By Dr. Osman Shabir, Ph.D. Reviewed by Emily Henderson, B.Sc.
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.
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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.
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