Understanding Sleep

Sleep is a normal human phenomenon - a natural and very necessary part of our daily lives. It is so essential that, if denied it, we feel unwell and perform poorly, and eventually, no matter how hard we try, we simply must surrender to its power.

Aristotle, a Greek philosopher who lived three hundred years before Christ, proposed a theory to explain our universal need for sleep. He believed that food, once ingested, released vapors through the process of digestion. These vapors, being warm, rose to the brain and produced the sleepiness that so often follows a heavy meal. After some time, the vapors cooled down, allowing the brain to wake. What he was postulating is that the body produces some sort of chemical that causes sleep. Such a chemical (called a "hypnotoxin") has for centuries been suspected to be the cause of sleepiness. The substance would be produced in the body by exercise and wakefulness, and when it reached a certain critical level in the brain it would induce sleep.

Researchers tried to see if such a chemical existed by taking samples of blood from a sleeping animal and then injecting that blood into an animal who was awake, to see if the injected blood would produce sleep - it wouldn't. Nothing happened. Siamese twins, babies who have not developed in the uterus as separate entities, often share a single organ, such as the liver or the heart, and, though they have the same blood circulation, can have independent sleep-wake schedules - when one of the twins is sleeping, the other may be awake. 

These observations imply that there is no single hypnotoxin that causes sleep. The answer is not that simple. 

It took a Viennese neurologist to solve the mystery. 

Constantine Von Economo was a young volunteer officer in the Austrian Air Force during the First World War, assigned to the medical corps. During the terrible influenza epidemic of those years, he noted that many soldiers infected by the influenza virus were unable to stay awake. Autopsy showed that the virus damaged a specific part of the midbrain, the small bulbous extension of the top of the spinal cord, which lies just at the base of the skull. 

Curiously, some of the infected soldiers had exactly the opposite symptom - they couldn't go to sleep at all. Almost all these men died, and autopsy uncovered similar damage in the midbrain with only one difference - those with insomnia always had damage in the back or posterior part of the midbrain, and those who were unable to wake up had damage in the front or anterior part of the same structure. In attempting to explain the conflicting symptoms, Von Economo postulated that two separate centers existed in the brain - one that was responsible for sleep and another, beside the first, that was responsible for wakefulness. 

We now understand that there are two distinct centers for consciousness, both located deep in the base of the brain. One center controls wakefulness, the other sleeping. Both are active at all times, but their activity varies. With sensory stimulation and signals from the more developed parts of the brain, the wakefulness center predominates, and the brain "wakes up." Sometime later, when sensory stimulation and input from the other parts of the brain decrease, the sleep center becomes more active and sleep occurs. This duality is common in the human body and is critical in understanding the complexity of sleep. Usually, the alertness center is dominant, more powerful than the sleeping center. This makes sense from an evolutionary point of view: because we are vulnerable during sleep, conditions must be just right to allow the weaker sleep center to take control. The alert center, which keeps us in our normal waking state and able to defend and protect ourselves, is active most of the time, and relinquishes control to the sleep center only when conditions are appropriate.

Suppose you haven't slept well the night before, and you have to attend a boring lecture in the afternoon. The hot, stuffy room, the tediously dull topic, the comfortable chair you are sitting in, and the poor sleep you had the night before make chances very good that your sleep center will become more active and you may begin to nod off. However, in the same comfortable chair, at the same lecture, if you were asked to express an opinion on the boring topic, your wake center would take over, and all thoughts of sleep would be banished. You would be able to respond to the question, your mind fully alert and reasoning properly. Some minutes later, the two centers may have changed their roles again. It's like a balance of power - one center simply becomes able to dominate the other for a time. 

In general, then, insomnia is a state of imbalance - the center for alertness simply overpowers the center for sleep, preventing the latter from producing the restful effect that is so essential for a peaceful night's sleep. 

The alert center also responds (and this is an important concept for many people who have difficulty sleeping) to the brain's own thought processes, independent of the external environment. Even when you are lying in a darkened, quiet bedroom, where there is very little in the way of external stimulation, the alertness center can be stimulated by your own thoughts; if they are exciting or worrisome, they can act as stimuli for the awake center just as effectively as can bright light, sound, or other external factors, with the result that sleep is impossible.