Activation synthesis theory: your brain's role while dreaming
Clinically reviewed by Dr. Chris Mosunic, PhD, RD, CDCES, MBA
Explore the activation-synthesis theory and the role of the brain while dreaming. Plus, competing theories and the AIM model to understand the science behind sleep.
For centuries, people have wondered why we dream and what our dreams mean. Could a nightmare about being unprepared for a big test or presentation mean that we’re more stressed than we realize? Does dreaming about a promotion suggest that one is just around the corner? Is there any significance to seeing long-lost friends in our dreams?
The truth is, nobody knows for sure. However, there are several explanations for dreaming, including the activation-synthesis theory — the belief that dreams don’t mean as much as you think they do. This theory states that dreams happen because our brains are trying to make sense of random signals during rapid eye movement (REM) sleep.
What is the activation-synthesis theory of dreaming?
The activation-synthesis theory, proposed in 1977 by neuroscientists John Allan Hobson, MD, and Robert W. McCarley, MD, is the belief that dreams are the brain's way of making sense of random electrical signals created during REM sleep.
According to activation-synthesis theory, dreams don't have special meanings. Dreams are just the result of the brain trying to understand signals from different areas of the brain, like those responsible for emotions and memories. Surreal dreams may occur when various experiences from our lives are mixed together in strange ways.
What is the role of brain activity in dreaming?
REM is a stage of sleep where our eyes move quickly and our brain is active. During REM sleep, the brainstem sends random signals to the cortex — a part of the brain that’s in charge of thinking, remembering, and making sense of things. When the cortex gets these random signals, it tries to create a story out of them, and that’s what we experience as dreams.
At the same time, a decrease in serotonin during REM sleep—which is a neurotransmitter involved in regulating our moods—might be why dreams can sometimes feel very emotional.
What’s the scientific evidence?
While there’s substantial evidence supporting the activation-synthesis theory, it doesn’t explain all aspects of dream content and function.
Supporting evidence
Neuroimaging studies: Neuroimaging techniques, such as PET and fMRI, show increased activity in the brainstem and cortical regions during REM sleep, supporting the idea that dreams result from neural activation in these areas.
REM sleep deprivation studies: Research demonstrates that depriving people of REM sleep may affect their ability to dream. However, REM sleep and dreaming increase once normal sleep patterns are restored. This indicates a strong link between REM sleep and dreaming.
Lesion studies: Studies involving brain lesions in animals and humans show that damage to specific brainstem regions may impair REM sleep and dreaming, further supporting the role of the brainstem in initiating dreams.
Opposing evidence
Dream content and meaning: Critics argue that if dreams were purely random byproducts of the brain’s activity, they would be more fragmented and nonsensical than the clear narratives we sometimes experience in dreams.
Continuity hypothesis: This theory suggests dreams reflect ongoing concerns and experiences from waking life, challenging the idea that dreams are purely random.
Cognitive and developmental perspectives: Many researchers believe that dreams play a role in cognitive development and problem-solving — they aren't merely byproducts, as suggested by activation-synthesis theory.
Competing theories to activation-synthesis hypothesis
While activation-synthesis theory focuses on random brain signals during sleep, other theories suggest dreams may help us with memories, problem-solving, or handling threats. These theories offer different perspectives on the purpose and nature of dreaming, and there’s a lot of overlap. Essentially, it's possible that dreams have multiple purposes.
Psychodynamic theory
Famous psychoanalyst Sigmund Freud, MD, believed that dreams are expressions of our deepest desires, fears, and unresolved conflicts. He thought dreams might allow the unconscious mind to explore repressed thoughts and emotions in a safe, symbolic way.
Showing the unconscious mind: Dreams may reveal hidden desires and anxieties.
Symbolism: Dream elements may symbolize our unconscious thoughts and emotions.
Deeper meanings: Looking beyond the storyline of the dream to its hidden meaning may help us understand ourselves.
Information processing theory
This theory suggests dreams may be important in helping the brain sort, process, and store information gathered throughout the day.
Consolidating memories: Dreams may help transfer information from short-term to long-term memory.
Problem-solving: Dreams may allow the brain to process and reorganize information, which might help provide solutions to problems.
Cognitive cleanup: The brain may use dreaming to clear out unnecessary information and reinforce learning.
Cognitive theory
Cognitive theory is the idea that dreams might reflect our cognitive development and everyday thinking processes, helping us simulate real-life scenarios and practice problem-solving.
Helping cognitive development: Dreams may reflect our mental abilities and state.
Processing the world: Dream content might reflect our waking thoughts, concerns, and experiences.
Problem-solving: Dreams may help us work through issues and practice responses to real-life situations.
Threat simulation theory
Finnish psychologist Antti Revonsuo, PhD, proposed that dreams may have an evolutionary function, helping us practice our responses to potential dangers.
Evolutionary advantage: Dreaming about threats may help prepare us for real-life dangers.
Spotting threats: Dreams containing danger or conflict may help us develop survival skills by practicing and refining our reactions.
Continual-activation theory
Developed by Canadian researcher Jie Zhang, PhD, this theory suggests dreaming is part of the brain's ongoing process of maintaining and organizing memory. It divides memory processing into two types — declarative (conscious) and procedural (unconscious).
Memory maintenance: Dreaming may help maintain and organize both declarative and procedural memories.
Brain activation: The brain may remain active during sleep to continue processing and storing information.
Not confined to one sleep stage: Different types of memory processing may occur during different sleep stages.
What is the AIM model of dreaming?
The AIM model, created by Dr. Hobson, is an extension of the activation-synthesis theory. AIM stands for activation-input-modulation, and it looks at three key parts to give a more detailed explanation of how our brains might create dreams with different parts of the brain and various chemicals.
Activation: During REM sleep, the brain is almost as active as when we’re awake, which may start the dreaming process.
Input: This refers to where the information in our dreams comes from. Internal inputs can include memories and emotions. External inputs are things from the outside world, like sights or sounds. During REM sleep, inputs are usually internal because our brain is mostly shut off from the outside world.
Modulation: This pertains to how different chemicals in our brain—called neurotransmitters—may affect brain activity and dreams. During REM sleep, acetylcholine is high, which may help keep the brain active, and serotonin is low, which can make dreams more emotional.
Activation synthesis theory FAQs
How does the activation-synthesis theory contrast with Freud's theory of dreaming?
The activation-synthesis theory and Freud's theory of dreaming offer different perspectives on the purpose and nature of dreams.
Freud's theory: Sigmund Freud's psychodynamic theory, introduced in the late 19th and early 20th centuries, is that dreams can show our deepest desires, fears, and unresolved conflicts. According to Freud, dreams can allow repressed thoughts and wishes to surface in an symbolic or hidden form, but you need to interpret them to uncover their true meaning. Freud distinguished between the manifest content (the actual storyline of the dream) and the latent content (the hidden psychological meaning).
Activation-synthesis theory: Proposed by John Allan Hobson, MD, and Robert McCarley, MD, in 1977, the activation-synthesis theory suggests that dreams are the result of random neural activity originating in the brainstem during REM sleep. This neural activity triggers the cerebral cortex to try to make sense of these random signals, resulting in dreams. Unlike Freud's theory, the activation-synthesis theory supposes that dreams don’t have meaning. They’re merely as byproducts of brain processes.
How does the activation-synthesis theory explain recurring dreams?
According to activation-synthesis theory, recurring dreams happen because of repeated neural patterns and the brain's attempt to process unresolved issues or persistent thoughts.
Neural patterns: If certain neural pathways are frequently triggered during REM sleep, the brain may repeatedly try to synthesize these signals in similar ways, leading to recurring dream themes.
Unresolved issues: If you're dealing with persistent concerns, anxieties, or unresolved conflicts, these might influence neural activity during sleep. As a result, the brain’s attempt to process these issues may cause recurring dreams.
Memory and emotion: Recurring dreams can also be linked to the brain's ongoing efforts to process significant emotional experiences or memories.
Does the activation-synthesis theory account for the emotional content of dreams?
The activation-synthesis theory tries to explain the emotional content of dreams by considering the brain regions and neurotransmitters involved in emotional processing during REM sleep.
Limbic system activation: The limbic system—a group of brain structures involved in emotion, memory, and behavior—becomes highly active during REM sleep. Areas such as the amygdala and hippocampus help generate emotional responses, and the heightened activity of these regions during REM sleep may contribute to emotional experiences in dreams.
Neurotransmitters: During REM sleep, serotonin and norepinephrine levels can fluctuate, perhaps allowing more vivid and emotionally charged dreams. Meanwhile, dopamine levels can also fluctuate, perhaps enhancing the intensity and emotionality of dreams.
Synthesis of emotional experiences: The brain's attempt to understand random neural activity during REM sleep can bring emotional memories and experiences into your dreams, which may reflect your current emotional state, unresolved conflicts, and significant life events.
Are there practical applications of the activation-synthesis theory in therapy or dream analysis?
The activation-synthesis theory may provide insights into why dreaming occurs, but it can have practical applications in therapy and dream analysis too.
Sleep disorders: Understanding the neural basis of dreaming can help experts diagnose and treat sleep disorders such as insomnia, sleep apnea, and narcolepsy. By recognizing patterns of brain activation and neurotransmitter imbalances, therapists can develop interventions to improve sleep quality and manage related disorders.
Neurochemical interventions: Knowing how neurotransmitters influence dreaming can lead to pharmacological treatments, or medicines that may help. For instance, medications that affect serotonin and dopamine levels can sometimes be used to address sleep disturbances and enhance the quality of REM sleep.
Dream analysis in therapy: Although the activation-synthesis theory focuses on the biological basis of dreams, dreams often reflect our current concerns and emotional experiences. Therapists can use this information to address underlying emotional and psychological issues.
PTSD and trauma treatment: Understanding why we dream can help experts develop therapies to manage distressing dreams and nightmares. Techniques such as image rehearsal therapy (IRT)—which involves rewriting and rehearsing new dream scripts—can be informed by the theory’s insights on neural activation patterns.
Neuroscience research: Research into the neurobiological causes of dreaming may lead to new discoveries about the brain's functioning during sleep, with potential applications in fields like psychology, neuroscience, and medicine.
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