Throughout the ages, dreams have had special significance for people. You may not remember most of your dreams, but everyone spends about two hours per night dreaming. The brain does not switch off when you go to sleep, but it is highly active during certain parts of the night, especially while dreaming.
Modern research methods – since the invention of noninvasive methods for imaging the brain – highlight the areas of the brain that show activity during dream cycles. As a result, many scientists, including neuroscientists, have come up with plausible theories that try to explain why we dream at night. However, the truth is that no one really knows why we dream. What scientists do know, is the functionality of the areas in the brain that are active when we dream.
Remember, the human brain is the most sophisticated, complex system in the known universe!
Stages of sleep:
Every night we go through five different stages of sleep, which forms a cycle that is repeated at intervals of about 90 minutes during the night. The five stages of sleep are characterized by four stages of non-REM (rapid eye movement) sleep and one final stage of REM sleep. Dreams mostly occur during this final stage of sleep.
The brain also has two awake states, namely relaxed awareness, and awareness with concentrated attention.
The first four stages of non-REM sleep are restorative and mostly dreamless. Electroencephalogram (EEG) recordings from the scalp show unique patterns of brain electrical activity during each of these stages.
- Stage 1: When falling asleep a person enters the first stage of sleep, which is a noticeably light sleep with muscle tone relaxing as we slumber. The brain changes its electrical oscillations into a slower rhythm, as shown on the EEG (4-7 Hz).
- Stage 2: Stage 2 is a deeper sleep and is characterized by a drop in the body’s temperature, with the heartbeat and breathing becoming slower. The brainwaves slow down further, with short bursts of electrical activity in the brain, which appear as sleep spindles on the EEG (12-14 Hz). Sleep spindles are occasional bursts of higher frequency electrical brain activity and manifests as soon as we leave the transitionary state of sleep onset and enter the light phases of non-REM sleep.
- Stage 3 and 4: These stages of deeper sleep are characterized by high-amplitude delta rhythm (0,5-4 Hz), with a pattern of rhythmic slow waves indicated on the EEG. The heart rate and breathing, as well as brain activity, slows down to their lowest point. These deep sleep stages are what our bodies need to wake up feeling restored and refreshed.
- REM stage: REM sleep is the final stage of the sleep cycle and is aptly named after the way the eyes literally moving rapidly behind closed eyelids. The rapid roving movements of the eyes are accompanied by shallow and irregular breathing, increases in heart rate and blood pressure to near waking levels, while limb muscles become temporarily paralyzed. During REM sleep, which happens four to five times per night, the brain shows waves on the EEG that are fast and small, like the waves produced when we are awake, which indicate there are active and “awake” areas in the brain. As people grow older, they experience lees and less REM sleep.
Dreaming and REM sleep are strongly associated, as areas of the visual cortex are heavily activated during REM sleep. When people are awakened during REM sleep, they often report that they were dreaming, while people awakened from the other stages of deep sleep seldom report dreams.
The way dreams are formed:
As the brain is regarded as the most complex biological structure in the known universe, the neuroscience community continuously explores the tiny universe between our ears.
The scientific discoveries and knowledge revealed by leading global non-profit neuroscientific organizations, all involved in brain research, are shared on a public information initiative, called BrainFacts.org, which also covers research into dreams.
According to BrainFacts.org, dreams are created when your brain strings together random fragments from your memories and imagination. Most dreams combine and mix fragments of the imagination and memory, all related to the dreamer’s interests and concerns. Only about 2% of dreams replay certain events in the exact same way that they have previously happened in reality. These dreams are called episodic dreams.
The cortex, responsible for higher brain functions such as learning, memory, consciousness, voluntary movement, and coordination of sensory information, is highly active during REM sleep. As the cortex sends signals to the body and our muscles cannot move due to sleep paralysis, we move in our dreams. While we are in deep REM sleep our sensory inputs (such as seeing, hearing) are weakened, and then memory fragments in the brain are used to create the images, thoughts, and narratives that we experience as dreams.
As parts of the cortex are active during dreams, neurons firing in the visual cortex create the illusion that we are seeing things, and likewise neurons firing in the auditory cortex create the illusion that we are hearing things. Therefore, dreams feel real to us. The prefrontal part of the cortex, which deals with logic and self-control, is less active during REM sleep and this could explain why dreams often seem illogical and disorganized. This may explain why we lose touch with reality and often have hallucinatory types of experiences in our dreams. The probable reason why most of our dreams are instantly forgotten when we wake up, results from the prefrontal cortex becoming active (and logical) again as soon as we wake up.
While sensory areas in the brain become active during dreaming, the areas in the brain that place objects in physical context are not activated, which may explain why the proportions of objects can be bizarrely distorted in our dreams.
“Dreams are our mind’s attempt to paint a story from the random images and fragments that are signaled to it”, according to BrainFacts.org.
Why we forget our dreams:
We often wake up with vague memories of a dream we had during the night, but the details are lost. Very few dreams are vividly remembered, as most of them are soon forgotten. Why don’t we remember our dreams, especially the touchingly beautiful ones?
Recent research has identified specific neurons in the hippocampus in the brain that may play a role, as the hippocampus is crucial for the forming of memories. Experiments have shown that some of these neurons produce a melanin-concentrating hormone (MCH) that helps to regulate sleep. When these brain cells fire up during REM sleep, the MCN plays a role in whether the brain remembers new information. As REM sleep is the stage of sleep when we dream, and the brain cells that produce MCH are also activated during REM sleep, researchers conclude that the activation of these neurons may prevent the content of dreams from being stored in the hippocampus (the center of memory in the brain) and the dream is soon forgotten.
Some theories on why we dream.
Our dreams can be interesting or even frightening at times and neuroscientists and psychologists have devoted years in trying to uncover the meaning and purpose of dreams. While scientists can determine the electrical activities taking place in the brain while we dream, the truth is that no one can say with absolute certainty why we dream.
One of the most widely accepted theories is that dreams help the brain to process memories and sort important from unimportant information.
Another theory suggests that dreams help us to make sense of emotions, as the area in the brain involved with emotions is also active during dreaming.
Well known psychoanalyst Sigmund Freud started the dream interpretation movement and believed that dreams are all about wish fulfilment and repressed thoughts or feelings manifested in an abstract way in dreams. He suggested that dreams are based on repressed desires that were either socially unacceptable or repressed for other reasons, and in his view mostly based on repressed sexual desires and symbolism.
His understudy, Carl Jung, disagreed with Freud’s views and suggested that dreams allow us to subconsciously deal with, and think through, the problems and issues of the day.
More recent theories have the advantage of modern brain imaging technology and scientific knowledge. One such theory from 2017 says dreaming is (a) like overnight therapy, as well as (b) enhancing creativity and problem-solving. Matthew Walker, professor of psychology and neuroscience at the University of California, Berkeley, explains the conclusions from his research as follows:
- (a) Dreaming is like overnight therapy: Time spent in dream sleep heals, as dreams during REM sleep appears to offer emotional resolution from difficult or even traumatic emotional episodes experienced during the day. As REM sleep is the only time the brain is devoid of the anxiety-triggering molecule noradrenaline, it implies that the emotional and memory related areas in the brain, which are activated during REM sleep, allows us to process upsetting memories in a calmer and safer brain environment – due to the drop in stress-related brain chemistry. One of the important functions of dreams seems to be the ability to help us take the sting out of painful or upsetting emotional experiences while we sleep.
- (b) Dreaming enhances creativity and problem-solving: Research has indicated that deep non-REM sleep seems to strengthen individual memories, while REM sleep seems to be the time when those memories can be combined and integrated in innovative and abstract ways. In studies where people were woken during non-REM sleep, they were not particularly creative when faced with problem solving puzzles, while people woken during REM sleep not only were more creative but were also able to solve 15-35% more puzzles than when they were awake. In another study people were shown puzzles before going to sleep and those woken during REM sleep were able to solve more puzzles then when they were awake. It seems as if their brains have put together disparate pieces of puzzles in their sleep. This ability underlies the difference between knowledge, which is the retention of individual facts, and wisdom, which refers to knowing what all these facts mean when you fit them together. Research has also found that dreaming improves creative problem solving.
- “It is said that time heals all wounds, but my research suggests that time spent in dream sleep is what heals” says Walker.
A theory formulated in the 1970’s by Harvard psychiatrists Drs. Allan Hobson and Robert McCarley suggests that dreams are made of random electrical brain impulses, as the brain tries to make sense of what it has seen and experienced during the day. During sleep the brain digs into the day’s information and starts the processing and the images in our dreams are just leftovers of brain processing and the mind trying to process what it has seen and experienced. They are of the view that there are no hidden meanings in dreams. This is borne out by research indicating that about 80% of dreams are about random events or people the dreamer does not know, and that images that appear in dreams are often unique to that dream.
A recent theory on why we dream – based on the view that dreams defend a certain area of the brain – is suggested by Dr. Dave Eagleman, a neuroscientist at Harvard Medical School. The vast and complex system of an estimated 86 billion neurons (brain cells) and their 0,2 quadrillion connections in the brain is characterized by constant rewiring and tremendous adaptability. Neurons are responsible for the rapid processing of information and the connections between neurons are constantly changing (rewiring) by finding new partners, as well as strengthening and weakening existing connections. The immense and continuous adaptability of the human brain is referred to as brain plasticity in the field of neuroscience.
Rewiring in the brain can affect certain areas, for example when somebody loses his or her eyesight, a colonization of the visual cortex by other senses can quickly occur, what he calls the rapid conquest of brain territory. He suggests that we dream at night, when the visual sense is not active due to darkness, as a defense mechanism in the brain to keep the visual cortex territory active when the visual sense is disadvantaged by darkness.
Eagleman suggest in his “defensive activation theory” that dream sleep exists to keep the neurons in the visual cortex active to combat a takeover at night by neighboring senses. During REM sleep a special set of neurons are triggered in the visual cortex to make us experience vision. People who were born blind do not experience visual images in their dreams, but have other sensory experiences, such as hearing things of feeling their way around. He subscribes this to the other senses having taken over the visual cortex area in the brain. Dream activities take place in the same area in the brain for both sighted and blind people, they differ only in the senses that are processed and experienced during dreaming.
Some reviews of Eagleman’s book “Livewired: The inside story of the ever-changing brain”, published in 2020, questions his theory. For example, Sleep Scientists Dr. Robert Stickgold, also from Harvard, asks why would our dreams also have emotional content if they simply need to provide visual images? A review by the Wall Street Journal wonders if other senses, such as smell, taste, balance, and hearing are not also under threat of cortical takeovers while we sleep.
REM sleep behaviour disorder:
An interesting but rare sleep disorder, that may more commonly occur in men 50 years or older, is a condition in which muscle movement is not fully paralyzed during REM sleep and the individuals then acting out the events taking place in their dreams.
REM sleep behaviour disorder is characterized by unusual actions or behaviour, as strange or even dangerous events take place during REM sleep. This is a type of sleep disorder known as a parasomnia.
Normally the muscle in the body goes into a state of temporary paralysis during REM sleep. However, in people with REM sleep behaviour disorder, this paralysis may be incomplete or absent, which allows the person to act out his or her dreams. They can actively move their limbs, become physically agitated, sometimes in violent ways, leave the bed, and might injure themselves or their bed partner. An aggressive or frightening dream poses a higher risk of violent movement.
Typical actions include talking, shouting, screaming, swearing, punching, kicking, lashing out, or sleepwalking. They can also clearly recall their dreams on waking, without being aware of acting out their dreams.
While the exact cause of REM sleep behaviour disorder is not clear, it has been linked to an adverse reaction to certain medication, or drug or alcohol withdrawal, or post-traumatic stress disorder, as well as to antidepressant medication in a small percentage of cases.
REM sleep behaviour disorder can be treated with medication and by making lifestyle adjustments and adapting sleep habits.
Conclusion:
Although the purpose of dreams remains a mystery, it is clear is that they play an important part in our overall mental and emotional health.
References:
Why your brain needs to dream. Published 24 October 2017. Greater Good Magazine. Greater Good Science Center. University of California. Berkeley. (www.greatergood.berkeley)
What happens in your brain while you dream? Published online and updated 26 March 2021. Sleep Matters Club. UK. (www.sleepmatters.co.uk)
What happens in the brain when we dream? Published 31 July 2019. Brain World Magazine. (www.brainworldmagazine.com)
Inside the dream mind. Published 8 May 2020. Brain World Magazine. (www.brainworldmagazine.com)
Book review: Livewired: The inside story of the ever-changing brain. Author Dr. Dave Eagleman. Review published 4 September 2020. Wall Street Journal. (www.wsj.com)
Dreams could be critical to consolidating memories, argue two sleep researchers. Published 8 February 2021. Science Magazine. (www.sciencemag.org)
How the brain paints your dreams. Published 13 September 2018. BrainFacts.org. (BrainFacts.org is a public information initiative of global nonprofit organizations that are dedicated to brain research.) (www.brainfacts.org)
Memory: How the brain constructs dreams. Published 8 June 2020. eLlife. (A science publishing organization.) (www.elife.sciences.org)
5 Theories about the dreaming brain. Published 13 March 2020. Neuroscience News and Research, Technology Networks. (www.technologynetworks.com)
How dreams defend our brains. Published 15-22 February 2021. Time Magazine. (www.time.com)
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