Dreaming LifeDreaming Life

The wake up hypothesis of REM sleep was developed by W.R. Klemm of the Department of Veterinary Integrative Biosciences at Texas A&M University.  Klemm explained this hypothesis in an article that was published in September 2011 in Frontiers in Systems Neuroscience.

The wake up hypothesis of REM Sleep says that REM sleep and dreams help to prepare our brains to return from deep sleep to waking consciousness.

Coevolution of Deep Sleep and REM Sleep

During deep sleep, also known as Stage N3 sleep, the sleeper loses awareness of the external environment and cannot be awakened easily.

When a person is in deep sleep, their brains produce high voltage slow waves. Therefore, this sleep stage is sometimes known as slow wave sleep.

REM sleep, or rapid eye movement sleep, is a stage of sleep that, in humans, is associated with vivid dreams.   During REM sleep, there is an increase in metabolic activity.  Low voltage brain waves are produced.

Klemm believes that deep sleep and REM sleep evolved together.

All mammals, birds and some reptiles, experience sleep cycles in which N3 sleep is followed by REM sleep.

All higher mammals experience sleep cycles similar to the human sleep cycle.

Lower mammals, birds and a few reptile species are known to experience short periods of REM

Fish and amphibians, on the other hand, experience neither N3 sleep nor REM sleep.

Sometimes, fish and amphibians seem to be in a state of deep sleep. However, during these periods, their brains do not generate the slow waves that would be produced by a mammal in N3 sleep.

Klemm noticed that there is often a direct relationship between the amount of deep sleep and the amount of REM sleep that each type of animal experiences.

For example, mammals, such as ruminants, that are prey for other animals, spend much less time in N3 sleep then predators, presumably because they must constantly be on the alert for predators. Prey animals also have much less REM sleep than predators.

Dangers of Too Much Deep Sleep

It is known that mammals need deep sleep in order to survive.

There are a number of different possible explanations for why deep sleep is necessary. N3 sleep may help conserve energy, help to restore the function of physiological systems that are depleted during waking hours, help to restore physiological balance and/or have a role in thermal regulation.

Deep sleep is believed to be a time for growth and regeneration.

Nevertheless, deep sleep can't go on forever.  If you spent all your time sleeping, eventually, you would die of dehydration and malnutrition.

As Klemm points out, deep sleep is so dangerously "deep" that in people with sleep apnea, the breathing reflexes actually stop.

You need deep sleep, but you also need to wake up.

Waking Up

During deep sleep, all the neural connections in the brain that are used to create and maintain consciousness are obliterated.

To wake up and become conscious, these neural connections have to be restored. The neural networks that provide you with your sense of self and the memory of who you are have to be reorganized.

In order for your neural connections to be restored, so that you can wake up, you're ascending reticular arousal system (ARAS), which is located in your brainstem, has to be activated. Once your ARAS is activated, it stimulates your brain's neocortex, which is associated with higher levels of thinking, to make you awake and conscious.

The ARAS is activated by sensory input and by thinking.

That is why you can be awakened by a loud alarm clock or by someone shaking you and why you find it difficult to fall asleep when you're reading an exciting book or when you have a lot on your mind.

REM - A Transitional State Between Deep Sleep and Waking

Klemm believes that REM sleep is a transitional state between N3 sleep and waking consciousness.

REM sleep is similar to waking consciousness.

For example, during REM sleep, you have dreams in which you appear to be conscious.  In your dreams, you observe things and do things just as you would in waking life.

Klemm says that the reason why dreams can be so bizarre is that in a dream, you aren't getting feedback from the outside world, as you do when you are awake and conscious.

Overall, the brain is relatively inactive during N3 sleep.  During REM sleep, the brain is reactivated. In some areas, the brain is more active during REM sleep than during wakefulness.

An increase in acetylcholine in the brain's cortex during REM sleep can be associated with a movement toward consciousness.

During REM sleep and during quiet waking, there is a 100% increase in acetylcholine in the cortex, as compared with the amount in the cortex during deep sleep.

There is a 175% increase in acetylcholine during active waking as compared with deep sleep.

We Naturally Wake Up During REM Sleep

Although you can wake up to the sound of an alarm clock or the sound of your neighbor hammering next door, waking up to an external cue doesn't reflect the natural sleep cycle. In fact, when you wake up this way, you are often groggy and disoriented, and it takes a while for you to be truly awake. (The brain circuitry that keeps you conscious hasn't been fully reorganized.)

On the other hand, says Klemm, when people wake up without any external stimulus, they tend to wake up from REM sleep, either during a dream or at the end of a dream.

The content of the dream might be just what is needed to stimulate the ARAS and create wakefulness.

REM Sleep Increases Throughout the Night

Normally, you only experience REM after you have had a long period of N3 sleep.

The length and frequency of periods of REM sleep increase as the night goes on.

According to Klemm, this could because the brain is slowly "learning" how to wake itself up.

The shorter REM episodes that take place early in the night could be the brain's initial attempts to create a conscious state.

As the night goes on, and the brain gets more "practice", its ability to wake itself up improves.

If there is no external stimulus to wake you (no loud alarm clock or noisy neighbor), it can take all night for the brain to figure out how to wake itself.

Sometimes an external stimulus wakes you up in the middle of the night, when you haven't had enough sleep. When you go back to sleep, you dream some more. This indicates that your brain hasn't yet been able bring about the full wake-up effect of REM sleep.

Lucid Dreaming

Brain activity during lucid dreaming is even closer to waking state brain activity than brain activity during "normal" REM sleep is.

Klemm suggests that lucid dreaming might be a way to bring some of us even closer to the waking state before we actually awaken.

Dreaming and Age

According to Klemm, his wake up hypothesis explains why REM sleep decreases with age.

Fetuses and infants experience much more REM sleep than older people.

Infants spend about half of their sleeping time in REM, while adults spend only about one fifth of their time in REM.

This noticeable decrease in the proportion of sleep time spent in REM is found in all species that experience both N3 sleep and REM.

According to Klemm, the brains of fetuses and infants have to develop rapidly. During REM sleep, neural activity is heightened.   The neural activity of fetuses and infants must be heightened more frequently in order for brain development to be sped up.

The young, developing brain might spend more time in REM because it has to learn how to wake itself up. It might be very hard for the brain of a fetus or infant to bring itself out of deep sleep.

Klemm notes that very young babies spend most of their time sleeping.   A tiny infant wakes up only when it perceives an external stimulus, for example, if it is hungry or if its diaper is wet.  REM trains the young brain to achieve consciousness without external stimulation.


People who suffer from clinical depression experience more REM sleep than people who are not depressed. Klemm suggests that this might be because it is more difficult to arouse a depressed brain.

REM Deprivation

It is known that if people are deprived of REM sleep, they make it up later on.

Klemm says that when you wake up because of an external stimulus, the brain doesn't go through the same REM rehearsal process that it needs to wake itself up.

The brain creates extra REM sleep the following night in order to finish the natural waking process.

People who are deprived of REM sleep do awaken from sleep, so at first, it may appear that REM sleep is not necessary for waking.

However, REM sleep deprivation occurs in experiments in which the subject is artificially awakened so that he or she does not fall into REM sleep. The jostling of the sleeper by the experimenter causes the awakening. This is not the natural awakening that comes from REM.

Difference Between Dreams and REM Sleep

Klemm's wake up hypothesis of REM sleep implies that dreaming is an integral part of REM sleep.  The mental activity that takes place in dreams, in which you have a sense of who you are, and in which you sense things and do things, is very similar to the mental activity that takes place when you are awake.  The mental activity that takes place in dreams, like the mental activity that occurs during wakefulness, stimulates the ARAS.

However, studies have shown that REM sleep and dreaming are not the same thing. For example, dreaming can occur in NREM sleep (non-rapid eye movement sleep - the other sleep stages).

Klemm argues that NREM dreams only take place in the lighter stages of NREM sleep; they do not occur during deep, N3 sleep.

Besides, it's not the dream itself that wakes you up. It's the fact that the dream stimulates the ARAS, which then stimulates the neocortex. The neocortex then creates consciousness.