Dreams are periods of mental activity that occur during sleep in which the sleeping person experiences imaginations and visions. The science behind dreams is limited, and the exact function remains unclear – but research has shed light on some of the mechanisms behind dreaming.
Image Credit: agsandrew/Shutterstock.com
A dream refers to the collection of mental activity that occurs during rapid eye movement (REM) portions of sleep in which mental imaginations, thoughts, visions, and sensations are perceived as “real”. The scientific study of dreams is called oneirology and is distinct to the interpretation of dreams e.g., psychoanalysis, which is more qualitative/subjective in nature.
Sleep and dreaming
Dreams typically occur during REM sleep – the portion of sleep that most resembles wakefulness. This does not mean that dreams do not occur in other portions of sleep such as slow-wave sleep (SWS); referred to as non-REM sleep but tend to be more mundane in comparison to the dreams that occur during REM sleep.
A key feature of REM sleep is that body goes into a form of paralysis (REM atonia) where motor neurons are not stimulated. As such, dreams are not typically acted upon by the sleeping individual.
Dreams have been shown to originate in the forebrain whereas REM sleep itself originates from the brainstem. Lesion studies have shown that lesions or damage to the forebrain results in the lack of dreams even in the presence of REM sleep. However, other lesions within the medial prefrontal cortex and anterior cingulate cortex can actually increase the frequency and vividness of dreams and may even persist in wakefulness.
During REM sleep, levels of both acetylcholine and dopamine are elevated, Acetylcholine keeps the brain in an active state (like wakefulness) and dopamine in high levels is linked with hallucinations (as is the case in schizophrenia or LSD-induced hallucinations). As with hallucinations, the individual perceives the visions to be “real” and it is thought that dopamine plays a role in this experience.
Alongside increases in acetylcholine and dopamine, the levels of serotonin, histamine, and noradrenaline (norepinephrine) decrease as these transmitters keep us “awake”. This is why REM sleep is paradoxical as the brain is “awake”, but the body is “asleep”.
Other forms of dreaming include lucid dreaming and nightmares. Lucid dreaming is a state between REM sleep and wakefulness in which you can “control” the narrative in your dreams. Nightmares are negative dreams which can be unpleasant and these may occur once in a while especially if you are stressed, have emotional problems, or using certain medications or drugs. Recurrent nightmares of the same story or experience could indicate a psychological issue that may be reflective of a life event or perhaps even a physical ailment.
Why do we dream? - Amy Adkins
Functions of dreaming
We still don’t fully know why we dream or what their main purpose is, but the fact they primarily (but not exclusively) occur during REM sleep could be important. REM sleep is thought to be important in normal body physiology as loss of REM sleep and/or deprivation is linked with a loss of quality of life – physically and mentally.
As such, dreaming could be a way for the body to allow the restoration of key neurotransmitters and bodily functions (repair mechanisms) that cannot happen when the body is awake. It may also play a key role in the consolidation of memories and knowledge/skills.
Whilst studying the functions of dreaming is difficult and sample sizes are limited, there is a lot of research and evidence about what happens if you do not dream (by purposefully waking people as soon as people were about to into REM sleep). Specific effects include lack of concentration, tension, anxiety, mood swings, and weight gain. The phrase “sleep on it” may also be true when it comes to dreams if you are posed with a problem or dilemma that needs thinking through as it allows for improved concentration and organized thinking, rather than making decisions when anxious or stressed.
Sleep deprivation is also linked to an increased risk of Alzheimer’s disease as during sleep the brain can efficiently clear away beta-amyloid via the glymphatic pathway, but impairments to sleep (even one night, especially during midlife) can lead to reduced amyloid clearance and increase the risk of Alzheimer’s disease. Whether this is linked directly to REM sleep and dreaming, or other parts of sleep is still unknown, though based on the other evidence it is highly likely that sleep is when such effects occur.
In summary, dreaming primarily occurs during REM sleep where the brain resembles “wakefulness” the most despite the body being in paralysis. REM sleep itself originates in the brainstem whereas dreaming originates in the forebrain. The exact functions of dreaming are disputed and not fully know, but studies of sleep and dream deprivation are linked with impaired thinking, anxiety, mood swings, and weight gain.
Functions of sleep may also include the consolidation of memories and new knowledge/skills. As technology and scientific advances improves, the mechanisms of dreaming and their exact function will become more apparent in the future.