Why Are Certain Dreams So Common?

January 8, 2019

The air rushes past my face, whipping my hair into my eyes as I plunge into the dark.

I blindly reach in the blackness for something, anything, to grab.

After what feels like an eternity — bam! I wake up in bed, and usually with a start.

Sound familiar? If it’s not falling, perhaps you dream of flying or being chased.

Most of us experience these so-called “typical dreams” during our lifetime.

Around three-quarters of people dream of falling, for instance, and that rate is similar across cultures.

So given the incredibly rich and complex creativity of the dreaming brain, why do some themes routinely appear?

In his 1899 book The Interpretation of Dreams, Sigmund Freud chalked falling dreams up to anxiety with — surprise, surprise — erotic undertones.

“If a woman dreams of falling, it almost invariably has a sexual sense; she is imagining herself as a ‘fallen woman’,” he wrote.

While your state of mind can influence whether your dream is nice or nasty, Freud’s hypotheses have, for the most part, fallen out of favour.

But delve into the inner working of the brain, and there are neuroscience explanations for typical dream themes.

The brain during typical dreams

Not all dreams are the result of subconscious urges bubbling to the surface, according to Rainer Schoenhammer, a psychologist at the Burg Giebichenstein University of Art and Design Halle in Germany.

Rapid eye movement or REM sleep is often called “paradoxical sleep”, Professor Schoenhammer said.

REM and non-REM sleep cycle

The first three stages of sleep are non-REM

Brain waves, heart rate, blood pressure and breathing become slower as you sink into deeper non-REM sleep

This all changes when you enter REM sleep, typically around 90 minutes after falling asleep

In REM sleep, brain wave activity increases to near waking levels, as do heart rate and blood pressure, and breathing becomes faster and irregular

You cycle through non-REM and REM sleep several times during the night, with increasingly longer, deeper REM periods towards the morning

Source: US National Institute of Neurological Disorders and Stroke

“Parts of your brain are more alert than when you’re awake, but at the same time, you are paralysed from the neck down — only your eyes move.”

Not all dreams happen in REM sleep; likewise, you can experience REM sleep and not dream.

But when the alert, REM-sleeping brain becomes aware of the paralysed body, typical dreams can rear their head.

A crucial part of the dreaming brain is the pons: the middle section of the brainstem tucked away under the brain.

It contains bundles of brain cells or neurons that help send you to sleep and wake you again.

Also in the pons are clusters of neurons that receive signals from the inner ear, or vestibular system, which helps our sense of balance and tells us what direction we’re facing.

“And it’s in exactly the same area, called the reticular formation, where the process of waking up … is installed in the brain,” Professor Schoenhammer said.

This means that when neurons responsible for waking you start to, well, wake up, so too do the neighbouring vestibular system cells, creating the sensation of being weightless, flying, falling — or even floating around as a disembodied head.

As the reticular system becomes more activated, so too does the feeling of flying or falling.

This is why you might dream that you’re falling ever faster — then wake up just before you hit the ground.

Dreams of being paralysed or “stuck” also arise from the brain-body disconnect. The alert brain, aware that the body can’t move, weaves that perception into a dream.

You see similar effects when the REM-sleeping brain senses that, for instance, you have a full bladder — so you dream of water — or you’re in bed, so your dreams take you on a magical bed ride into the sky.

Typical dreams also tend to feature in what are called “lucid dreams”, where the dreamer recognises they’re dreaming while they’re asleep.

“It’s the ultimate paradoxical sleep,” Professor Schoenhammer said.

“You’re so alert you can control what you do in the dream, but you’re still in REM sleep and paralysed.”

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