As the fall season begins to unveil its glorious colors, writing this article about sleep prompted a memory in me from my childhood of an autumn long ago.
Our family had gathered to celebrate Thanksgiving. The table was set. The candles were lit. Scrumptious aromas filled the dining room. The turkey and trimmings were presented, piping hot, to great admiration and applause. Mom, Dad, Granny, aunts, uncles, cousins, and children, all seated, were hungry and eager to begin the feast.
All except one, Granddad. He had gotten up from the table—just as the rolls had come out of the oven—in response to a call of Nature.
More minutes passed than we thought necessary for him to attend to the matter. At first, we looked sheepishly at each other. When our joyous conversations began to falter, and our looks of muffled embarrassment turned to worry, I got up from the table to ascertain what had happened to Grandpa. As I made my approach to the bathroom down the hall, I could hear the sound of water gently running. After knocking with no response, I discretely opened the bathroom door. To my surprise, relief, and puzzlement, there was Granddad, standing in front of the sink with his hands in the wash basin and the water running, softly snoring and fast asleep!
Sleep is a naturally recurring state of mind and body. Sleep is how we spend a third of our lives. Important biology is going on inside our brains and inside our bodies when we are asleep. Some parts of our brains actually are more active during the sleep state than during the wake state! And yet, as demonstrated by Granddad, what a complex and mysterious state of being sleep is.
What causes us to fall asleep? What prompts us to wake up again? Why do we need to sleep in the first place? Advances in neurobiology and medical science are beginning to reveal its secrets. One-word answers to the three questions I posed are: melatonin, cortisol, and health.
Beginning with our health, here are just a few of the ways that a good night’s sleep helps maintain our vim and vitality.
Stores of energy in the brain are resupplied when we are asleep; facts and memories of the day are consolidated and stored for future retrieval.
Sleeping well enhances our ability to creatively interpret these facts and memories to solve complex problems when we awake.
The brain releases growth hormone into the bloodstream, primarily during the first four hours of sleep. Growth hormone plays a vital role in tissue repair.
Beta-amyloid—a biochemical associated with the development of dementia if it builds up too much in our brain tissues – is flushed out of our brains during the sleep cycle.
Establishing and maintaining regular sleep patterns often helps ameliorate adverse symptoms experienced by people suffering from schizophrenia, bipolar disorder, and depression.
In myriad ways, our long-term cognitive, emotional, and mental health, indeed, our overall health all are enhanced by adequate and restful sleep.
To receive the benefits of sleep, we must of course, fall asleep. Science has come to understand the important role our eyes play helping us do just that.
It has been long recognized that rods and cones in the retina of our eyes convert light into neurological signals that the brain can interpret, providing us the ability to see. Rods, which are much more numerous than cones, allow us to see in dim light. Cones provide us with color vision in bright light. What science has now revealed is that, independent of the rods and cones, our eyes have other photoreceptors that perceive the circadian rhythm of daylight and nighttime. By conveying this circadian information to our brains, we synchronize our internal biological clocks with the cyclical light and darkness patterns of the external world.
Specifically, non-vision photoreceptors in our eyes are neurologically hardwired to the internal biological clock in our brains—the suprachiasmatic nucleus in the hypothalamus gland located behind our eyes. This neurological hardwiring continues on from the hypothalamus—via the spinal cord—to the pineal gland located near the center of our brains. Prompted by the circadian signal originating in the non-vision photoreceptors in our eyes, the pineal gland synthesizes melatonin, the “darkness hormone.”
Under natural circumstances in healthy individuals, concentrations of melatonin in the bloodstream peak in the dead of night (around 3 to 4 a.m. in the morning), reaching levels about 5 times higher than they are in the middle of the day. High melatonin levels signal to our bodies it is time to go to sleep and to stay asleep. Blue light suppresses melatonin production. Avoiding blue light (or wearing goggles that block blue light) for a few hours before bedtime promotes sleepiness.
Over the course of a month, the internal biological clocks of people who—either from birth or injury—do not have eyes slowly drift in and out of sync with day and night. For most days, production of melatonin by the pineal gland is not aligned properly with the onset of darkness. The result is many sleepless nights and long naps during the day. Treatment with melatonin tablets can reduce the time of sleep onset, increase sleep duration, and keep their sleep cycle in sync with nighttime.
Obviously, we must not only be able to fall asleep and stay asleep, we must be able to wake up again. To counterbalance the sleep signal of melatonin, our bodies generate the steroid hormone cortisol, the “stress hormone.” The same biological clock that regulates the production of melatonin also regulates the production of cortisol. In this case, however, the command to make cortisol originates in the pituitary gland of the brain. Based upon signals received from our internal biological clock located in the hypothalamus, the adjacent pituitary gland sends a signal (via a peptide called ACTH) through the vascular system to the adrenal glands, which are located just above the kidneys. When the adrenal glands receive the ACTH signal, they produce cortisol.
Cortisol gets our bodies ready to wake up and do the work of the day. Average levels of cortisol in the blood are highest at dawn and they stay high during the morning. They gradually fall throughout the afternoon reaching baseline levels as night begins.
Fascinatingly, while average levels of cortisol rise and fall in a smooth pattern over the course of a day, the actual levels of cortisol in the bloodstream oscillate sharply each hour! At night, the hourly oscillations are small, like a small child jumping up and down on a trampoline. During the day, fluctuations in the levels of cortisol in the blood become much larger, like a skilled gymnast bouncing up and down on a trampoline performing a routine.
More interestingly still, patients report feeling lethargic when they are continuously administered cortisol to keep blood levels consistently high. It is the augmented hourly swings of cortisol that give us the “get up and go” feeling.
Sleep is an essential aspect of what makes us human. Sleep is a wonderful gift, improving our health and our outlook on life. It offers a daily sabbath. It provides a land of imagination and dreams. (Until robots need sleep, their artificial intelligence will never fully emulate ours.) Honor it and shield it from the ravages and insults so prevalent in the modern age, and it will bless you.