cells. These new connections, known as synaptic connections, allow neurotransmitters, chemical messengers like serotonin and dopamine, to travel through the brain. But not all pathways are created equal. Some are inefficient. Some are broken. When there are too many inefficient pathways in your brain, you will likely feel foggy-headed, indecisive or just plain inefficient. This is where sleep comes in. Scientists now believe that when we sleep, we effectively prune the weeds from our brains. Cells called glial cells do this synaptic pruning. Some glial cells work to speed up the connection between neurons, while others are the brain’s gardeners, called microglial cells, and they literally dispose of the synaptic connections that are inefficient or unused and are clogging the pathways. When we sleep, our brain cells actually shrink so as to make room for the microglial cells to move in and sweep away the detritus. If you have ever wondered why sleeping on a problem often results in waking up with a clearer idea of the solution, you can thank your brain gardeners for that.
2. Restorative construction.
It has long been suspected that sleep is a way for the body to restore and repair itself during a period of inactivity. Many studies in recent years seem to have borne this theory out. One in particular was an (appalling cruel) animal study in which the subjects were deprived completely of sleep. The animals suffered a complete breakdown of the immune system and died within weeks. A study out of Surrey University showed how certain genes that are linked to inflammation, a possible cause of heart disease and stroke, were more active during times of sleep deprivation. Other studies have shown that major restorative activities like the release of growth hormones, tissue repair, and protein manufacture occur primarily during sleep.
3. Conservation of energy.
In times past, the search for food was the human race’s primary activity. Hunting down that mastodon was not a task to be taken lightly! Food was not the plentiful commodity it is today (or at least that it is in the West). Obtaining food was essential to supply the body with energy to sustain itself. But hunting it down also burned up a lot of energy. Many researchers believe that the activity of sleep evolved as a way for the body to remain inactive, save energy during the least efficient times to procure food (night), and reload the battery so to speak. And in fact, the body in sleep burns as much as 10% less energy, with body temperature dropping and calorie demand falling.
4. Protection of the species.
One of the earliest theories of why we sleep posited that evolution came up with sleep as a way to protect our existence. The theory went, active humans were noisy humans. Activity attracted potentially dangerous nocturnal animals that might eat us. Sleep made us relatively still and quiet, thus minimizing our chances of becoming prey. (Some scientists shoot down this theory by pointing out that going to sleep, closing our eyes, and becoming immobile for long periods of time would make us sitting ducks for saber-toothed tigers or whatever else lurked in the dark.)
5. Organizing the closet.
Newborn babies sleep as much as 14 hours a day. Sleep theorists use this as a jumping-off point to ask whether sleep is a way to develop and organize the growing brain. This is known as brain plasticity, and for adults, would be related to the gardening theory (#1 above) in adults.
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