Chapter 16. The dream
I
Sleep is the most mysterious thing we do. We know it is vital; We just ignore exactly why. We cannot say for sure what the dream is for, what is the right amount for maximum health and happiness, or why some people fall into their arms easily while others perpetually struggle to achieve it. We dedicate a third of our life. At the time of writing these lines, I am sixty-six years old: in practice, that means that I have been sleeping everything we have been of the 21st century.
There is no part of the body that does not benefit from sleep or does not suffer from its absence. If they deprive us of it for long enough, we will die, although it is also a mystery what exactly kills us when we do not sleep. In 1989, in an experiment that is unlikely to be repeated given its cruelty, a group of researchers from the University of Chicago kept 10 rats awake until they died; it took between 11 and 32 days for the exhaustion to overcome them deadly. Autopsies showed no abnormality that could explain his death: their bodies simply gave up.
Sleep has been associated with numerous biological processes, such as consolidating memories, restoring hormonal balance, emptying the brain of accumulated neurotoxins and readjusting the immune system. In one study it was found that a group of people with initial signs of hypertension who started sleeping each night an hour more than before showed a significant improvement in their blood pressure readings. In short, then, the dream seems to be a kind of nocturnal set-up of the body. As he declared in 2013 to the magazine Nature Loren Frank, of the University of California in San Francisco: «The story everyone tells is that sleep is important to transfer memories to the rest of the brain. The problem is that there is basically no direct evidence of that idea. But so far we have not known how to respond to the question of why, to do that, we must be forced to renounce consciousness in such a full and absolute way. It is not only that when we sleep we are disconnected from the outside world, but that for most of the time we are paralyzed.
The dream is obviously much more than a mere rest. A curious fact is that animals that hibernate also have periods of sleep. That may be surprising to most of us, but the truth is that hibernation and sleep are not the same, at least from a neurological and metabolic perspective. Hibernating is more similar to being shocked or anesthetized: the subject is unconscious, but not properly asleep. So an animal in hibernation needs a few hours a day of conventional sleep within its general state of unconsciousness. Another surprising fact for most of us is that bears - the most famous winter sleepers - don't really hibernate. Authentic hibernation implies a profound unconsciousness and a drastic decrease in body temperature, often around 0 ° C. According to this definition, bears do not hibernate, since their body temperature is maintained at levels close to normal and they also wake up easily. It is more appropriate to qualify your winter dream as a state of lethargy.
Whatever the dream gives us, it is more than a mere period of restorative inactivity. There has to be something that leads us to ardently crave to be at the mercy of possible attacks by bandits or predators; However, as far as we know, sleeping does nothing for us that could not be done equally while awake, but at rest. Nor do we know why we spend much of the night experiencing those surreal and often disturbing hallucinations we call dreams. Being chased by zombies or being inexplicably naked at a bus stop does not seem, at first glance, a particularly restorative way to spend hours of darkness.
And yet, there is a universal belief that the dream must respond to some deep elementary need. The eminent sleep researcher Allan Rechtschaffen observed it many years ago: "If the dream does not fulfill an absolutely vital function, then it is the biggest mistake the evolutionary process has ever made." However, as far as we know, the only thing that makes the dream is (in the words of another researcher) "prepare to be awake."
It seems that all animals sleep. Even creatures as simple as nematodes and fruit flies have periods of inactivity. The amount of sleep needed varies considerably from one species to another. Elephants and horses sleep only two or three hours each night. It is unknown why they need so little, since most other mammals require much more time. It is still said that the animal that was considered the champion of sleep among mammals, the three-toed sloth, sleeps up to twenty hours a day; but that figure comes from the study of lazy captives, who have no predators or too many things to do. The wild sloths, on the other hand, sleep around 10 hours a day, not much more than us. An extraordinary fact is that some birds and marine mammals can turn off only half of their brain alternating between them, so that one half remains alert while the other dozes.
The origin of our modern understanding of sleep can be found on a night in December 1951, when a young researcher at the University of Chicago who studied matter, Eugene Aserinsky, tested a machine to measure the brain waves that his laboratory had acquired. Aserinsky's volunteer subject for that first test night was Armond, his eight-year-old son.
Ninety minutes after little Armond had plunged into what was usually a peaceful night's sleep, Aserinsky was perplexed to see that, suddenly, the millimeter paper roll of the monitor came to life and began to draw the type of strokes irregularities normally associated with an active and awake mind. When Aserinsky entered the room, he discovered that Armond was still sound asleep but his eyes were visibly moving under the eyelids. Aserinsky had just discovered what would become known as a dream of rapid eye movements, the most interesting and mysterious of the multiple phases of our nightly sleep cycle. It cannot be said exactly that Aserinsky ran to publish his results: it was almost two years before a small report on the discovery appeared in the journal Science. *
* Aserinsky was an interesting guy, although extremely restless. Before arriving at the University of Chicago in 1949, at the age of twenty-seven, he attended two other universities and studied successively studies in sociology, preparation for medicine, Spanish and dentistry, without completing his studies in any of these subjects. In 1943 he was recruited by the army, and, despite being blind in one eye, he spent the war as an expert in explosives deactivation.
Today we know that a normal night's sleep is divided into several cycles, each of which consists of several phases (four or five, depending on the preferred method of classification). First comes the stage of renouncing consciousness, something that most of us take between five and fifteen minutes to achieve completely. This is followed by a period in which we have a light but restful sleep, as in a nap, for about twenty minutes. In these first two phases, the dream is so superficial that, in fact, we may be asleep but believe that we are awake. Then comes a deeper sleep, which lasts about an hour, from which it is much more difficult to wake the sleeper (some experts in turn divide this period into two stages, which gives the sleep cycle a total of five distinct phases instead of four). Finally comes the phase, already mentioned, of rapid eye movements (abbreviated MOR, or more frequently REM, for its acronym in English), which is when we experience most of our dreams.
During the REM phase of the cycle, the sleeper remains practically paralyzed, but the eyes experience small rapid movements below the closed eyelids as if they were witnessing a pressing melodrama, while the brain is as active as at any time during the vigil. . In fact, some parts of the forebrain are more alive during REM sleep than when we are fully aware and walking from side to side.
We do not know for sure what the eye movements of REM sleep are due to. An obvious idea is that we are "visualizing" our dreams. Not our whole body is paralyzed during this phase. The heart and lungs continue to function for obvious reasons, and it is also clear that the eyes have freedom of movement; but all the muscles that control body movement are constricted. The explanation that is most frequently postulated is that immobilization prevents us from harming ourselves by throwing blows or trying to flee an attack when we are caught in a nightmare. A very small number of people suffer from a condition called REM sleep behavior disorder, in which the limbs do not become paralyzed, and, in fact, sometimes hurt themselves or their partner by beating. In other cases, the paralysis does not remit immediately upon waking, and the victim is awake but unable to move; apparently a deeply disturbing experience, but fortunately it tends to last only a few moments.
The REM phase covers up to two hours of each night of sleep, approximately one quarter of the total. The periods of REM sleep tend to lengthen with the course of the night, so that when we dream the most it is usually in the last hours before waking up.
Sleep cycles are repeated four or five times a night. Each cycle lasts about 90 minutes, but its exact duration may vary. It seems that REM sleep is important for development. Newborn babies spend at least 50% of their sleep hours (which in any case is most of the day) in this phase, while fetuses can reach up to 80%. For a long time it was believed that all of our dreams came during the REM phase, but a study conducted in 2017 at the University of Wisconsin found that 71% of people dreamed during the non-REM phase (compared to 95% who did so during the REM phase). Also, most men have erections during this phase, while, similarly, women experience increased blood flow in the genitals. No one knows why that happens, but it does not seem to be clearly associated with erotic impulses. As a general rule, nocturnal male erections are extended for a period of about two hours.
At night we are more agitated than most of us think. A normal person, on average, turns around or significantly changes his position between 30 and 40 times during the night. We also wake up much more than we think. The moments of alert and brief awakenings that we experience during the night can add up to a total of 30 minutes without us being aware of it. On a visit to a sleep clinic he made in order to document himself for his book Night , published in 1995, the writer A. Álvarez had the impression that he had experienced a night of uninterrupted sleep, but when reviewing his chart in the morning He discovered that he had actually woken up 23 times. He had also had five periods in which he had dreamed, despite which he did not remember any of those dreams.
In addition to normal nighttime sleep, we also allow ourselves to give the occasional brief nod during waking hours, in a state known as hypnagogy, a dark region midway between wakefulness and unconsciousness, often without realizing it. In an alarming discovery, when a team of sleep scientists studied a dozen airline pilots who made long-haul flights, it turned out that almost everyone fell asleep, or almost asleep, at one time or another of the flight without being aware of it.
The relationship between the sleeper and the outside world is usually curious. Most of us have experienced while we sleep that abrupt feeling of tripping and falling known as hypnotic shaking or myoclonic spasm. No one knows why it happens to us. One theory postulates that its origin dates back to the times in which we slept in the treetops and should be careful not to fall. The jolt could be like a kind of fire drill. This may seem somewhat exaggerated, but it is still curious, if you think, that no matter how deeply unconscious, or agitated, that we are, we almost never fall out of bed, even when we sleep in beds with which we are not familiar like those of hotels and the like. We may be dead to the world, but there is some sentry inside us that takes note of where the edge of the bed is and does not allow us to roll beyond it (except in extreme circumstances conditioned by alcohol or fever). It seems, then, that a part of us continues to pay attention to the outside world even in the case of those who sleep more deeply. Several studies conducted at the University of Oxford and commented by Paul Martin in his book Counting Sheep found that the electroencephalogram needles of test subjects fired every time their own name was spoken out loud while they slept, but did not react when other names unknown to them were recited. Other tests have also shown that people are quite good at waking up at a predetermined time without the need for an alarm clock, which means that some part of the sleeping mind must be tracking the real world beyond the skull.
Dreams may be just a byproduct of our nocturnal cerebral "cleansing." While the brain removes waste and consolidates memories, the neural circuits are activated randomly producing brief fragmentary images, something similar to when we jump from one television channel to another looking for something to see. Faced with this incongruous flow of memories, anxieties, fantasies, repressed emotions and others, possibly the brain tries to build a coherent story, or it is also possible, given that it is resting, that it does not try at all and is limited to letting all those flow unconnected pulses That could explain why we don't usually remember dreams too much despite their intensity: because, in reality, they are neither important nor significant.
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Author: Bill Bryson
Publisher: RBA
Translator: Francisco J. Ramos Mena
Format: 512 pages. 20 euros.
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