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What Causes Dreams?

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what causes dreamsWhy do we dream?

It’s a question we, as a human species, have asked for centuries. We’re used to the slow drift off to sleep and the occasional waking with a memory of something that didn’t actually take place.

Sometimes, these memories are vivid, can feel real, and even involve people we know. Other times, we can only recall bits and pieces. Often, they’re pretty weird, even if they feel real at the moment.

But what causes dreams?

Let’s explore the ins and outs of dreams.

What Are Dreams?

What are dreams, exactly? Why do we dream when we sleep?

Dreams are stories and images that appear in your head while you sleep. Dreams can occur during any of the sleep stages, but the most vivid dreams occur when you enter stage five of sleep, which is also known as the REM (rapid eye movement) stage. During the REM sleep stage, you experience dreams because it is the stage where your brain is the most active.

Lucid Dreams

Lucid dreams are defined as the dreams where you can tell you are dreaming. During lucid dreams, the parts of your brain that are typically dormant receive a boost of activity. Lucid dreams occur when your brain is in the in-between stage of REM sleep and waking up. When you are experiencing lucid dreams, you can often change or influence the story occurring within your dream and alter what is taking place.


Nightmares are “bad dreams” that occur as a result of stress, trauma, medications, or fear. Repetitious nightmares could be caused by your subconscious working while you sleep to alert you of something taking place in your everyday life.

What Causes Dreams?

The starting point to determining what causes dreams starts with delving into the brain activity that occurs when you sleep. The activation-synthesis theory proposes you dream when your brain tries to make sense of the activity it generates during sleep. The threat simulation theory claims dreams help you to prepare for danger as part of a biological defense mechanism. Finally, the information-processing theory links dreams to your body’s need to store your experiences into your memories.

Let’s dive into more information on each of these theories.

Activation-Synthesis Theory

In 1977, Harvard scientists Robert McCarley and J. Allan Hobson put forward the activation-synthesis theory. They proposed that dreams occur as the brain tries to make sense of neural activity that happens when you sleep.

You might go into a passive state when you sleep, but your brain is far from inactive. In fact, REM sleep activates the stem of your brain, which in turn causes activity in the hippocampus and amygdala, which are the areas that regulate your memories, emotions, and sensations.

The brain tries to make sense of this activity, which McCarley and Hobson believed causes dreams.

Mental Processing

Many of us dream about random things that range from the extremely realistic to the absurd. Sometimes, your dreams include things you were just thinking about when you went to sleep or random people you haven’t seen in years.

These concepts support the activation-synthesis theory. The hippocampus is a portion of the brain that is largely responsible for memory and learning. The amygdala is located near the hippocampus and regulates emotions.

When both are stimulated during sleep, you might experience a hodgepodge of emotions and memories while you sleep. It wouldn’t be too far-fetched to think that these emotions and memories then make their way into your dreams.

Threat Simulation Theory

This next theory, the threat simulation theory, claims that dreams occur as part of a biological defense mechanism.

Under this theory, dreams take place as a way to rehearse threats. It proposes that while you dream, you practice identifying and avoiding things that could cause you harm to prepare you for what may occur.

A group of researchers studied the sleep cycles of traumatized vs. less-traumatized children and found that children who have been through more unsafe situations had a higher frequency of dreams, supporting the idea that dreams occur to protect you from dangerous situations.

Information-Processing Theory

The information-processing theory doesn’t deal solely with dreams, but it does propose theories that could be related to the existence of dreams.

The information-processing theory focuses on how information becomes embedded in your memory and whether or not something becomes a long or short-term memory.

According to this theory, memory creation happens through a series of events. First, you perceive information via your senses. Your brain decides which of that information is important and stores it in your short-term memory. If you repeatedly experience or think through something, it becomes part of your long-term memory.

This is why repetition becomes such a crucial part of learning. The more you repeat something, the more likely you are to remember it.

What does this mean for dreaming?

The information-processing theory also proposes that the brain uses sleep as an opportunity to sort through and consolidate memories. Some researchers have put forward that dreaming may serve as either a byproduct or an active part of this process. Researchers purpose that as your brain goes through your memories, you perceive them, and they then slip into your dreams.

Memory Erasure

But what about the random or odder portions of your dreams? The ones where the family dog flies or you dream about that one kid from high school you were never close to?

The information-processing theory also proposes that your brain might erase some memories or consolidate them with others into long-term storage, which causes flashes of oddities in your dreams.

How Long Do You Dream?

You enter the REM cycle of sleep every one-and-a-half to two hours.

The first time you enter the REM sleep cycle, about 90 minutes after you first fall asleep, you may only stay in it for a few minutes. However, as you enter it repeatedly throughout the night, you may dream for longer.

If you get a full eight hours of sleep, you will have dreamt for approximately two hours.

Dreams come about as a part of brain activity when you sleep, which may involve the mental processing of your emotions, the consolidation of your memories, or warning signs to prepare you as a biological response. 

Sleep remains an important part of your life. The next time you sleep, pay attention to your dreams and see if any of the above theories could apply to your night!

  • Taylor Whitten

    Taylor has seen sleep apnea treatment first-hand and has learned the ins and outs through formal training in CPAP machines, masks, and equipment. She strives to make learning about sleep apnea and sleep apnea therapies a breeze. Interested in sharing your story or have a topic you’d like CPAP.com to investigate? Contact us!

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