Written by: Lana Adler
Updated March 12, 2021
Dreams are one of the most common human experiences. Whether we remember dreams or not, most people dream every time they sleep (1), from infancy to old age. Dreams also have the power to affect our moods (2).
But why do we dream, and what do dreams tell us about our bodies and minds? We’ll highlight the science behind dreams, including where they come from, what they might mean, and how they may benefit us.
What Are Dreams?
Dreams are stories, images, and sensations (3) created by our mind while we sleep. They often draw from our experiences, and can be extremely vivid and lifelike. At times, dreams can resemble waking life. At other times, they can be surreal.
What Is a Nightmare?
A nightmare is a vivid dream that feels upsetting. Though nightmares aren’t real, they often involve real people and situations and inspire real feelings. People have nightmares at every age, but they are reported most among children under 10 (4).
Certain factors may increase the likelihood of nightmares in some, though not all, people. Nightmares can be exacerbated or triggered (5) by:
- Frightening stimuli, such as a scary book or movie
- Stress and anxiety (6)
- Interpersonal issues and relationship tension
- Alcohol or drug use
- Certain medications, including some antidepressants, narcotics, and barbiturates
- Melatonin and other OTC sleep supplements
- Illness or fever
- Severe discomfort during sleep
- Eating just before bedtime
Though they can be quite unpleasant, nightmares are generally considered a normal part of life. In some cases, however, nightmares can occur so intensely and so often that they affect both the quality of your sleep and the quality of your waking life as a whole.
Persistent, disruptive nightmares may be a symptom of post-traumatic stress disorder (PTSD), dream disorders (7), or a number of other psychological and physiological issues. Many, if not all, of these conditions can be treated. If you feel that your nightmares are harming your quality of life, consult with your doctor about a diagnosis and treatment plan.
What Is a Night Terror?
A night terror (8) (or “sleep terror”) is a type of parasomnia, or an usual sleep behavior. During a night terror a person might sit up in bed, open their eyes, flail, scream, cry, thrash, sweat profusely, and appear to be extremely terrified.
Even though someone experiencing a night terror might look awake, night terrors actually happen during sleep or when the person has only partially awoken. While nightmares tend to happen during rapid eye movement (REM) sleep, night terrors usually happen during or between non-rapid eye movement (NREM) sleep phases. The person experiencing the night terror usually does not remember much, if any, of their experience when they wake up.
Night terrors are quite common in children, especially children between 3 and 7 years old, affecting 40% of children this age (9). Most children grow out of night terrors, often after age 10. However, night terrors can continue beyond age 10, or begin in adulthood in some rare cases.
The exact underlying cause of night terrors is unknown, though it may have something to do with a disruption in shifts between sleep phases (10). Studies have also shown that people with mental health conditions like depression, anxiety, bipolar disorder, and PTSD are more likely to experience night terrors than the average person, as are people with sleep apnea.
Like nightmares, night terrors can be jarring, but they are considered relatively normal and benign so long as they do not interfere with your daily life and sleep routine. If night terrors are interfering with your life, discuss your concerns with your doctor.
When Do We Dream?
Most dreams happen during the rapid eye movement (REM) portion of sleep. REM is the period of sleep when the brain is most active. A small portion of dreams happen outside of REM sleep (11), especially during slow-wave NREM sleep. However, the vivid dreams that we are most likely to remember upon waking usually occur during REM sleep (12).
Sleep phases come in cycles that repeat throughout the night. REM sleep occurs every 90 to 100 minutes, three to four times a night. As the night goes on, REM cycles get longer, and dreams become more vivid. Sleep scientists believe the most vivid dreams that we can remember happen during the last, longest REM cycle (13) closest to waking up.
Most dreams only last for around five to 20 minutes, though they may seem like they are going on for much longer. Short dream times allow us to have multiple dreams per night, whether or not we remember them.
Where in the Brain Do Dreams Originate?
We don’t yet have a full picture of exactly which parts of the brain are responsible for dreams. However, sleep studies have revealed a good deal about what parts of the brain seem to be involved. Areas of the brain that are active during dreaming include:
- The Brainstem: One of the most primitive parts of the brain, the brainstem helps control movement, sensation, and the involuntary nervous system. When you dream, the brainstem issues rapid-fire signals, which may be why dreams feel so tactile.
- The Amygdala: The amygdala is a tiny part of the brain that helps control emotion. Activity in the amygdala (14) may be one reason why we feel so strongly about what we experience in our dreams.
- The Hippocampus: This section of the brain has a lot to do with memory, as well as learning and emotional information. It is hyper-active during dreams. This may have to do with how vivid memories are factored into dreams, and also may indicate that dreams are involved with processing and consolidating memory (15).
- The Visual Cortex: This area in the cerebral cortex interprets and processes images and visual information. It is also highly active during dreams (16), which may be why we can see dreams play out before us.
What Happens to Our Bodies While We Dream?
There are a number of things that happen in your body during a dream, including:
- Rapid Eye Movement: Your eyes move rapidly behind your eyelids when you dream. During this time, your eyes do not send visual information to the brain (17) as they usually do during waking hours. Rather, eye motion during dreams is likely involved with visual processing during deep sleep, and possibly even the ways in which you visually experience your dream space.
- Temporary Paralysis: When you enter into REM sleep, your body is mostly immobilized. You lose almost all muscle tone, with the exception of the muscles under your eyelids and in your diaphragm. This state is called atonia and caused by a change in the neurons in the base of the brainstem (18), which are in contact with the neurons that stimulate muscle movement. Atonia may be the body trying to keep you from physically acting out your dreams in your sleep or accidentally waking yourself up.
- Twitching Muscles: While many of the muscles in your body are inactive during REM sleep because of atonia, it is common for people to involuntarily twitch, especially in the fingers and toes. While twitching was originally thought to be a part of the body’s reaction to what’s happening within a dream, it is now thought that it may have to do more with processing and mapping the neurons that connect the body to the mind (19).
- Breathing Changes: Breathing during REM sleep often becomes irregular (20), involving dramatic rising and falling. REM sleep is also characterized by brief apneas, or pauses in breathing. Apneas during REM sleep correspond to bursts of rapid eye movement and are linked to the body activating the respiratory control system during REM sleep.
- Fluctuating Heart Rate and Blood Pressure: During the NREM stages of sleep, heart rate and blood pressure usually decrease by around 20%. However, during REM sleep, heart rate and blood pressure can fluctuate wildly (21), sometimes dipping to NREM rates, and sometimes rising to an average or higher rate of breathing found in everyday life.
Why Do We Dream?
Scientists are not totally sure why we dream, but there are many interesting theories.
In the late 19th and early 20th centuries, thinkers like Sigmund Freud and Carl Jung theorized that dreams compensate for the parts of the self and the subconscious mind that do not get expressed or realized during waking life. This theory may be a helpful way for us to interpret the subject matter of our dreams culturally or psychologically. However, that model was challenged by continuity theory and supporting research (22).
Continuity theory strongly suggests that although dreams might be bizarre and strange, the person you are in your dreams is largely in line with the person you are in waking life. This theory also maintains that the reactions you have in your dream-space are largely in line with the way you react to things in real life. It is therefore considered unlikely that the only reason why we dream is to realize or express the hidden parts of the self.
Some theorists suggest that there are evolutionary reasons (23) for dreams, and that dreaming has specific biological purposes. There are several popular theories supported by recent research that discuss the purpose of dreaming.
Dreams may help you solve problems more efficiently and creatively. Sleep generally promotes creative problem-solving (24). Research suggests that dreaming in both NREM and REM sleep are very helpful in building this strength. Replaying memories in NREM dreams may be most helpful for abstracting gist information (the general rules of how things work), while replaying memories in the highly-active REM state can help you make unexpected connections and realizations. The two together may support complex problem-solving.
Cementing and Processing Memories
Dreams may help you process and store memories. Though the exact mechanisms involved are not yet fully understood, dreams may help the brain more efficiently and effectively store memories and information for later recall. Dreams may be particularly helpful in transferring memories between the hippocampus to the neocortex, which may help connect spatial and recognition memory (25).
Like other memories and important waking-life experiences, emotions may also be processed during dreams. One study showed that the same parts and processes in the brain that regulate emotion during waking hours are also involved in dreaming (26). One particular type of activity, theta activity, is especially common in emotional processing in both waking and dreaming life.
Emotional processing may also occur during nightmares. In fact, nightmares might be one of the body’s coping mechanisms. Nightmares may provide a simulation of reality in which a person has the space, distance, and relative safety to gain new emotional mastery over the traumatic events. Bizarre and surreal themes and elements in dreams may be inserted by the brain to help reduce the negative charge of the traumatic memory.
Fight or Flight Training
Dreams may come from a time when humans were constantly threatened by predators and other dangers. The purpose of dreaming, and specifically of dreaming about specific threatening events over and over again, may be to simulate those threats and play them through for practice. According to this evolutionary theory, dreams may exist because these practice methods increased survival and reproduction rates among people who had them.
Some theorists believe that we have not yet found a biological purpose for dreams, and that one may not even exist. Though human beings have certainly found many uses for dreams from a cultural perspective, it is possible that dreams may simply be an unintentional offshoot of REM sleep, and that they have no unique biological purpose in and of themselves.
Next time you wake up from a vivid dream, you may be able to better understand how it came about and what purpose it likely served.
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