Dreams are a fascinating mystery – whether it was a terrifying nightmare or a vivid fantasy, most of us can still vividly recall at least one. Songs have been composed and scientific discoveries realised during sleep.
But why do we dream? And how do these visions come alive in our brains?
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Why do we dream?
We still do not know a lot about dreams, but many have proposed theories to explain them.
Austrian scientist Sigmund Freud – who is the founder of psychoanalysis, a method of treating mental disorders – suggested that dreams had hidden meaning and came from desires that we pushed away. Meanwhile, Swiss psychiatrist Carl Jung said dreams were reflections of our mind and could reveal future life developments.
Later on, sleep scientists Allan Hobson and Robert McCarley said dreams happened as the brain tried to make sense of the random signals it received in sleep.
Other theories suggest that dreams are a rehearsal of real-life events that help us cope with stress. Research has found that as we dream, the brain finds meaningful patterns while getting rid of unhelpful “background noise”, which could help in problem-solving.
No single theory can fully explain dreams, but we do know that they are closely related to the stages of sleep.
Four stages of sleep
There are four stages of sleep: light non-rapid eye movement (REM) sleep stages 1 and 2, deep non-REM sleep, and REM sleep. We cycle through these stages several times throughout the night (see graphic).
Non-REM sleep consists of three parts: falling asleep, light sleep and deep sleep. During this time, brain waves slow down, and muscles slowly relax.
Each night, we spend about two hours dreaming, most of which happens during REM sleep. During this stage, our brain waves are active, and our eyes move rapidly.
But muscles experience temporary paralysis. This paralysis is caused by neurotransmitters – chemicals carrying messages between nerve cells – that stop us from physically acting out our dreams and potentially hurting ourselves.
But why do our dreams feel so real? When we sleep, the activity of the prefrontal cortex of our brain – which controls our rational judgment – decreases. But REM sleep increases the activity of the visual cortex, which controls what we see, and the amygdala, which controls emotion.
What happens when sleep cycle is disrupted
If we wake up during the first stage of non-REM sleep, we may be unaware we have been sleeping. But if we wake up in the middle of the non-REM deep sleep stage, we might feel confused and sleepy.
Some people experience a phenomenon called sleep paralysis if their sleep cycle is disrupted. When this happens, they feel as if they are conscious but cannot move. Other common symptoms of sleep paralysis include feeling like you cannot breathe or speak.
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Sleep paralysis happens when we regain awareness while going into or coming out of REM sleep. Even though it feels like we are awake, we cannot move because our motor neurons are temporarily inhibited. This often happens alongside the vivid dreams during REM sleep.
Scientists are still working to unravel the mystery of dreams, but until then, good night, and sweet dreams!
Young Post is pleased to partner with Hong Kong Science Museum and Hong Kong Space Museum on our STEM Lab series. Our aim is to encourage you in your pursuit of science. Every month, the two museums will answer your burning questions about the fantastic world around us, the cosmos, and beyond.
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