Activation Synthesis Theory

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Sleep discussions generally focus on why we sleep, what happens if we don't get enough sleep, sleep disorders, and even the stages of sleep. But, have you ever wondered why we dream and what any of those dreams we have mean? This is where the Activation Synthesis theory comes in.

The Activation Synthesis theory is the activation of specific brain regions, and its synthesis is what causes dreams. There are bursts of neural activity that stem from the brain cell through the cerebral cortex that, causes the frontal lobe to interpret those signals and give them meaning.

Generally, it is well-known that dreaming comes in the stage of REM. However, are dreams actually significant? Do they have some kind of meaning to them, or is it just something that takes place in the brain and is neurologically based? This has always been something that most people have been fascinated with. Here's all you need to know about the Activation Synthesis theory.

What Is The Activation Synthesis Theory?

The Activation Synthesis theory is generally one of the simplest that most people tend to overthink, or in most cases, they find the term somewhat intimidating. However, the key is understanding what the terms activation and synthesis mean separately. Once that understanding is there, the theory basically speaks for itself.

That is not to say that the model is not complicated. Simply put, activation means that areas of the brain are being used. Then humans need to synthesize or process that information into something that makes sense to us.

The encoding and processing of data are one of sleep's goals. The information from our conscious mind is moved from temporary to permanent memory in the brain during non-REM sleep. Data transfers from the subconscious mind to the long-term memory during REM sleep. During these processes, dreams happen.

Unlike Freud's Wish-Fulfillment or the Information Processing theory, which agrees that dreams have a meaning and a purpose, the Activation Synthesis theory pretty much says the exact opposite. This theory states that dreams are absolutely meaningless.

This theory even further states that dreams are a side effect and do not have a purpose. So, if they are meaningless, then how do they occur? The Activation Synthesis theory theorizes that dreams simply start off as random electrical activation. This random electrical activation originates from the brain stem.

Brain scans have proven that a lot of activity comes from the brain stem when we are in REM while we sleep. For example, the frontal lobe does not stop working in the reticular formation, medulla, etc. The bursts of neural activity that occur when you are asleep are proof of that activity.

Why is the fact that the frontal lobe does not stop working important? This is because the frontal lobe is responsible for interpreting and also creating meanings and those different situations you dream of. Therefore, while we are in REM, the frontal lobe interprets all the bursts of neural activity that come from the brain stem. The frontal lobe is basically just carrying out its function.

Hence why theorists state that dreams are a side effect as the frontal lobe doing its job of interpreting and creating meaning is considered as a side effect of what is happening in your brain stem. Therefore, there is no meaning or any kind of symbolism attached to dreams. [1]

Why Is The Activation Synthesis Theory Well-Liked?

This theory is well-liked because it helps explain why we can have the weirdest dreams that make no sense. Therefore, if you've had dreams that you have had no way of explaining, this theory is the best in getting you to realize that your dream is just that, a dream. There is no deeper meaning or logic to that dream.

There is one other thing that this theory explains: why, every now and then, you can get random noises outside of our dreams making their way into our dream. For example, if someone is knocking on your door in real life and that noise somehow makes its way into your dream. This is how you wake up thinking about how you were dreaming about knocking, and now someone is knocking on your door.

This is simply because the senses don't stop working when you fall asleep. This is easily proven by how you can feel when someone touches your arm while sleeping. The information from outside of your dream is still making its way to your brain, and the frontal lobe will still interpret that sound and whatever else you were dreaming about.  

Therefore, the brain stem activity is the activation part, and the cerebral cortex tries to make sense of what is happening in the synthesis part. [1]

What Is The History Of The Activation Synthesis Theory?

As with almost anything, there is a history to how certain terms came about. The Activation Synthesis theory is no exception. Two individuals in the Department of Psychiatry at Harvard Med School, namely Hobson and McCarley, described the Activation Synthesis model in the 1970s.

This is a model of dreaming, which happens to be an extension of the REMs cycling model. Before this, there are records of Babylonians that go as far back as 5000 years ago, clearly keeping track of dreams and recording them on clay pots. Not only that but also trying to interpret them.

That is still the case in this day and age. There is a list compiled numbering what a dream you had could potentially mean. Some people even use that very same dream list to bet in the lottery. Furthermore, Egyptians actually had a dream God statue they worshiped.

This theory has undergone many revisions over the years since it was created. The revisions happened due to the fact that as the years went by, humans started having increased knowledge of the brain, thanks to technology. The more is learned about the brain, the more theories that are physiologically and neurologically based are further developed. [1]

What Are The Weaknesses Of The Activation Synthesis Theory?

Theories can typically explain things only so far. There will always be some aspect that they cannot quite explain or prove thoroughly. This is the case with the Activation Synthesis Theory, as there are some holes in the theory that dreams have no meaning.

One such weakness is that this theory still does not explain why the frontal lobe in our brain chooses to interpret the activity stemming from the brain stem in the way that they do. I mean, why is a burst of neural activity being interpreted as a mystical creature kind of dream? How did the frontal lobe get to that?

Furthermore, we may have the very same neural activity at night. Still, each frontal lobe may choose to interpret that burst of electrical activity in different ways. This theory cannot explain why the frontal lobe may interpret the neural activity into different imagery for different people even when they have the same burst of neural activity when asleep.

Some other criticisms of this theory are that some people simply don't dream or people that dream but aren't necessarily in REMs sleep. Therefore, some argue that the Activation Synthesis Theory is far too limited as it theorizes that we can only dream in REMs sleep. Also, some feel that it is simply too neurological to truly explain what our dreams are all about.

There is evidence that animals also dream in their sleep. If you're a dog owner, I'm sure you've seen what looks like your dog running in their sleep. That's because they dream of running in their sleep. However, there is no definitive to truly say that it can be fully proven.

Some people feel that because it is mainly based on animal research, it is highly possible that it may not apply to humans as we do not function the exact same way, even though animals typically studied have a similar nervous system.

Furthermore, some FMRI evidence has suggested that the initiation of dreaming occurs in the cerebral cortex and not the brain stem. Ultimately, this dream theory, along with the other, doesn't truly explain why we dream in a way that gives it justice.  [2]

Activation Synthesis In People With Brain Stem Damage

Studies have been conducted on people who have sustained damage to their brain stems. It has been proven that their bursts of neural activity firing from the brain stem are actually not the same as what a person who hasn't sustained damage to their brain stem would be.

However, these people with damaged brain stems are still dreaming. Dreaming does not stop just because the brain stem is damaged. As dreaming still occurs when a brain stem is damaged, and neural activity is still being fired off, the Activation Synthesis Theory is still in effect. [3]

What Happens If The Frontal Lobe Is Damaged?

The brain comprises four lobes, one of them being the frontal lobe. Each lobe has a different function and also controls different behaviors. Unfortunately, the frontal lobe is one of those lobes that is more susceptible to damage as there happen to be many more bony prominences at the front of the skull.

An injury to the frontal lobe will affect the ability to multitask and judgment, but this does not affect dreaming. The science is still up in the air. Still, some evidence suggests that the hippocampus, situated deep inside the temporal lobe, plays a role in dreams.

However, it isn't clear if dreaming stops when the hippocampus is damaged. More research is still to be conducted into whether or not the anatomy linked to the Activation Synthesis Theory stops dreaming when damaged. [5]

What Happens If One Has A REMs Sleep Disorder?

When evaluating the Activation Synthesis Theory, there is one aspect that is particularly interesting as this theory is all about REMs sleep. When focusing on people who do not get the switch of commands, you realize that their brain stem is not damaged and is very active and still sending signals to the brain to alert it to the fact that that individual is in REMs sleep.

However, the muscles just don't comprehend that and, therefore, do not get that switch-off command. This is called a REMs sleep disorder. The subcoeruleus nucleus, a tiny cluster of cells located in the brain stem, regulates REM sleep. Individuals don't really undergo the muscle paralysis linked with REM sleep once those cells are damaged or ill.

This can result in REM sleep behavior disorder, a dangerous condition in which those affected violently play out their dreams. So, what happens when this is the case? Those with this disorder act out what they are dreaming as if they are awake. Take the example mentioned above of a dog acting out running in their sleep. 

Although it is usually certain animals that are more likely to do this. There are humans that have this disorder. There are humans that sleep talk, sleepwalk, sleep eat, etc., but that is not necessarily the disorder. Humans with REMs sleep disorder experience physical, violent outbursts during sleep.

Since the discovery of REMs sleep disorder, research has revealed that three degenerative brain illnesses affect the majority of these patients. The most prominent one happens to be Parkinson's disease, a motor system-affected degenerative condition that occurs in the central nervous system.

Dementia is another type of brain illness caused by REMs disorder. Symptoms include forgetfulness, erratic alertness, visual hallucinations, and difficulty walking. The other well-known condition is multiple system atrophy. This brain illness is known to affect the area of the nervous system that regulates both voluntary and involuntary motions, such as digestion. [4]


People generally have an innate hunger to figure out what dreams mean. Psychologists still aren't 100 percent sure why we dream. Still, there have been several theories that are credible and accepted, one being the Activation Synthesis theory.

Dreams are generally just our brains trying to find meaning in the random signals that the brain stem keeps firing according to the Activation Synthesis Theory. Therefore, trying to put meaning to them is pointless as it all simply has to do with the interpretation of the neural activity.


Reference this article:

Practical Psychology. (2022, August). Activation Synthesis Theory. Retrieved from

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