One minute you're flying through the sky, the next, you're naked in a room full of people. Except now, your teeth have started falling out? These surreal, and often illogical, experiences are what make dreams such a mystery. From ancient spiritual interpretations to modern neuroscience, people have long wondered not just what dreams mean, but why we have them at all. Are they cryptic messages from the unconscious? Perhaps a side effect of memory processing? Or maybe they are simply the brain’s way of entertaining itself while we sleep.
Attempting to answer these questions is no easy feat. Despite being a universal human experience, dreams are inherently personal. Given no one but ourselves experiences our dreams, how can the fragmented recollections we have upon waking be objectively studied? Dream research was once steeped in spirituality and mysticism, often seen as divine messages from gods or whispered guidance from ancestors (1). Even Aristotle offered his own theory, suggesting dreams were the byproduct of internal bodily movements during sleep (1). It wasn’t until the early 20th century that dreams began to be studied through a psychological lens, most notably by Sigmund Freud, who proposed that dreams contained deeply personal and symbolic insights into the unconscious mind (2).
Modern research, however, is beginning to uncover the connection between our dreams and complex cognitive processes such as memory consolidation. Techniques employed by oneirologists — that’s the fancy word for scientists specialising in the scientific study of dreams — includes fMRI, PET scans and EEG. Such methods are used to study brain activity during sleep and dreaming, particularly during REM and non-REM sleep (3). Using these technologies in tandem with qualitative descriptions gathered from individuals’ dream reports allows us to unpack the content and function of our dreams, whilst also considering questions such as why we seem to forget most of our dreams.
What dreams are made of: influences on the content of our dreams
There’s a growing body of evidence to suggest that our dream content is influenced by the consolidation of our memories as we sleep. Sleep provides an ideal neurological state for us to organise our recent memories into more long term memories (4). The reactivation and subsequent consolidation of memories in the sleeping brain appears to contribute to the content of dreams we recall upon awakening. In one study examining this phenomena, participants played extensive amounts of Tetris prior to sleeping. In the subsequent dream report collection, over 60% of participants cited seeing Tetris images in their dreams (5). This illustrates how the boundaries between waking and dreaming cognition are more porous than they appear, with dream content itself serving as a window into the neural mechanisms of memory consolidation.
Not all dreaming can be directly tied to our most recent memories, but all dreams are built upon our prior experiences. For example, the appearance of recognisable friends or foes in our dreams in turn relies on our ability to recall their features and mannerisms (6). The bizarre patchwork of familiar situations we encounter in our dreams is also likely a reflection of the adaptive process of memory consolidation, as fragments of our memories are integrated during sleep.
The Night Shift — what is the purpose of dreams
We may be inching closer to understanding what influences the content of our dreams, but why do we dream in the first place? The Threat Simulation Theory (TST) argues that dreams act as an ancient biological defence mechanism, allowing us to simulate threatening events we may encounter in our waking life (7). TST suggests that on an evolutionary scale, being able to simulate threatening events in our sleep allows us to efficiently perceive and avoid threats whilst awake, leading to greater survival and reproductive success. It is a bit hard to imagine, however, that dreaming about being naked in public is going to be the key to our survival. This is why some scientists suggest that dreams are simply the brain’s attempt to make sense of random neural activity during REM sleep. This Activation-Synthesis Theory proposes that rather than rehearsing for real-life threats, our brains may just be firing off chaotic signals which it then tries to weave into bizarre and often disjointed stories (8). Whether dreams serve as a survival tool or are simply the byproduct of random brain activity, they offer a window into the complex workings of the sleeping mind.
Vanishing Visions and the Concept of Dream Amnesia
Have you ever woken up from such an absurd dream it seems impossible to forget, only to have forgotten the details by the end of breakfast? That’s what the experts call “dream amnesia”. It’s estimated that the average person dreams four to six times per night, yet you’d be lucky to remember even one of them by morning (6). At the molecular level, noradrenaline — a neurotransmitter associated with memory consolidation — is at its lowest concentrations while we sleep (9). This depletion could be a key factor contributing to dream amnesia, preventing the transfer of our dream experiences from short-term memory to long-term memory. Different sleep stages may also influence dream recall (6). It has been suggested that waking up during or just after REM sleep leads to more vivid dreams. In contrast, dream activity is low during non-REM sleep and hence, waking up during this sleep phase may also contribute to our poor dream recall.
Although it can be disappointing to forget these wild dream experiences, dream amnesia may also serve an adaptive purpose. The “clean slate” hypothesis argues that forgetting dreams allows us to wake with a clear mind, free of the potentially disturbing content of our dreams (10). Alternatively, by maintaining a clear distinction between our dreaming and waking experiences, we are protected from confusing our dreams with reality, preventing anxiety that may otherwise ensue (11). Perhaps this forgetfulness may not be a flaw in our memory but a feature of it, helping us to preserve our mental clarity and emotional balance as we transition from the surreal world of our dreams to the demands of our waking life.
In conclusion
We may never fully unlock the secrets of our nightly adventures, but one thing is clear: dreams are a fascinating blend of memory, biology, and mystery. Whether they're ancient survival simulations, emotional clean-ups, or just the brain’s quirky way of entertaining itself while the lights are off, dreams remind us how wonderfully weird and complex the human mind truly is. Next time you find yourself tap dancing with Beyoncé or riding a roller coaster made of spaghetti, just enjoy the ride. Your brain is simply doing what it does best — keeping things entertaining, even in your sleep.
References
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Revonsuo A. The reinterpretation of dreams: An evolutionary hypothesis of the function of dreaming. Behavioral and Brain Sciences [Internet]. 2000 Dec;23(6):877–901. Available from: https://pubmed.ncbi.nlm.nih.gov/11515147/
Hobson JA, McCarley RW. The brain as a dream state generator: an activation-synthesis hypothesis of the dream process. The American journal of psychiatry [Internet]. 1977 [cited 2019 Nov 14];134(12):1335–48. Available from: https://www.ncbi.nlm.nih.gov/pubmed/21570
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