Aoife Hardesty investigates the science behind dreams, nightmares and sleep paralysis.


SLEEP is a strange state, beloved of students everywhere. We tend to associate it with rest and shutting down after a long day, but this is a bit misleading.

As we sleep, the neurons within our brains continue to talk to each other. Brain activity decreases in areas of the brain associated with conscious thought, but during sleep, other brain regions are just waking up.

These brain regions include the hippocampus, the area associated with memory formation and learning. The hippocampus is at the side of your head behind your ears. During the day, neurons within this area are active, taking in information and encoding memories. During sleep, these newly-formed memories can be fine-tuned to preserve necessary information and discard unimportant information (like what pyjamas your roommate was wearing when they ate their cereal that morning).

“Dreams come from within our brains; they are creations of our own minds, and scientists are still not entirely sure how they are formed”

The human brain is made of up a huge number of interconnecting neurons, which together form electrical circuits throughout the brain. In simple terms, memories are saved as new connections between neurons. During sleep, these connections can become strengthened, or weakened, they can even be removed completely. As this activity is going on, your brain is cycling through the stages of sleep. The two main categories of sleep are REM (Rapid Eye Movement) sleep and non-REM sleep.

Unravelling the mysteries that lie within the sleeping mind is not an easy task, but recent findings published in Nature, provide evidence for the brain fine-tuning neuronal connections during sleep, and recent work published earlier this year from two separate groups, both published in Science, provide strong support for the theory of “sleeping to forget”.

Luisa De Vivo and her team used a scanning electron microscope to re-create images of the spines present on neurons. These spines are the connections the neuron forms with other neurons. They observed a decrease in spine number after sleep, and this decrease was largest in weaker connections, whilst stronger connections remained unchanged.

Graham Diering and his colleagues studied the biochemistry of the connections. And found that proteins needed to maintain the connection can become desensitised or removed entirely from weak connections and they identified the gene responsible for this weakening to be Homer1a.

As a child, my father would tell me stories about the Sandman, a being who sprinkles sand in your eyes to help you sleep and bring you good dreams. I firmly believed him. I also believed in the power of a dreamcatcher above my bed to catch all bad dreams. The reality however is that dreams come from within our brains; they are creations of our own minds, and scientists are still not entirely sure how they are formed.

One theory is that your brain is fine tuning the memories made during the day. As it sorts through memories, some of them are registered by your frontal lobe; the front of the brain where conscious thought, planning and decision making happen. The memories then form together to make dreams. If you’re listening to someone speaking, you might even start registering the speech in your sleep (such as my mother listening to the radio, dreaming she’s a criminal).

Nightmares tend to occur when we’re feeling unwell, in our minds, or somewhere else in our bodies. The bad feelings are registered in our brains and come out in dreams. Unhappy brains make for unhappy dreams.

“During sleep, these newly-formed memories can be fine-tuned to preserve necessary information and discard unimportant information.”

Sometimes, waking from sleep goes wrong and results in a state called sleep paralysis, although it sounds cooler in other languages where it’s called things like “there’s a goblin sitting on my chest, help”. This occurs when the brain and body fall out of sync. You wake up and your brain returns to conscious state, you’re able to take in your surroundings, but your body has not responded to the waking up cues, and remains asleep. Muscles are in the semi-paralysed state in which they sleep, your chest feels tight and breathing feels difficult because your body is doing that slow, steady sleeping breathing which is unnatural during waking. Panic sets in, and this can lead to hallucinations.

Different cultures have different mythological explanations for this, often explaining the panic and pressure on one’s chest as a demon sitting on it (as you can imagine, hallucinations wouldn’t help). One such demon is the incubus or succubus, a demon which visits people in the dead of night to have sex with them, sometimes resulting in the deterioration of the person’s health or even death.

Sleep is something we all do, yet we still haven’t unravelled all its mysteries, and who knows if we ever will.