Most animals on Planet Earth spend their lives alternating between two states of being, which we call “sleep” and “awake.” This alternation is rooted in an essential condition of our planet – that it rotates on its axis once a day, a day being defined by the time that it takes for this planet of ours to accomplish that rotation. Therefore, all of us – humans and animals alike – are evolved to adapt to an environment in which light is invariably followed by darkness, which is again invariably followed by light. We all, in a variety of different ways, adapt to this alternation making profound changes in our physiologic functions, from waking to sleep and then back to waking. These changes are generally referred to as our circadian rhythm.

There may be planetary bodies out there somewhere in our galaxy (or perhaps the next galaxy over) that are equally exposed to the light of two stars so that there is no alternation between light and darkness. Is it possible that the inhabitants of such a planet do not alternate between sleep and waking, and that the restorative effects that we earthlings derive from sleep are acquired by those beings through some other process? In my perhaps over-optimistic view, there aren’t any limits to what’s possible, but for the moment let’s stick to what sleep means here on our home planet, and particularly what it means to the fellow-members of our species.

We humans spend about one-third of our lives asleep. Getting good sound sleep, and getting enough of it, is as essential to our lives as nourishment, and it would not be wrong to refer to sleep as a form of nourishment for our bodies and, in particular, for our brains. Sleep is vital to a large number of brain functions, especially how our individual brain cells communicate with each other. The pathways between our neurons are how we learn, form memories, concentrate, and respond to the information that our five senses import from the world outside our brains. Without good sleep we have difficulties learning and concentrating. In fact, our brains stay remarkably active during sleep. Sleep plays a sort of housekeeping role in our brains, removing toxic substances that tend to accumulate during our waking hours.

Everyone needs sleep, but its biological purpose remains a mystery. Sleep affects almost every type of tissue and system in the body – from the brain, heart, and lungs to metabolism, immune function, mood, and disease resistance. Research shows that a chronic lack of sleep, or getting poor quality sleep, increases the risk of disorders including high blood pressure, cardiovascular disease, diabetes, depression, and obesity. Sleep is a complex and dynamic process that affects how we function in ways scientists are now beginning to understand.

The philosopher/psychologist William James in his 1890 classic, The Principles of Psychology, speculated on the nature of sleep – or, rather, on the underlying differences between consciousness and the unconscious.

“The life of the individual consciousness in time seems, however, to be an interrupted one, so that the question, ‘Are we ever wholly unconscious?’ becomes one which must be discussed. Sleep, fainting, coma, epilepsy, and other ‘unconscious’ conditions are apt to break in upon and occupy large durations of what we nevertheless consider the mental history of a single man. And, the fact of interruption being admitted is it not possible that it may exist where we do not suspect it, and even perhaps in an incessant and fine-grained form?

This might happen, and yet the subject himself never knows it. We often take ether and have operations performed without a suspicion that our consciousness has suffered a breach. The two ends join each other smoothly over the gap; and only the sight of our wound assures us that we must have been living through a time which for our immediate consciousness was non-existent. Even in sleep this sometimes happens: We think we have had no nap, and it takes the clock to assure us that we are wrong. We thus may live through a real outward time, a time known by the psychologist who studies us, and yet not feel the time, or infer it from any inward sign. The question is, how often does this happen? Is consciousness really discontinuous, incessantly interrupted and recommencing (from the psychologist’s point of view)? and does it only seem continuous to itself by an illusion analogous to that of the zoetrope? Or is it at most times as continuous outwardly as it inwardly seems?”

(Zoetropes, by the way, were devices that simulated present day motion-picture animation. They were round plates with a cylindrical wall into which slits were cut. On the inside of the wall were pictures of something – a running horse, for instance – at successive points of motion, like individual frames of an action film. When the zoetrope was spun, the images through the slits had the appearance of continuous motion.)

If you ask why I am quoting from a book that’s more than a century old in a discussion of sleep, it’s because in contemporary writing about sleep I haven’t run across any hint that there are puzzles and uncertainties about essential differences between sleeping and waking. Those puzzles and uncertainties persist.

(And if you think William James’s writing is difficult, you should have a try at the writings of his brother Henry.)

Biological mechanisms that regulate sleep

The daily alternations between light and darkness and the profound effect these have on our physiologic response are called “circadian rhythms.” Circadian, of course, refers to the rotation of our planet every 24 hours. Circadian rhythms exercise control over a wide range of body functions, including not only the shift from sleepiness to wakefulness, but also body temperature, metabolism, and the release of hormones. They synchronize with environmental cues such as light and temperature, which are principally determined by the actual time of day. However, they tend to continue even in the absence of these cues.

Melatonin, a hormone released by the pineal gland as darkness takes over, produces feelings of sleepiness. Sleep-wake homeostasis keeps track of the need for sleep.  The homeostatic sleep drive reminds the body to sleep after a certain time and regulates sleep intensity.  This sleep drive gets stronger the longer we are awake and causes us to sleep longer and more deeply after a period of sleep deprivation.

Factors that influence our sleep-wake cycle include medical conditions, medications, stress, sleep environment, and what we eat and drink.   The strongest of these is the exposure to light.   Specialized cells in the retinas process light and tell the brain whether it should advance or delay our sleep-wake cycle.   Exposure to light can make it difficult to fall asleep and return to sleep when awakened.

Night shift workers often have trouble falling asleep, and also have trouble staying awake at work because their natural circadian rhythm and sleep-wake cycle is disrupted.  In the case of jet lag, circadian rhythms fall out of sync with the actual times of day in different time zones, creating a mismatch between the internal clock and the actual clock.

How much sleep do we really need?

As we all doubtless know, new babies need a lot of sleep – initially 16 to 18 hours a day, which they need for growth and development, especially of the brain. Toddlers get by with a little less, perhaps 12 hours plus maybe a nap. By the time kids get to school age, their sleep needs drop to about 9.5 hours per night. Adults make do with 7 to 9 hours of sleep, and as they get older, they (we!) tend to sleep for shorter periods.

In general, many people are getting less sleep than they need, due to longer work hours and the availability of round-the-clock entertainment and other activities. If this “entertainment” consists of doing something on the computer or watching TV, they are likely affected by the “blue screen” phenomenon, which adversely affects sleep. Many people feel they can catch up on missed sleep during the weekend but, depending on how sleep-deprived they are, sleeping longer on the weekends may not be adequate.

Sleep phases

We alternate between two basic sleep phases. One has been designated “rapid eye movement sleep,” commonly abbreviated to REM sleep, and the other simply as non-REM sleep. Each phase is linked to specific brain waves and neuronal activity. We cycle through all stages of non-REM and REM sleep several times during a typical night. As wake-up time draws near, increasingly longer, deeper REM periods are predominant.

When we first drop off to sleep, the dominant phase is non-REM sleep. The first sleep phase is designated as stage 1 non-REM sleep, which is the changeover from wakefulness to sleep.   During this short period, usually lasting just a few minutes of relatively light sleep, our heartbeat, breathing, and eye movements slow, and our muscles relax, with occasional twitches.  Our brain waves begin to slow from their daytime wakefulness patterns.
The phase designated as stage 2 non-REM sleep is a period of light sleep before we enter deeper sleep. Heartbeat and breathing slow, and muscles relax even further. Body temperature drops and eye movements stop completely.  Brain wave activity slows, but is marked by brief bursts of electrical activity.  We spend more of our repeated sleep cycles in stage 2 sleep than in other sleep stages.

Stage 3 non-REM sleep is the period of deep sleep that we need to feel refreshed in the morning.   We experience longer periods of stage 3 non-REM sleep during the first part of our sleep.  Heartbeat and breathing slow to their lowest levels during this part of the sleep.  Our muscles are entirely relaxed and if someone tries to waken us for any reason, they will find it very difficult.  Our brain waves become even slower.
In contrast, REM sleep first occurs about 90 minutes after we fall asleep.  Our eyes move rapidly from side to side behind our closed eyelids.  Brain wave activity is similar to what it is during wakefulness. Breathing becomes faster and irregular, and our heart rate and blood pressure increase to near waking levels.  By far the majority of our dreams happen during REM sleep, although some can also occur in non-REM sleep.   Our arm and leg muscles become temporarily paralyzed, which prevent us from acting out our dreams, which might be highly inconvenient.   However, as you no doubt know, some people get out of bed and wander around while essentially still asleep. As we age, less of your less of our sleep time is REM sleep.

Brain structures that are involved in our sleep-wake cycles

This part of the piece is a bit more complex, but may be of interest. Several different parts of our brains are active in controlling the phases of our consciousness, as we alternate between sleeping and waking.

Hypothalamus

The hypothalamus is a small structure deep inside the brain, under the thalamus and over the pituitary gland. It contains groups of nerve cells that act as control centers affecting sleep and arousal.

Suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN) consists of thousands of cells that receive information about light exposure directly from the eyes. In response to this exposure, the suprachiasmatic nucleus exercises control over our behavioral rhythm.  Some people with damage to this group of cells tend to fall asleep erratically throughout the day because they are not able to match their circadian rhythms with the light-dark cycle.   Most blind people maintain some ability to sense light and are able to modify their sleep/wake cycle.

Brain stem

The brain stem, at the base of the brain, communicates with the hypothalamus to control the transitions between wake and sleep.   (The brain stem includes structures called the pons, medulla, and midbrain.)   Sleep-promoting cells within the hypothalamus and the brain stem produce gamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter, which acts to reduce the activity of arousal centers in the hypothalamus and the brain stem.  The brain stem (especially the pons and medulla) also plays a special role in rapid eye movement (REM) sleep. It sends signals to relax muscles essential for body posture and limb movements, so that we don’t act out our dreams.

Thalamus

The thalamus acts as a relay for information from the senses to the cerebral cortex (the covering of the brain that interprets and processes information from short- to long-term memory).  During non-REM sleep, the thalamus becomes inactive, letting us tune out the external world.  But during REM sleep, the thalamus is active, sending the cortex images, sounds, and other sensations that constitute our dreams.

Pineal gland

The pineal gland is located in the mid-line of the brain and is outside of the blood-brain barrier. It is shaped like a tiny pinecone, which is how it got its name. Its main job is to help control the circadian cycle. It receives signals from the SCN and increases production of melatonin, the hormone which helps put us to sleep. People who have lost their sight and cannot coordinate their natural wake-sleep cycle using natural light can stabilize their sleep patterns by taking small amounts of melatonin at the same time each day.  Scientists believe that peaks and valleys of melatonin over time are important for matching the body’s circadian rhythm to the external cycle of light and darkness.

Basal forebrain

The basal forebrain, near the front and bottom of the brain, also promotes sleep and wakefulness, while part of the midbrain acts as sort of an alarm clock.  Release of adenosine (a chemical by-product of energy consumption by our cells) from the basal forebrain and probably other regions contributes to the feeling of sleepiness.  Caffeine counteracts sleepiness by blocking the actions of adenosine.

Amygdala

The amygdala, an almond-shaped structure involved in processing emotions, becomes increasingly active during REM sleep.

Did you really need all that information about the different brain structures? Probably not, but I stuck it in to show you how complex the sleep-wake cycle is.

Dreaming: what is that all about?

We all have dreams, and we spend probably a couple of hours every night dreaming. Mostly, dreams happen during the rapid eye movement phase of sleep, and since it has been observed that non-human animals also experience REM sleep, we can assume that animals also have dreams. As a former dog owner, I can testify that dogs have fairly vivid dreams.

There have been many, many theories as to why we have dreams and what these dreams mean. Throughout much of our history, dreams have been associated with the supernatural in some form. In ancient times, dreams were often interpreted as communications from deities, who were commanding the dreaming being to carry out certain specific actions. Since it was frequently difficult to figure out from the dream just what the deity was ordering the dreamer to do, this led to the necessity for intermediaries to interpret the dream for the dreamer, telling the dreamer what it was that the deity was ordering him/her to do.

Even when this particular view of dreaming faded from prominence, the general sense that dreaming connected us with another reality persisted. That is to say, the content of our dreams did not entirely come from our own brains and minds. This view to some degree continued until well into the 19th century, when a number of other views and interpretations came into prominence.

As far as I know, Charles Darwin did not himself discuss dreams or their role, but from the perspective of natural selection, dreams must provide some kind of benefit, or else they would not be a part of our lives. A physician in Hamburg, Dr W. Robert, suggested that dreams serve a specific and necessary function, which is either to complete or erase fleeting sensory impressions that were not fully processed during our waking hours. In dreams, according to his view, incomplete material is either removed or incorporated in our memories. Sigmund Freud proposed that dreams preserve sleep. He proposed a dream category, the wish-fulfillment dream, in which the dreamer derives a degree of satisfaction from dreaming about a desired experience. Freud wrote that dreams “serve the purpose of prolonging sleep instead of waking up.  Dreams are the GUARDIANS of sleep and not its disturbers.”

A number of theories have been proposed regarding the essential function of dreaming. Here are brief summaries of a few of them:

• Dreams promote some aspect of the learning process. A 2010 Harvard study came up with evidence that frequent dreaming was correlated with improvements in the learning process.
• Dreams are like the cleaning-up operations of computers when they are offline, removing parasitic nodes and other “junk” from the mind during sleep.
• Dreams serve a quasi-therapeutic function, enabling the dreamer to process trauma in a safe place.
• Dreams aid survival by replicating physical and interpersonal threats and providing the dreamer with practice in dealing with them.
• Dreams furnish a simulation for training social skills and bonds.
• Dreams enable the dreamer to learn from novel situations.

Any of these theories have some merit and relevance, but even taken together – in my opinion – they do not provide a complete explanation of the role of dreams in our lives.

When I think about my dreams, I am somewhat dubious whether they fit into those particular categories. One kind of dream I have fairly frequently might be thought of as a sort of wish-fulfillment dream. For example, in the dream I am in New York City, where I lived a good chunk of my life. I find myself in an unfamiliar street in front of a building that resembles a Gothic cathedral, with an elaborate front decorated with columns, arches, sculptures of all kinds, leaded windows, and all manner of beautiful details. The building is not a church. It is flush with the street, not set off in a churchyard. I see that other buildings on that street are also elaborately decorated. Buildings of that sort are what I want to see in the city. The dream fulfills my wish for a cityscape that I would love, and also helps process the trauma of seeing the brutal concrete and glass buildings that have invaded the city.

I also see some people in my dreams very clearly and distinctly, but I have no idea who they are. These are probably real people whom I have briefly seen in my waking life, without fixing my attention on them. Their images float in my mind, and the dreams in a certain sense complete the experience.

Like most of us, I quickly forget the vast majority of my dreams. They happen, fulfilling whichever of those functions they serve, and then they quickly evaporate when I wake up. At least, that’s what happens most of the time. I am left with a sense that dreaming is definitely an important and vital part of my brain’s activity while I am sleeping.

How serious a threat is sleep apnea?

According to the American Medical Association, as many as 30 million people in the US probably have sleep apnea to some degree, although only 6 million have been diagnosed with this condition. I don’t know how they arrived at these figures; the assumption that for every person in the US who has been diagnosed with sleep apnea there are four more undiagnosed seems to be a bit “out of the blue,” but the AMA is usually a responsible organization and is not prone to wild guessing.

Sleep apnea, as you know, is a condition in which we stop breathing for a short period while we are asleep. The root of the word “apnea” is the Greek “pneo” meaning “to breathe,” from which come “pneumonia” and “pneumatic.” In French, automobile tires are called “pneus,” because they are inflated with air, like our lungs.

There are two general types of sleep apnea. The more common type is obstructive sleep apnea, which happens when the muscles in the back of the throat relax. These muscles support a triangular piece of tissue hanging from the soft palate called the uvula, and also the tonsils, the side walls of the throat, and the tongue.

When these muscles relax, the airway narrows or closes as we breathe in. We cannot get enough air, which tends to lower the oxygen level in the blood. The brain senses that we cannot breathe and briefly wakes us so that we can reopen the airway. This awakening is usually so brief that we do not remember it.
We might snort, choke or gasp. This pattern can repeat itself 5 to 30 times or more each hour, all night. This makes it hard to reach the deep, restful phases of sleep.

Central sleep apnea is a less common form, which occurs when the brain fails to send signals to the muscles that bring air in and out of our lungs. This means that for a short period we make no effort at all to breathe. We might wake up with a feeling of shortness of breath and have a difficult time getting back to sleep and staying asleep.

A number of factors increase the risk of both forms of sleep apnea.

Obstructive sleep apnea risk factors

1. Excess weight.  Obesity greatly increases the risk of obstructive sleep apnea. Fat deposits around the upper airway can obstruct breathing.
2. Neck circumference.  People with thicker necks tend to have narrower airways.
3. A narrowed airway.  Tonsils or adenoids also can enlarge and block the airway, particularly in children. Some people are born with narrow airways.
4. Male gender.  Men are two to three times more likely to have sleep apnea than women. However, women increase their risk if they are overweight or if they have gone through menopause.
5. Age.  Sleep apnea occurs significantly more often in older adults.
6. Family history.  Having family members with sleep apnea tends to increase the risk.
7. Use of alcohol, sedatives or tranquilizers.  These substances relax the muscles in your throat, which can worsen obstructive sleep apnea.
8. Smoking.  Smokers are three times more likely to have obstructive sleep apnea than people who have never smoked. Smoking can also increase inflammation and fluid retention in the upper airway.
9. Nasal congestion.  Persons who have trouble breathing through the nose, whether from an anatomical problem or allergies, are more likely to develop obstructive sleep apnea.
10. Medical conditions.  Congestive heart failure, high blood pressure, type 2 diabetes, polycystic ovary syndrome, hormonal disorders, prior stroke and chronic lung diseases such as asthma are some of the conditions that may increase the risk of obstructive sleep apnea.

Central sleep apnea risk factors

• Being older.  Middle-aged and older people have a higher risk of central sleep apnea.
• Being male.   Central sleep apnea is more common in men than in women.
• Heart disorders. Having congestive heart failure increases the risk.
• Using narcotic pain medicines.  Opioid medicines, especially long-acting ones such as methadone, increase the risk of central sleep apnea.
• Stroke.  Having had a stroke increases the risk of central sleep apnea.

Sleep apnea complications

• Both obstructive and central sleep apnea can bring serious complications to the patient. These risk factors include conditions of concern:
• Daytime fatigue.  The repeated awakenings associated with sleep apnea make typical restorative sleep impossible, sometimes leading to severe daytime drowsiness, fatigue and irritability.
• Persons with sleep apnea may have trouble concentrating and may sometimes fall asleep at work, while watching TV or even when driving. People with sleep apnea have an increased risk of motor vehicle and workplace accidents.
• Children and adolescents with sleep apnea might perform poorly in school or have behavior problems.
• High blood pressure or heart problems.  Sudden drops in blood oxygen levels that occur during obstructive sleep apnea can increase blood pressure and strain the cardiovascular system. Multiple episodes of low blood oxygen (hypoxia or hypoxemia) can lead to sudden death from an irregular heartbeat.
• Obstructive sleep apnea may also increase the risk of recurrent heart attack, stroke and irregular heartbeats, such as atrial fibrillation.
• Type 2 diabetes.  Having sleep apnea increases the risk of developing insulin resistance and type 2 diabetes.
• Complications with medicines and surgery.  Obstructive sleep apnea is also a concern with certain medicines and general anesthesia. People with sleep apnea might be more likely to have complications after major surgery because they’re prone to breathing problems, especially when sedated and lying on their backs.
• Liver problems.  People with sleep apnea are more likely to have irregular results on liver function tests, and their livers are more likely to show signs of scarring, known as nonalcoholic fatty liver disease.

I have no data on the frequency or likelihood of a person with either form of sleep apnea developing any of the above symptoms. My estimate is that the more serious and concerning symptoms are much less frequent than the milder symptoms. That is to say, daytime fatigue is much, much more common than the risk of liver problems. And, to my knowledge, there is no evidence of a causal mechanism that would link sleep apnea with type 2 diabetes or liver problems. But even without evidence of a specific mechanism, it seems obvious that any condition that impairs our sleep – sleep being a necessary part of our existence – would have harmful effects on our overall health. Which leads us to the necessity of treating sleep apnea when it is present.

Treatment for sleep apnea

There is no drug treatment available for sleep apnea. At this point, the only available means of treating sleep apnea, whether obstructive or central, is a device called a continuous positive airway pressure (CPAP) machine. A CPAP machine delivers just enough air pressure to a mask to keep the upper airway passages open, preventing snoring and sleep apnea. The idea of needing to sleep wearing a mask-like device that is connected to a machine is obviously unwelcome. However, from what I have been able to learn, CPAP machines are much, much more comfortable than when they were first introduced. A person whom I have known for many years asserts that they are “no big deal.” And, of course, far preferable than risking some of the more serious complications of sleep apnea.

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It’s probably pretentious of Doc Gumshoe to try to sum up in a single piece a condition which occupies about a third of our lives, and if I have failed to address any factors of concern, do please let me know and I will do some additional sleuthing and get back to you – I hope – with some answers.

And in the meantime, more news about medical and health topics of interest keeps popping up. More about COVID, of course, plus recent Alzheimer’s findings, and news about antibiotic resistance (which is of major concern), chronic fatigue syndrome, and the diagnosis of pancreatic cancer.

Stay well and many thanks for any and all comments. Best, Michael Jorrin (aka Doc Gumshoe)

[ed note: Michael Jorrin, who I dubbed “Doc Gumshoe” many years ago, is a longtime medical writer (not a doctor) and shares his commentary with Gumshoe readers once or twice a month. He does not generally write about the investment prospects of topics he covers, but has agreed to our trading restrictions.  Past Doc Gumshoe columns are available here.]