By their nature, dreams can be difficult to study, so there is still a lot to be learned about why we dream when we’re asleep. A participant in a sleep study can be monitored and assessed in a number of ways to help researchers understand what happens to the human body during a dream, but what is “seen” by the dreamer is experienced only by them. Sleep experts believe we dream three to six times each night, and we may not remember most — or any — of those dreams. Research in this field often involves aspects of self-reporting by study participants, which can prove to be problematic if the individuals have no memory of the events they’ve been tasked with evaluating.
It seems the dreams we do recall, however, can have a profound effect on us. Many people believe there is meaning to be found in dreams, and they have been a subject of deep fascination for artists, authors, and philosophers for thousands of years. The question of why we dream requires further exploration and study, but existing research in this area has examined a number of interesting theories.
What happens to the brain during a dream?
The limbic system is a collection of structures within the brain that deals with emotions. It houses the amygdala, an area of the brain which is understood to play a role in how we process fear and threatening stimuli. The limbic system is particularly active while we dream, and so are several other parts of the brain.
The content of our dreams — including the mental images we see — comes from the cerebral cortex. Also known as grey matter, the cerebral cortex is the brain’s outermost layer of nerve cell tissue. The cortex contains four lobes: the frontal lobe, the occipital lobe, the parietal lobe, and the temporal lobe. The occipital lobe is associated with visual understanding, visual data collection, world mapping, depth and distance perception, and facial recognition. Humans are highly visual creatures, and activity in the occipital lobe is believed to increase when we dream.
The frontal lobe, however, is quite inactive during dreams. This lobe is responsible for functions like problem-solving and thinking. Low activity levels in this area of the brain while we’re dreaming could explain why we may not question the irrational or absurd events that can occur in a dream until after we wake up.
When do we dream the most?
Much of our vivid dreaming occurs during rapid eye movement (REM) sleep, when brain wave activity is almost as high as it is while we’re awake. Over the night and into the morning, we cycle through periods of REM sleep. The first cycle of REM sleep begins about 90 minutes after we first drift off, and typically lasts for around 10 minutes. These stretches of REM sleep become progressively longer throughout the night, with the longest cycle taking place in the early morning hours.
We spend approximately two hours every night dreaming and dreams can happen in any stage of sleep, but the intense episodes we tend to remember are usually a product of REM sleep.
Why do we dream?
REM sleep — the period in which much of our dreams take place — is known to play a critical role in helping the brain retain and process new information. Getting a sufficient amount of REM sleep may also boost mental concentration and aid mood regulation. Experts believe that dreaming of a learning experience may consolidate memories of information associated with that experience. One study found that after reading a short story, participants who reported having dreams related to the story had better memory of the text the following morning.
Another theory posits that dreaming is a dress rehearsal of sorts for real-life situations. Many of us can bring to mind recollections of dreams or nightmares that felt real and involved people or situations we might encounter in our daily lives. Some scientists believe that dreams serve as a way for us to practise our responses to dangerous situations so that in the event of a real-life threat, the brain can react quickly and protect itself and the body from harm.
Why do we forget our dreams?
Many people find themselves unable to remember their dreams, leading them to believe that perhaps they haven’t been dreaming at all. It’s more likely that dreams are simply being forgotten, and a study from 2019 indicates this could be a deliberate action by the brain.
Research suggests that purposeful forgetting during sleep may be managed by neurons in the brain that were previously known for producing an appetite stimulating hormone. It is thought that the activation of melanin-concentrating hormone (MCH) cells that is triggered in REM sleep prevents excess information — such as the memory of a dream — from being stored in the brain’s hippocampus. This could explain why we sometimes don’t recall what we’ve been dreaming about unless we’re awoken during or immediately after a dream.
What influences dreams?
A growing body of research supports the theory that a person’s mental health may influence the frequency and content of their dreams. One study found that compared to its control group, participants with depression reported more negative emotions and moods in their dreams.
Another study explored the link between mood, mood changes, and dreams in people with bipolar disorder. Researchers discovered that neutral moods were associated with uneventful dreams, while manic states featured bizarre dream themes. Periods of mania were often preceded by dreams of death and injury, and participants recorded fewer dreams overall in the lead up to a depressive episode.
Chemical changes that occur in the brain when a person takes certain medications (including some antidepressants and beta blockers) can also cause vivid dreams or nightmares.
Studies have indicated that dreaming may help us process emotions, prepare for real-life situations, and manage memories within the brain. Research in this area is still developing and there may be other benefits, causes, and effects associated with dreaming that are yet to be uncovered by scientists.