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The Brain During Sleep

Jump to the following topics:

  1. The stages of sleep. 
  2. REM sleep.  
  3. Non-REM dreams. 
  4. The brain during a dream. 
  5. The information-processing function of dreams.   


The stages of sleep. While we sleep, we go through a series of stages which differ in their brain-wave patterns and physiological conditions.

  1. When we first enter sleep, our brain waves decelerate from beta (12 to 18 cycles/second) to alpha (8 to 12 cycles/second) to theta (4 to 8 cycles/second). At this point, stage one begins.
  2. The stages.
    • Stage one. This stage lasts for only a few minutes of light sleep. We experience a lowering of body temperature and blood pressure, relaxation of our muscles, and a slowing of our breathing and heart rate. Brain waves are slow and low-voltage. The first "stage one" of the sleep period is called "descending stage one."
    • Stage two. We are now in a deeper sleep, and more difficult to awaken. Our muscles relax. Stage two is recognizable by its predominance of theta waves and the appearance of "sleep spindles" (momentary occurrences of high-voltage brain waves at 12 to 14 cycles per second) which occur only during this stage.
    • Stage three. During stage three, we become more relaxed, and we experience a decrease in heart rate, body temperature, blood pressure, and respiratory rate. Our brain waves are increasingly within the delta range (1 to 3 cycles per second).
    • Stage four. We spend about 20 minutes on this level, which is characterized by profound muscle relaxation, difficulty in awakening, and a majority of our brain waves within delta. When we leave stage four, we ascend through stage three and two and one. As the cycle continues throughout the sleep-period, stage four becomes shorter -- and by the end of the night, we are alternating only between stage two and stage one. Stage four is experienced only two or three times during our sleep period.
    • Ascending stage one. (Also called "emergent stage one.") We return to stage one approximately 90 minutes after entering sleep. Unlike the first stage one, this is a period of rapid eye movements and REM dreaming. (Non-REM dreams can occur at any time during sleep.) The first time we enter "emergent stage one," the period continues for only about five to ten minutes before we descend again to stage two and so on; by the end of the night, stage one might continue for as long as one hour -- for a total of approximately 90 minutes of REM throughout the sleep-period. REM sleep consists of two stages; "phasic" is the time of muscle twitching, quick eye movements, fast heart rate, and lucid dreams -- and "tonic" is a quieter interval.
  3. The cycle continues. We continue a 90-minute cycle throughout our sleep period. Some researchers have speculated that a similar 90-minute cycle persists during wakefulness, with corresponding variations in brain activity and attentiveness; during the part of this wakeful cycle which corresponds to REM, we are in a less-attentive, daydreamy mood, as the brain seems to go off-line to process our new data. These two types of functioning (correlating to non-REM and REM) are similar to the analytic operations of the brain's left hemisphere and the creative reverie of the right hemisphere.


REM sleep.

  1. REM deprivation. In lab experiments, subjects have been awakened at the beginning of each REM period, thereby depriving them of REM sleep (although they were permitted to have non-REM sleep). After a few nights, some of the people exhibited psychological disturbances such as irritability, anxiety, disorientation, paranoia, inability to concentrate, acute hunger, depression, and decreased motor skills. (However, other people had virtually no adverse reactions to REM deprivation.) Animals in similar REM-deprivation experiments have become hypersexual; others have died. During experiments, some human subjects responded in these ways:
    • Some people would re-enter REM quickly after returning to sleep; even if they were awakened dozens of times, they would still attempt to achieve REM sleep. One researcher found that if the subject remained awake for three minutes after being disturbed from REM sleep, that period would be skipped, and the four-step sleep cycle would start at the beginning. In another experiment, the standard 90-minute sleep cycle became shorter, as if to return the sleeper to emergent stage one -- where REM dreaming occurs -- as quickly as possible.
    • Their non-REM dreams became weirder, as though trying to behave like REM dreams. Non-REM dreams are usually similar to plain "thinking," while REM dreams are strange, story-like creations.
    • They hallucinated during wakefulness. This might be another way in which the demand for "dreams" imposes itself (in the form of hallucinations) onto time which is normally not set aside for dreams.
    • Their sleep became lighter, as though they were trying to remain close to stage one where REM dreams occur.
    • When the experiments ended, they would spend nearly all of their sleep-time in REM. This was apparently an attempt to compensate for the deficit.


Non-REM dreams. Although dreams are usually associated with REM sleep, the correlation is not exact; dreams do occur during non-REM periods, and people who are awakened from REM sleep frequently do not report dreams. Some non-REM dreams are similar to REM dreams (and vice versa), but they usually exhibit these differences: non-REM dreams tend to resemble wakeful thinking (perhaps pondering a wakeful event, or a REM dream which has occurred), and they are generally less emotional, outlandish, lengthy, dramatic, visual, and active. When people are awakened from non-REM dreams, they might say that they weren't asleep at all, but were awake and thinking; this is the error made by some people who claim to be insomniacs, although sleep-lab equipment proves that they were sleeping. In one occasion when I recalled the non-REM state, I noted that "the thoughts were the same as ordinary daytime thoughts, and they concerned regular subjects. It was just an ordinary 'mulling over.'"


The brain during a dream.  

  1. During dreamless sleep, the brain operates on a subdued level -- just enough to maintain its basic functions and the body. But during a dream, it becomes more active. During REM sleep, our brain has a higher temperature and increased blood flow. The brain waves are irregular with extreme peaks and troughs; they can be described as mixed frequency waves, with low amplitude, and only slight alpha activity.
  2. Part of the brain might consider our actions to be "real." When we dream of performing an activity (e.g., running), the brain sends the same signals that it would send if we were awake and running. To that part of the brain and nervous system, we are running; hence, the dreamed experience seems authentic. However, during REM sleep, these nerve impulses are obstructed before they reach the muscles, through a function called "sleep paralysis." This paralysis keeps us from acting out our dreams while asleep. (In an experiment, cats were given a drug which counteracted sleep paralysis; during dreams, they ran, pounced, and hissed in apparent interactions with feline-dream characters -- perhaps mice or other cats.)
  3. Our sensory perceptions might seem to be "real." During wakefulness, our imagination is active, adding emotion and fantasy to everything which we perceive. However, these fancies are usually overpowered by sensory input, and they are suppressed by serotonergic neurons. During REM sleep, we receive no sensory input, and those neurons are constrained. Thus our imagination is free to express itself -- and it does so through the same neural network which would be feeding sensory input to the brain if we were awake. If we see, for example, a tree during a dream, the neurons react in the same manner as if they were seeing a wakeful-world tree. For their purposes, the dreamed tree is "real."
  4. EEG readings during REM sleep. When a person is awake and attentive, brain waves are spiked and short. Tiredness causes the brain waves to become slow and long; the REM period puts the waves back into a short pattern -- mixed frequency, low amplitude. EEG readings become more animated as the person shifts from deep sleep to dreaming. During the first half-minute of REM, alpha waves decrease in the left parietal region of the brain; as when we are awake, alpha rhythms are less prominent during vigorous periods than during calm periods, so this reduction in alpha indicates an enlivening of the brain. While the dream is occurring, the level of EEG activity varies according to the amount of commotion in the dream; during energetic dreams, the brain is more active than during wakefulness, and the EEG reading is virtually indistinguishable from that of wakefulness. Alpha rhythms are more conspicuous when the dream scenario is passive than when it is busy.
  5. The brain during REM sleep. REM begins when the GTF (gigantocellular tegmental field) neurons in the pons (bridge) of the brain stem are stimulated. These GTF nerve cells excite the lower brain (the seat of emotions) and the cortex (where sensory data -- including visual data -- is processed). During REM, the brain emits neurotransmitter chemicals: large amounts of acetylcholine (which stimulates the cortex), and small amounts of serotonin and norepinephrine. At the end of the REM period, dreaming ceases when the locus coeruleus (another cluster of cells in the brain stem) emits another neurotransmitter, norepinephrine, to deactivate the GFT cells. In an experiment with a cat, the EEG readings which correspond to REM sleep were induced by a drug which is similar to the acetylcholine; those readings returned to a non-REM status when the cat was given a dose of norepinephrine.


The information-processing function of dreams.  

  1. While we sleep, one of the brain's tasks is to process information which was acquired while we were awake.
  2. Dreaming is "off-line processing." When a computer has to catch up on a backlog of data, we make it go "off-line"; we disconnect it from sources of additional data until the backlog is consumed. Sleep offers us a similar situation; this is a time when we are not gaining new experiences, physical challenges, or sensory input. Another advantage is that the unconscious mind can review our wakeful life without the interference of the conscious mind's rigid style of reasoning, limited creativity, habitual patterns of thought, and restricted access to psychological and spiritual resources which are available to the unconscious mind. (However, during subsequent wakefulness, the conscious mind's logical and intuitive faculties must decide whether the unconscious mind's proposed solutions are likely to be appropriate and effective in the wakeful world.)
  3. Memories are processed during sleep. Many studies have shown that sleep (and dreams in particular) are necessary for the workings of our memory. Consider these experiments, from which we might make the following conclusions:
    • REM sleep is better than non-REM sleep for recall. Subjects were awakened from sleep and asked to remember some material. When they awoke again, they were re-tested. The people who had exhibited more REM sleep remembered more. (This effect is more noticeable when the material is an abstract mental skill than it is when the subjects engaged in simple memorization.) In a different experiment, some students were awakened during various stages of sleep; if awakened from non-REM sleep, they continued to progress in a skill which was being studied during wakefulness -- but if they were awakened from REM sleep, they did not progress.
    • REM sleep is better than wakefulness for recall. Subjects were asked to remember some information, and they were retested later; during the intervening period, some of the people slept and the others stayed awake. If the sleep period was two hours or less, the sleepers and wakefuls lost the same amount of recall. But if the sleep period was more than two hours, the sleepers remembered the same amount as if they had been awakened after two hours; however, the wakefuls continued to forget more of the data as time went on.
    • REM sleep is more effective for recall of emotional material. Subjects were tested on their skills in concluding a story and a crossword puzzle; after REM sleep, they showed a greater increase in their abilities with the story than with the crossword puzzle. (A story deals with the emotions of the right hemisphere; a crossword puzzle involves the logic of the left hemisphere.)
    • REM sleep increases during periods of learning. When rats were learning to run a maze, they had more REM sleep than they had had before starting their lessons. When infant humans are asleep, about 50% of their time is spent in REM (probably to process the profusion of data from their new world); adults spend only 20% to 25% of their time in REM.
    • Dreaming also affects our types of wakeful memories. In an experiment, people were tested on their ability to remember a list of words. Some of the people were deprived of dreams during the sleep period preceding the experiment; they remembered more words pertaining to emotions and introspective themes. The people who had dreamed normally remembered more words relating to social interplay and personal accomplishment; we might conclude that they had worked out their inner needs during dreams and were now ready for the challenges of the wakeful world.
  4. We spend more time dreaming when confronted with problems. We process not only memories but also speculations on problem-solving. We dream more, and sleep longer (probably so that we can dream more), during phases when we encounter stress or emotional disturbance from situations such as a new job, or family turmoil, or a school examination.
  5. We consider and rehearse alternatives during dreams. Nietzsche said that dreams are a training ground for life. During dreams, we frequently mock up circumstances which have disturbed us in wakefulness: we see (perhaps symbolically) those perplexing people and circumstances. A dream character is created to represent a troublesome individual, and then our dream persona experiments with different behaviors which might resolve our distress. If this process is successful, we discover a solution and we might also relieve some of the stress which was related to the problem. (For example, pregnant women who dream about their delivery tend to have an easier delivery, probably because of their sleepful "rehearsals.")
  6. A dream speculation might be recognized when we are awake. During wakefulness, if the event which transpires resembles one of our previous speculative dreams, we might call the dream "precognitive," and the event might be accompanied by a deja vu feeling (because it did happen before -- in a dream). However, in some supposedly precognitive dreams, we are merely speculating, as indicated by the "death dreams" of ill people who recover.

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