In her early 19th century verse, “An Address to the Night,” Scottish poet Joanna Baillie wrote, “From sleepless beds, unquiet spirits arise,” very dramatic and also very true.
The lines highlight the fact that a good night of sleep is essential to thinking clearly the next morning and being safe in the sky, and also down here on the ground. Modern safety literature has hundreds of references to fatigue causing human errors and accidents. One of the most well-known is the 1997 review in Nature by Drew Dawson and Kathryn Reid that studied critical task performance and found that 21 hours of wakefulness equated to the performance level of a subject with a blood alcohol level (BAC) of 0.9. That’s 10 times the legal driving limit, as we talked about in the post last month. The FAA has extensive literature on fatigue and lack of quality sleep that’s directly linked to aircrew errors and accidents. Fatigue has also been shown to lead to poor performance and errors in general work performance and in health care. Sleep is well documented as necessary for good health and specifically good cardiac function. As pilots, we know how strict the FAA regulations on aircrew rest are for all of these very good reasons. With this as background, it’s worth a little deeper dive into the topic to understand exactly what sleep is, and why it’s so critical to our safety and good health.
Sleep physiologists have a bunch of theories for our brain’s need to sleep, such as the “inactivity theory,” “energy conservation theory,” “restoration theory,” and the “brain plasticity theory.”
One thing for sure, sleep is an extremely complicated process that’s more than just closing your eyelids and counting sheep. It’s an active state of unconsciousness during which a bunch of very critical things are going on inside our heads. While we’re sleeping, the brain stays remarkably active and recent studies of brain function during sleep suggest that critical housekeeping chores go on such as removing toxins that build up during the day. During sleep, the brain is also making crucial chemical, physical, and structural changes that store memories and learned information from daytime activities as well as delete other memories and information that doesn’t get permanently stored. These structural changes are the way the brain stores information from training and studying by building new nerve connections. These little connections are called synapses and are microscopic contacts between nerve cells that use brain chemicals (neurotransmitters) to pass electrical impulses (i.e., information) between nerve cells. During the day, these connections are started up in response to the stimuli that the brain receives from the environment, study, and training, but it’s at night that recent data shows that these important connections are cemented into place. This is commonly called learning, or the reverse happens and the connections fall apart, commonly called forgetting. It also explains why staying up all night to “cram” for an exam the next day almost guarantees that you won’t remember much of anything for more than a few hours—hopefully long enough to pass the test. So if you spend a long day training or studying it’s crucial to get a good night’s sleep to process and store the information for later use. “Fitful” and non-restful sleep has been shown to be ineffective in storing the day’s learning and training.
Falling asleep is a complicated process that’s partially based on our internal “circadian rhythm” clock, which responds to the light-dark cycles. The circadian clock triggers a tiny little clump of cells in the center of the brain called the “pineal gland” to secrete a hormone, melatonin, that sets up the start of the sleep pattern. Melatonin is now commercially available and, although there are individual variations, some people find taking over-the-counter melatonin helps them to fall asleep as well as get on a new time zone after traveling. Waking up is the opposite of falling asleep and happens as the pineal’s secretion of melatonin falls after 6-8 hours.
This cyclic pattern of sleep is relatively predictable with two major phases, non-rapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep. Each phase has unique characteristics in the brain wave, muscle tones, and eye movement patterns. Just as the name implies, the hallmark of REM sleep is rapid eye movements, and it’s during this phase that the brain engages in most of those restorative chores and data storage functions of sleep. REM is also the phase of sleep responsible for dreaming, and except for the eye muscles, it’s characterized by total body voluntary muscle paralysis. That’s the way the body prevents neural stimuli from dreams from manifesting in actual motor activity during sleep. The brain stem plays a special role in REM sleep and sends signals to relax muscles essential for body posture and limb movements, so that we don’t act out our dreams and suffer injuries. Dreaming is an important function of sleep and everyone has dreams while sleeping. On average, you spend about 2 hours each night dreaming but may not remember most of your dreams. Its exact purpose isn’t known, but dreaming may help you process your emotions. Events from the day often invade your thoughts during sleep, and people suffering from stress or anxiety are more likely to have frightening dreams. Dreams can be experienced in all stages of sleep but are most vivid during REM sleep. Some people dream in color, while others only recall dreams in black and white.
There’s no magic “number of sleep hours” that works for everybody since some of the functions of melatonin secretion and sleep cycles are genetically predetermined. This explains why there is some variation in how much sleep individuals need. As all parents know, there are age-related variables in sleep requirements. Babies initially sleep as much as 16 to 18 hours per day, which is crucial to boosting growth and development of the brain. On average, school-age children and teens usually sleep about 9-10 hours per night. Most adults need 7-9 hours of sleep but after around 60, individual sleep needs tend to be shorter, lighter, and usually interrupted by multiple awakenings. As far as getting to sleep, be careful with “sleeping pills” if you have trouble falling asleep, since many can have a paradoxical effect and actually interfere with sleep and can cause agitation instead. A study published in 2015 showed that almost 80% of people who use sleep medication experience side effects like headaches, nightmares, dizziness, nausea, difficulty concentrating, impaired motor skills, lack of coordination, dry mouth, daytime drowsiness, depression, and periods of amnesia. Even over-the-counter sleep aids can have a negative impact on sleep quality that has important, and potentially negative, implications for pilots.
In the late 1600s Sir Francis Bacon, father of modern scientific theory, wrote, “Sleep is the silence that nourishes wisdom.” A more modern take on our nighttime needs came from a late-night TV comedian: “There are many theories on why humans need to sleep, but I’m pretty sure it’s to charge our phones.” Both might be true, but never forget that not only do our cell phones get charged during a good night of sleep, but, as Sir Francis knew centuries ago, our brains do too. Get a good night’s sleep to avoid “arising with unquiet spirits,” and next month we’ll talk about some abnormal and non-restful sleep patterns and some methods you can use to overcome them.