In 2009, J Allan Hobson introduced the idea that dreaming enables us to develop consciousness. Hobson said that during REM sleep, you create a virtual world that prepares your brain for dealing with the real world.
In a 2012 article in the journal Progress in Neurobiology, Hobson and Karl J Friston expanded on the idea of dreaming as a virtual reality generator. They attempted to explain why we create a virtual world during REM sleep, the characteristics of that virtual world, and how its structure affects the content of our dreams.
Hobson and Friston believe that during our dreams, we create a model of the world that we can use to test the consequences of our actions before we perform them in waking life.
This idea is similar to the evolutionary theory of dreams, which states that our primitive human ancestors evolved the ability to dream in order to learn how to deal with threats that they experienced in their waking lives.
Loss of Sensory Feedback During Dreaming
Sensory feedback from the external world is dampened during sleep.
In contrast, when you are awake, you are constantly getting feedback from your senses.
Your brain uses this feedback to help you create predictions about what you will experience in the future. As you experience things, your brain alters future predictions, taking the new knowledge that you have gained into account.
Hobson and Friston provide the example of feeling your way along the walls of a darkened room. You predict what you are going to feel along the wall before you take your next step. Then you take that step and you discover whether your prediction was correct. If it isn’t, you revise your ideas about what the room is like, and this affects your future predictions.
In another example of how you might use sensory feedback, suppose you hear what seem to be the sound of raindrops against your window. You predict that if you look outside the window, you will see that it is raining. When you look outside, it is raining and your prediction is confirmed.
Suppose, however, when you look outside, it isn’t raining. You then have to think about what else could be making that noise, and you have to revise your predictions about what that noise means.
Then, you must check on whether your predictions were correct.
So there is a continuous cycle of revising predictions, checking them and revising them again.
The problem with this way of learning about the world is that it makes determining what is going to happen in the future, and how you should respond to it, very complicated – and this makes it more likely that you will make mistakes.
A virtual model of the world – the kind that exists in dreams – has to be simple and has to use general concepts that don’t employ much detail in order for it to help you deal with many different possible situations that you might encounter in waking life.
The way your brain simplifies the virtual world of dreams is by almost completely eliminating sensory feedback when you sleep (although sometimes, sensory feedback can influence a dream – for example, if there is a loud car alarm outside and your dream interprets it as an air raid siren).
This means that you do not have to constantly revise the mental image of the world that exists in your dream, and your dreaming mind can focus more closely on dealing with whatever situations occur in the dream.
Generalization in Dreams
Characters and objects in dreams tend to be very generalized. This is because it is easier and more efficient for you to learn how to deal with a general case one time than to learn how to deal with many specific cases many times.
If the virtual reality model created in a dream were too specific, there would be many waking life situations that it would not cover and it would not be very useful.
One consequence of the fact that dreams utilize generalizations is that the objects and characters in dreams are often not exactly like people and things that you know in waking life.
Upon waking up from a dream, you may remember dreaming that you lived in a house. You may realize that even though you “knew” that it was your house while you were in the dream, it didn’t resemble your waking life house at all, and it didn’t resemble the houses of anyone you know, either.
This is because your dream house wasn’t an actual house – it was a representation of your concept of a house – like the picture of a house that you see next to the word “house” in the dictionary. It represents every house you have ever seen and every house that you will ever see.
Faces in dreams also often do not resemble the faces of people in waking life. You may dream about your brother, for example, and then wake up and realize that your brother’s face in the dream was not anything like your brother’s face in real life.
Often we do not see the faces of the characters in our dreams at all.
This is because a face adds unnecessary complexity to the character; in the dream, what is important is who or what the character represents, not the details of what the character looks like.
Given the bizarreness of REM dream content, we tend not to be as surprised as we should be.
In a dream, you might fight a pack of zombies, discover that you can fly, take a test in a school that you graduated from twenty years ago, and then give birth even though you weren’t pregnant when you went to sleep (or are a man).
While you might experience strong emotions in your dream, your reaction to these events in your dream will be nothing like the reaction that you would have if you were to experience any of these situations in waking life.
In dreams, you accept impossibilities like these without question.
An exception to this, which Hobson and Friston do not mention in their article, would occur during lucid dreaming. When you are having a lucid dream, you may recognize that something in your dream would be impossible in the waking world, and that therefore, you must be having a dream. Hobson has previously stated that lucid dreaming is a state that combines aspects of the dreaming state and the waking state.)
Hobson and Friston turn to information theory to explain the lack of surprise in dreams. Surprise, according to information theory, is the difference between what you discover has happened and what you predicted would happen. That is, the closer your predictions match what you later experience, the less surprised you are.
Information theory says that biological systems act on their environment in order to minimize surprise, which reduces the natural tendency of their environment to become more disordered (the natural tendency for entropy to increase.)
There are two possible ways to minimize surprise: You can change your predictions to match your experiences more closely, or you can change your experiences to match your predictions more closely.
When you are awake, it is very difficult to change your sensory experiences, because they are based on a reality that is external to you. The only way you can reduce surprise is by constantly changing your predictions of what you will experience, based on feedback from your senses.
This is a complicated process.
Your perception of the waking world constantly changes because you are constantly changing your view of the world based on things that you have experienced, in order to reduce the amount of surprise that you experience.
For example, suppose you never knew that women could ride motorcycles. The first time you see a woman ride a motorcycle, you are surprised because you did not think that such a thing could happen. After that, however, you alter your predictions about the possibility of women riding motorcycles, and the next time you see a woman on a motorcycle it is less surprising.
In dreams however, things work the opposite way. Your brain creates an internal world that immediately matches your predictions.
By eliminating sensory input from the external world during sleep, your brain does not have to deal with sensations that could interfere with the way you experience the virtual world of your dream.
You don’t experience surprise because you create the dream world that you predicted.
Friston and Hobson provide a neurological explanation for the lack of surprise in dreams by looking at PGO waves (pontine-geniculate-occipital system waves).
These are relatively large brainwaves that emanate from three places: the pons, a small structural in the brain stem; the lateral geniculate nuclei, which are found inside the thalamus; and the posterolateral cortex.
In the 1950s, PGO waves were discovered in cats that were experiencing REM sleep.
We now know that other mammals, including humans, also emit PGO waves.
The lateral geniculate nuclei are associated with vision, and scientists studying REM sleep in cats looked at the relationship between PGO waves coming from cats’ lateral geniculate nuclei and the cats’ eye movements during REM sleep.
The brain has two lateral geniculate nuclei – one on the right and one on the left. Researchers discovered that when a cat’s eyes moved to the right, the PGO wave coming from the right lateral geniculate nucleus shot up to twice the amplitude of the PGO wave on the left. When the cats’ eyes moved to the left, the opposite occurred.
When you are awake, the PGO waves that your brain produces are associated with unpredicted stimuli.
Suppose, say Hobson and Friston, something that you did not already realize was there appears in your peripheral vision. PGO waves are produced in the lateral geniculate body. These waves are then passed on to your occipital cortex, the part of your brain that processes visual information. Neurons in your occipital cortex then cause your eyes to move so that you can get a better look at the unexpected object.
If you experience the same stimulus over and over when you are awake (the stimulus ceases to be surprising), you are less likely to produce PGO waves
Scientists have discovered that during REM sleep, cells that are known as PGO burst cells, which are located in the region of pons known as the parabrachial nucleus, fire in clusters before every high amplitude PGO waves is emitted from a lateral geniculate nucleus and before every sideways eye movement.
Thus, PGO burst cells are associated with predictions of what you will see. PGO waves and PGO burst cells are also associated with senses other than sight, so they are associated with predictions of sensory experiences in general.
PGO burst cells fire during waking as well as during sleep, but they are 6 times more excitable during REM sleep than during wakefulness.
When you are dreaming, you spend much more time making predictions than you do when you are awake. You can make more predictions – which are used to construct your virtual dream world – when you are dreaming because you do not constantly have to revise your predictions so that they match your experiences of the external world.
During REM sleep, homeothermy- the maintenance of a constant body temperature – ceases.
In mammals, REM sleep is the only brain state in which homeothermy does not occur.
Neurons in the hypothalamus that are usually sensitive to temperature lose their temperature sensitivity during REM sleep.
We know that when rats are deprived of REM sleep, their core body temperatures are lowered.
Animals do not enter REM sleep if it is too cold, too hot or if the temperature of their environment is very unstable.
Hobson and Friston suggest that you might need to maintain a constant body temperature in order to maintain normal consciousness.
They point out that when you have a fever, it is very hard for you to concentrate. If you are extremely cold, your mind focuses on how you can warm up, and you aren’t able to concentrate on anything else.
Friston and Hobson say that the changes in brain chemistry during REM sleep that restrict external sensory input – so that you can create a simple virtual model of the world – also cause you to become insensitive to changes in temperature. During REM sleep, your brain doesn’t recognize or respond to changes in the outside world; therefore, it does not respond to changes in temperature.