Why does our brain scare us by creating nightmares?

Drew Dawson, CQUniversity Australia

It is quite normal to be frightened by a dream. But our brains don't come up with secret plans to scare us with nightmares.

In the past, many people thought that dreams were a window to another world. People lived two inseparable lives: one in an awakened world and the other in a dream world.

They believed that the dream world contained a mixture of past and future, gods and goddesses, and that it helped people find purpose in their lives. 
These dreams often revealed new ideas, met new people, not necessarily benevolent, which is why some people found them frightening. Others saw it as a sign or prophecy of the gods.

When scientists began studying dreams about 200 years ago, they thought dreams were a special type of story that the brain told itself. They thought it was a special language in which ideas and emotions were explained using symbols and signs. In this dream state, different parts of the brain were talking to each other.

Let's say you dream that your house is damaged, the latter was supposed to represent the dreamer and the brain tries to tell you that you or your ego has been damaged. 
Dr. Sigmund Freud, considered by many to be the founder of psychoanalysis, wrote in 1900 a very famous book on dreams called The Interpretation of Dreams.
A hundred years ago, people began to explain things in greater depth through science and technology. This has made it possible to understand these processes differently. But that doesn't mean the way their ancestors explained dreams was necessarily wrong.

According to scientists, there are two main types of sleep, and dreams occur during a phase called REM sleep. It is called Rapid Eye Movement because at this time of night, people move their eyes quickly back and forth. It is during this phase of the night that we dream.

If you observe cats or dogs sleeping, you will sometimes see their eyes moving and their paws fidgeting. This indicates that they are in REM sleep and could perhaps be dreaming. But we don't really know what cats and dogs dream about, because they can't tell us.
The other major type of sleep is non-REM sleep, called deep sleep or slow-wave sleep. In this type of sleep, people sleep very soundly. But they don't seem to be dreaming at that moment.

For the past 50 years, some scientists have believed that dreaming is how the brain decides every day what to keep and what to throw away. In a way, it's like cleaning your room: your brain decides what you need to know and throws away what's not important.

Scientists believe that children have a harder time separating the waking world and the dream world and that they often confuse the two.

Filmmakers have brought this confusion to the screen time and time again over the years. Many films deal with how dreams can frighten and disturb us.

As you can see, many people wonder why dreams are scary. The truth is that we are not sure.

What we do know is that everyone dreams, and everyone thinks dreams can be weird, scary, and sometimes confusing. We could share the ability to dream with all warm-blooded animals, and so it is likely that this ability plays an important role in our health.

I guess everyone tries to make sense of their dreams, even scientists. But we are still unable to see inside another person's brain to know what they are dreaming about. And that's probably a good thing.

This article is republished from The Conversation under a Creative Commons license. Read the original article.