Sleep

Sleep

Dr. C. George Boeree

Simple animals become inactive whenever possible -- they rest. The purpose of rest is to conserve energy, and, while at it, restore the organism. By restore, I mean get things back to a baseline condition needed for later activity -- especially clearing out waste products that build up during activity.

In higher animals, the nervous system becomes increasingly important to the functioning of the animal. Being a particularly high-maintenance system, the nervous system requires considerable rest and restoration. Many animals have found temporal niches -- i.e. some kind of daily cycle of activity and rest -- and evolution has taken advantage of the rest period and uses the time to restore the nervous system. This, of course, is sleep.

So sleep is probably devoted to the removal of waste products from the nervous system (and elsewhere, of course), especially the build up of neurotransmitters and hormones between cells. Cells that have been particularly active will, naturally, have greater build ups of chemicals. In the process of cleanup, neurons often fire “accidentally” throughout the night, triggering sequences of firings. Sometimes, for example, a person in deep sleep will get up and perform some routine function such as getting dressed or making coffee -- sleepwalking.

Sleep goes in cycles -- first moving quickly into deep, restorative sleep, then coming back up towards wakefulness, then back down again, and so on. Presumably, this cyclical pattern exists because sleep is somewhat dangerous for animals, and it is important to check on your situation from time to time. In social animals, it is likely that one or another individual will be near wakefulness at all times, and so be available to sound an alarm if needed.

When it is light, information from the eyes go to a small area of the brain (the suprachiasmatic nucleus, if you must know) and keeps it from releasing a hormone called melatonin. When it is dark, the melatonin is released and tells us to sleep. For this reason, some people like to call it "the Dracula hormone," since it only comes out at night!

Stages of sleep

Different parts of your night's sleep have different characteristics, which have lead researchers to suggest four stages. The most important source of information about the stages is the EEG (electroencephalogram). Several electrodes (small metal discs) are pasted to your scalp and the tiny electrical rhythms of resting neurons are recorded, traditionally on moving sheets of paper. Nowadays, of course, we use computers.

When you are awake and busy (at least mentally), these "brain waves" are desynchronized, which means that they don't show a clear rhythm. They are recorded as small, rapid, and very irregular marks on the EEG paper.

Underlying the jagged marks, though, is a base rhythm called beta waves, which are from 13 to 17 cycles per second (cps). Sometimes, when we are very alert yet momentarily not thinking about anything in particular, these waves become synchronized, and you can see the beta wave pattern on the EEG.

When you begin to relax and empty your mind, you begin to generate alpha waves, which are from 8 to 12 cps. This is usually a very pleasant state to be in, so much so that some people have even promoted the "alpha state" as something akin to meditation.

When you enter into stage one sleep, the waves begin to slow down, and become theta waves (4 to 7 cps). In addition, we enter into a state of flaccid paralysis of the large muscles, which means that your muscles become very relaxed and no longer respond to motor messages from the brain. Sometimes, as we move into this paralysis, our body responds as if we were falling, and we have a sudden jerk called myoclonus.

After a while, we go into stage two. The EEG shows more and more slow theta waves. In addition, we occasionally see a strange wave pattern called a sleep spindle, which consists of very rapid, 15 cps, bursts of activity.

After this, we enter into stage three. Now we see the very slow delta waves, which are 3 cps and slower.

And finally, we enter stage four, the deepest sleep. Now the EEG shows more than 50% delta waves. Stage four is where we are most likely to find night terrors and sleep walking. Night terrors are periods of extreme emotional arousal rarely accompanied by imagery (as in dreams and nightmares). Sleep walking is where a person gets out of bed and wanders about, sometimes doing routine activities such as getting dressed. This is common among children, and parents occasionally find their kids standing at the bus stop in their pajamas. Obviously, there is no paralysis in stage four! Usually, you don't need it.

After stage four, you begin to go back up the stages, until you reach stage one again. This is sometimes called stage one emergent, and it has one particularly impressive quality: Dreams. Dreams are accompanied by movement of the eyes, which can also be recorded with the EEG machine. Because of this, stage one emergent is also called REM sleep (for "rapid eye movement"). Here you can see the purpose of the flaccid paralysis mentioned earlier: If we weren't paralyzed we would likely act out our dreams!

Unfortunately for some people, the small muscles are not paralyzed -- so it is stage one emergent where we see sleep talking. Sometimes, you can actually engage someone in a small conversation in this stage! It is also interesting that the fingers are not paralyzed, and so we can also see deaf people signing in their sleep.

In an average night, you may go through about four or five cycles of stages, each cycle taking about 90 minutes. You usually go less deep each cycle, so that most of your deep, stage four, sleep occurs in the first half of the night. REM or dream sleep is about 20% of your total sleep, in four or five sessions. Unless you actually wake up, though, you rarely remember the first three or four dream sessions.

Pathologies of Sleep

The most common sleep pathology is simple lack of sleep! Most people need from 7 to 9 hours a night, and yet relatively few people actually get that. Teenagers typically need about 9 hours, and that slowly decreases over your lifetime. Older people usually need about 7 hours. Of course, sleep requirements differ for different people, just like, say, nutritional requirements, but people tend to underestimate their needs. It is believed that 80% of college students are seriously sleep deprived!

The consequences are clear: You become increasingly irritable; Your attention span, your memory, and your ability to learn things diminishes; You have an increased chance of accidents. Physically, you are more likely to develop blood pressure and heart problems; Your immune system's effectiveness diminishes; And you age more quickly, ending with a shorter lifespan!

Some people seem to have a hard time getting the sleep they need. This is called insomnia, and from 10 to 15% of the population suffers from it at any one time. For most people, the causes are not hard to find: Too much stress and anxiety; too much caffeine (found in coffee, tea, chocolate, and many soft drinks); other stimulants; the REM rebound (excessive dreaming) effect that comes from using alcohol or sleeping pills; and the schedule changes involved in shift work, distance travelling, and daylight savings time. Most people who have insomnia can find significant relief if they address these issues!

An extremely rare disorder -- .05% of the population -- is narcolepsy. This is a neurological problem that causes the person to suddenly fall asleep at odd moments, sometimes frequently throughout the day. This may sound amusing, but it is in fact both dangerous and debilitating.

Not so rare -- 4% of the population, including myself -- is sleep apnea. Apnea means "not breathing" during sleep, which is, as you can imagine, not a good thing. People with sleep apnea can stop breathing as many as 600 times a night. When that happens, the brain wakes up, the person gasps for air, and then falls asleep again. This means that you get very little deep sleep, if any, and the effects are similar to the ones mentioned for lack of sleep above. After a while, people with sleep apnea begin to fall asleep during the day at highly inconvenient times, such as while driving. It is also thought to be a leading immediate cause of night-time heart attacks.

A particularly handsome sleep clinic patient
wired for sound

Although some sleep apnea is, like narcolepsy, a matter of neurology, most of it has to do with the throat: Most people with sleep apnea snore. Snoring happens when the back of the palate slips back into the throat and partially blocks the airways. The sound is due to the rapid vibrating of the palate. For some people, this is due to genetics, for others to obesity. While snoring is not necessarily a dangerous thing (outside of potential homicide by spouse), it can develop into sleep apnea.

Typically, people with sleep apnea go to a sleep clinic, where they are monitored with EEG and other devices, to determine the extent of their problem. They are then fitted with a device called a CPAP machine (for "continuous positive airway pressure"), which essentially blows air into your nose to keep the air passages open at all times. Some people prefer to have operations that involve removing the uvula and stiffening the soft palate by scarring it. This doesn't always work well, so the CPAP machine is generally recommended instead.

Dreams

As we come closer to wakefulness during these cycles, we are able to develop memories of the random firings of neural restoration, just as we would be of perceptual events if we were completely awake. Perhaps the hippocampus, which is responsible for translating memories from “working storage” into “long term storage” (from immediate awareness into memory). And so we are aware of these sequences of firings, and remember the experience well enough to relate them to our friends.

It has been an idea for a very long time that dreams have special meaning. Freud, of course, made this a centerpiece for his therapy. He distinguished between the manifest content (the apparent or surface meaning) and the latent content (the deeper, symbolic meaning), and he believed that a psychiatrist could interpret dreams to discover a patient's deepest needs and concerns, ones that would be too uncomfortable to confront, even in one's dreams!

Over the last century, though, we have become quite skeptical of this idea. I am basically skeptical, and sometimes refer to dreams as “brain poop,” also known in more professional circles as day residue. But, I would add that dreams often seem to center around our "issues" -- and thereby can provide us with some leads as to what our issues are.

If one dreams about anxiety-provoking things, it seems reasonable to believe that you are suffering from anxiety. If there are certain scenarios in your dreams that cause you that anxiety, perhaps those are issues for you. I, for example, frequently dream about being criticized or evaluated or humiliated in front of an audience. That certainly makes sense for me. I also dream quite a bit about moving from one house to another. Although I have lived in my present home for over 30 years, as a kid I moved frequently. So my dreams make sense, not only as day residue, but as indicators of my psychological history.