Activation Synthesis Theory: Definition | StudySmarter (2023)

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: Definition | StudySmarter (1)Dreams can feel both bizarre and meaningful,

Activation Synthesis Theory – definition

The Activation Synthesis Theory argues that dreams don't have any inherent meaning, but rather they 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: Definition | StudySmarter (2)The brain is most active during REM sleep,

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: Definition | StudySmarter (3)Brain stem's activity during sleep,

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.


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