What Is the Activation-Synthesis Model of Dreaming?

Activation-synthesis suggest brain activity leads to dreaming
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The activation-synthesis theory is a neurobiological explanation of why we dream. The question of why people dream has perplexed philosophers and scientists for thousands of years, but it is only fairly recently in history that researchers have been able to take a closer look at exactly what happens in the body and brain during dreaming.

Harvard psychiatrists J. Allan Hobson and Robert McCarley first proposed their theory in 1977, suggesting that dreaming results from the brain's attempt to make sense of neural activity that takes place during sleep.

Even when you are sleeping, your brain is quite active. Hobson and McCarley suggested that during sleep, activity in some of the lower levels of the brain that are primarily responsible for basic biological processes are then interpreted by the parts of the brain responsible for higher-order functions such as thinking and processing information.

A Closer Look at the Activation-Synthesis Theory

The activation-synthesis model suggests that dreams are caused by the physiological processes of the brain. While people used to believe that sleeping and dreaming was a passive process, researchers now know that the brain is anything but quiet during sleep. A wide variety of neural activity takes place as we slumber. Part of this is because sleep helps the brain perform a number of activities including cleaning up the brain and consolidating memories from the previous day.

How does brain activity during sleep lead to dreaming?

According to Hobson and other researchers, circuits in the brain stem are activated during REM sleep. Once these circuits are activated, areas of the limbic system involved in emotions, sensations, and memories, including the amygdala and hippocampus, become active. The brain synthesizes and interprets this internal activity and attempts create meaning from these signals, which results in dreaming.

Hobson also suggested that there are five key characteristics of dreams. Dreams tend to contain illogical content, intense emotions, acceptance of strange content, strange sensory experiences, and difficulty remembering dream content.

To summarize, the activation synthesis theory essentially made three key assumptions:

  1. High levels of activity in the brainstem are necessary for dreaming to take place.
  2. Activation in these areas of the brain results in REM sleep and dreaming and that all dreaming takes place during REM sleep.
  3. The forebrain attempts to place meaning on the random signals created from the activation of the brainstem, resulting in coherent dreams.

So why does the brain try to make meaning from these random signals that take place during sleep? "The brain is so inexorably bent upon the quest for meaning that it attributes and even creates meaning when there is little or none in the data it is asked to process," Hobson suggested.

Reaction to the Theory

The initial publication of their research stirred up considerable controversy, particularly among Freudian analysts. Since many dream researchers and therapists invest considerable time and effort trying to understand the underlying meaning of dreams, the suggestion that dreams were simply the brain's way of making sense of activity during sleep did not sit well with many.

Does It Mean That Dreams Are Meaningless?

While the activation-synthesis model of dreaming relies on physiological processes to explain dreaming, it does not imply that dreams are meaningless.

According to Hobson, "Dreaming may be our most creative conscious state, one in which the chaotic, spontaneous recombination of cognitive elements produces novel configurations of information: new ideas. While many or even most of these ideas may be nonsensical, if even a few of its fanciful products are truly useful, our dream time will not have been wasted."

The AIM Model of Dreaming

Thanks to modern advances in brain imaging and the ability to monitor brain activity, researchers now understand more about the sleep-wake cycle, the different stages of sleep, and the different states of consciousness.

The more recent version of the activation-synthesis theory is known as the AIM model, standing for activation, input-output gating, and modulation. This newer model tries to capture what happens in the brain-mind space as consciousness changes through waking, non-REM, and REM sleep states.

A Word From Verywell

The reasons and meaning behind dreaming have fascinated philosophers and researchers for centuries. Activation-synthesis theory added an important dimension to our understanding of why we dream and stressed the important of neural activity during sleep. As new technology emerges for studying the brain and sleep processes, researchers will continue to make new advances in our understanding of why we dream, states of consciousness, and the possible meaning behind our dreams. 


Hobson, JA. REM sleep and dreaming: Towards a theory of protoconsciousness. Nature Reviews Neuroscience. 2010; 10(11): 803–13. 

Hobson, JA & McCarley, RW. The brain as a dream-state generator: An activation-synthesis hypothesis of the dream process. American Journal of Psychiatry. 1977; 134: 1335-1348.

Hobson, JA. The Dreaming Brain. New York: Basic Books; 1988.

Hobson, JA. Consciousness. New York: Scientific American Library; 1999.

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