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Activation Synthesis Theory

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Activation Synthesis Theory

Why do we dream? Dreams can feel bizarre but also meaningful, healing or even prophetic at the same time. Many great scientific and technological inventions were inspired by dreams. Niels Bohr first saw the structure of an atom in his dream, Einstein's Theory of Relativity was inspired by a weird dream about cows, and Larry Page, who co-founded Google, was inspired to work on his invention by an anxiety dream.

However, the proponents of the Activation Synthesis Theory (Hobson and McCarely, 1977) would argue that there isn't a much deeper meaning to dreams. What we experience as dreams is just a creative interpretation of the brain's random activity during sleep.

  • First, we will discuss the activation synthesis theory in psychology, providing an activation synthesis theory definition
  • We will delve into various activation synthesis theory examples, before discussing any activation synthesis theory criticisms
  • Finally, we will cover the Freud vs activation synthesis theory thesis

Activation Synthesis Theory psychology

With the development of neuroimaging techniques for studying the brain came new attempts to explain what dreams are. In 1977, psychiatrists Hobson and McCarley proposed their hypothesis on dreaming, based on the neurobiological activity that was observed during REM sleep.

Contrary to Freud's theory (1900), which viewed dreams as the reflection of the unconscious, the Activation Synthesis Theory, although controversial, was supported by neuroimaging evidence.

Activation Synthesis Theory, girl sitting daydreaming with a book, StudySmarterDreams can feel both bizarre and meaningful, freepik.com

Activation Synthesis Theory definition

The Activation Synthesis Theory argues that dreams don't have any inherent meaning, but rather reflect the random activation of the brain stem during REM sleep. As REM sleep is characterised by greater activity than other sleep stages, which can be compared to the amount of activity during waking hours, the theory focuses only on REM sleep.

The Activation Synthesis Theory posits that dreams are the result of our mind's attempt to make sense of the random physiological brain activity that occurs during REM sleep.

During REM sleep the brain is very active. This brain activation suggests that rich sensory information is processed during this stage, while at the same time all motor and sensory information is blocked out from the brain. This is because of REM atonia (paralysis of muscles during REM sleep) and sensory blockade.

During REM sleep the thalamus activity suggests that all sensory information from the outside is blocked out, so the brain is isolated from the outside world during sleep.

The input that travels to the brain was proposed to be limited to impulses from the body - a result of physiological processes, which occur during sleep. Hobson and McCarley (1977) argued that the cerebral cortex creates elaborate dreams to make sense of activation caused by bodily processes.

Currently, we know that sensory processing does continue during sleep, however much more intense stimuli (louder noises or brighter lights) are needed to elicit arousal and wake us up.

Activation Synthesis Theory StudySmarterThe brain is most active during REM sleep, flaticon.com

There are two main components of the theory: activation and synthesis.

  • Activation - during REM sleep the brain appears to be very active even though it is cut off from motor and sensory stimuli. This activation was proposed to be caused by physiological processes, which occur during sleep and was termed random activation.

  • Synthesis - to make sense of this random activation, initiated by the brain stem, the cerebral cortex activates and compares this activity with our memories. That is how dreams arise, when we experience activation similar to a certain emotional state or activity from our past, a dream simulates it based on that memory.

Activation Synthesis Theory examples

Let's say that the brain's activity resembles the activity associated with running and fear. Our mind can create a dream in which we are being chased to make sense of this activation.

If the brain areas associated with pain become active our cortex can associate this activity with a recent painful memory of falling out with someone important to us and turn that into a dream.

Activation Synthesis Theory mechanism

REM sleep is initiated by the activity of the REM-ON area in the brain stem. The sensory input to the body becomes limited and muscles paralysed. Spontaneous activity in the brain stem occurs, possibly linked to other physiological processes which occur in the body at the time.

Activation Synthesis Theory, a circuit with a brain image, StudySmarterBrain stem's activity during sleep, flaticon.com

Other brain areas become activated, for example, the limbic system (responsible for emotional responses), the sensorimotor cortex (responsible for perception and movement) and the cerebral cortex. The cerebral cortex now compares this activity with existing memories and attempts to synthesise it.

Activation Synthesis Theory criticism

The Activation Synthesis Theory has inspired further theories of consciousness and dreaming and contributed to the field by providing an evidence-based neurobiological perspective on why we dream.

Still, it remains controversial and has been heavily criticised. Here are the main points of criticism of the theory:

  • The theory is reductionist, it reduces a complex psychological phenomenon of dreaming into the biological activity of different brain areas. Just because certain brain activity is correlated with dreaming, doesn't necessarily mean that this activity causes dreams or that no other processes are involved. Is the activation a result of dreams, or the cause of dreams?

  • Evidence for the Activation Synthesis Theory mainly comes from neuroimaging studies of animals. Limitations associated with the accuracy of neuroimaging techniques and animal research limit the validity and generalisability of the theory.

  • The theory only considers dreams to occur during REM sleep. We now know that dreaming occurs continuously throughout all stages of sleep, which the theory doesn't account for.

  • Some research suggests that, contrary to what the Activation Synthesis Theory predicts, dreams can be initiated with the activity in the cerebral context, not the brain stem.

  • The Activation Synthesis Theory can also be criticised for being descriptive rather than explanatory. It explains what might be causing dreams but doesn't explain their purpose.

Freud vs Activation Synthesis Theory thesis

Freud proposed that dreams are a reflection of our unconscious desires and conflicts. Because the unconscious content of our minds tends to be frightening and distressing, we don't usually have access to it. However, dream states allow us to access the unconscious indirectly, the latent content (the deeper meaning of dreams) is disguised in a symbolic manifest content or what we can remember from the dream.

According to Freud dreams do carry an underlying meaning and provide a unique insight into our unconscious, which he believed to control 75% of our behaviour.

In contrast, the Activation Synthesis Theory doesn't support the idea that dreams are very meaningful. It proposes dreams to be a result of random brain activation during sleep, which our mind attempts to interpret based on our memories.


Activation Synthesis Theory of Dreaming (Hobson and McCarley, 1977) - Key takeaways

  • The Activation Synthesis Theory, proposed by Hobson and McCarley (1977), posits that dreams are the result of our mind's attempt to make sense of the random brain activity that occurs during REM sleep.
  • The brain is isolated from outside sensory input during REM sleep due to the sensory blockade and REM atonia. Still, it remains very active during this stage, and this activity was termed random activation.
  • The random activation, initiated by the brain stem, is synthesised by the cerebral cortex, which results in dreams.
  • The Activation Synthesis Theory is based on animal studies and was criticised for limited validity and generalisability of evidence, being overly descriptive and reductionist.
  • The theory also assumes that brain activity during REM sleep is initiated by the brain stem, which isn't always the case. Moreover, the theory doesn't account for the occurrence of dreams during non-REM sleep.

Frequently Asked Questions about Activation Synthesis Theory

The Activation Synthesis Theory proposes an explanation for how dreams may arise based on the observed neural activity during REM sleep. Dreams are the result of the aforementioned areas of activity, the brain's attempt to assign meaning to the random firings and activations.


If impulses from muscles trigger activity in the brain stem, the cortex may make sense of this activity by creating a dream about being chased.

The main idea of the Activation Synthesis hypothesis is that dreams are a result of random patterns of brain activation and don't carry any inherent meaning.

Freud proposed that dreams are meaningful. Dreams reflect unconscious desires and conflicts disguised in symbolic dream content. In contrast, the Activation Synthesis Theory proposed that there is no underlying meaning to dreams, as they merely reflect the random brain activation, which occurs during REM sleep.

In the Activation Synthesis Theory, the random activation in the brain stem, which occurs during REM sleep is synthesised by the cortex as it attempts to make sense of this random activation.

Final Activation Synthesis Theory Quiz

Question

When do dreams occur according to the Activation Synthesis Theory?

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Answer

According to the Activation Synthesis Theory, dreams occur during REM sleep, when the brain is isolated from outside sensory information but remains active.

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Who proposed the Activation Synthesis Theory?

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The theory was proposed by Hobson and McCarley in 1977.

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What causes dreams according to the Activation Synthesis Theory?

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Answer

The Activation Synthesis Theory posits that dreams are the result of our mind's attempt to make sense of the random activation that occurs during REM sleep.

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How is the brain isolated from outside sensory information during REM sleep?

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Answer

This brain is isolated because of REM atonia (paralysis of muscles during REM sleep) and sensory blockade.  

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What is random activation?

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Activation of brain areas observed during REM sleep. Contrary to waking activity it is not caused by outside sensory stimuli.

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What is synthesized in the Activation Synthesis theory?


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In the Activation Synthesis Theory, the random activation in the brain stem is synthesised by the cerebral cortex.

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How does the cerebral cortex synthesise the random activation to create dreams?

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Answer

To create dreams the cerebral cortex compares the random activation with our memories 

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Where is random activation initiated according to the Activation Synthesis Theory?

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Answer

The brain stem

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What brain areas show activation during REM sleep?

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Answer

  • Brain stem
  • Limbic system
  • Sensorimotor cortex
  • Cerebral cortex

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Question

How does the Activation Synthesis Theory differ from Freud's theory of dreaming?


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Answer

Freud proposed that dreams are meaningful. Dreams reflect unconscious desires and conflicts disguised in symbolic dream content. 


In contrast, the Activation Synthesis Theory proposed that there is no underlying meaning to dreams, as they merely reflect the random brain activation, which occurs during REM sleep.

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What evidence did Hobson and McCarley use to support their theory?

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Answer

Hobson and McCarley supported their theory with neuroimaging studies on cats.

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How is the Activation Synthesis Theory reductionist?

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Answer

It reduces a complex psychological phenomenon of dreaming into the biological activity of different brain areas. Just because certain brain activity is correlated with dreaming, doesn't necessarily mean that this activity causes dreams or that no other processes are involved.

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Question

What was the Activation Synthesis Theory criticised for?

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Answer

The Activation Synthesis Theory was criticised for:

  • limited validity and generalisability of evidence,
  • being overly descriptive and reductionist,
  • assuming that brain activity during REM sleep is initiated by the brain stem, which isn't always the case,
  • assuming that dreams only occur during REM sleep.

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What is the cause of the random brain stem activation during sleep according to the Activation Synthesis Theory?

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Answer

Physiological processes that occur during sleep (e.g. breathing, heart rate, digestion etc.).

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What might be the reason for dreaming about being chased according to the Activation Synthesis Theory?

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Answer

We might dream about being chased when the cerebral cortex detects random activation associated with muscle movement and emotions like fear and synthesises it.

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What is REM sleep?

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Answer

REM sleep is the fourth stage of the sleep cycle. It is characterised by rapid eye movements, muscle paralysis, increased activation of the brain and the occurrence of vivid and immersive dreams.

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Why is REM sleep called paradoxical sleep?

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Because the brain's activity during this stage resembles our waking brain activity more than the activity that occurs during non-REM sleep.  

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How is the brain's activity different during REM sleep compared to non-REM sleep?

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During REM sleep the brain's electric activity is desynchronised and metabolic activity is increased. During non-REM sleep, the brain's electrical activity is synchronised and metabolic activity decreases.

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What causes dreams according to the Activation Synthesis Theory?

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Answer

Random brain activation during REM sleep.

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What were the findings of Williams and colleagues' (1992) study on dreams?

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Answer

They found that dreams tend to be more bizarre than daytime fantasies, showed greater plot discontinuities than fantasies and tended to play out in more remote places. 


These findings support the idea that dreams arise from random brain activation.

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What is REM atonia?

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Answer

Paralysis of muscles during REM sleep, which prevents us from acting out our dreams in real life.

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What sleep stages does the sleep cycle consist of?

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Stage 1 - entering sleep

Stage 2 - shallow sleep with K complexes and sleep spindles

Stage 3 - slow-wave sleep with decreased brain activity

Stage 4 - REM sleep 

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How does the duration of REM sleep change throughout the night?

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Answer

With each consecutive sleep cycle, REM sleep gets longer. In the first sleep cycle of the night, it only lasts around 10 minutes but by the 4th and 5th cycle it can last for up to 60 minutes. 

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What does a nap paradigm involve?

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Answer

The nap paradigm is an experimental paradigm used to study the functions of sleep. It involves measuring participants' performance on a task before and after taking a nap.

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What evidence supports the role of REM sleep in facilitating learning?

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  •  REM sleep has been shown to make up a higher proportion of the sleep cycle during development. 
  • Mednick et al. (2003) found that participants who experienced REM sleep after learning a non-declarative task performed better than participants who only experienced non-REM sleep.

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What do the findings of Cai and colleagues (2009) tell us about the function of sleep?

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REM sleep is important for creating new associations between ideas we were already exposed to. 

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What are the consequences of short-term REM sleep deprivation?

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Short-term REM sleep deprivation is associated with poorer mood regulation, memory consolidation and cognitive flexibility.

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What does the rebound phenomenon refer to?

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Answer

After a period of suppression, REM sleep becomes more frequent and intense during the next sleep periods, as the body attempts to make up for the lost REM sleep. 

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What do the findings of Lavie and colleagues (1984) tell us about the consequences of long-term REM sleep deprivation?

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Answer

The case study presented by Lavie and colleagues showed no negative cognitive consequences of long-term REM sleep deprivation.

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What is REM sleep behaviour disorder?

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Answer

REM sleep behaviour disorder is characterised by a lack of muscle paralysis during REM sleep.

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