The answer to why we dream is something that has eluded scientists since the dawn of time. It remains one of the most mysterious functions of the human body, and even in 2020, researchers are still stumped by the question of exactly why and how we dream. But with the abundance of recent studies, we can at least start to understand what might be happening in the chemistry of dreaming.
In this post:
What chemicals are released while we dream?
Most of our dreaming happens during REM sleep, the fifth of the sleeping stages that is characterised by rapid eye movement, a highly active brain and a paradoxically paralysed body.
The brain is so active when we dream that it is virtually indistinguishable from a brain in the waking state. Even so, the chemistry of it is entirely rewired when we sleep. Many scientists attribute this to the reason dreams are so strange and bizarre.
The fact that the brain uses a lot of energy and is highly active when we sleep means that when it experiences dreaming, thousands of complex interconnections and signals are firing, activating areas of the brain that release hormones and neurotransmitters – some of which you may recognise.
Chemically an ester of acetic acid and choline, acetylcholine is one of the main neurotransmitters in the brain. Levels of this neurotransmitter are at their peak during alert wakefulness and rapid eye movement.
Among other physiological roles, scientists have repeatedly linked acetylcholine to learning and memory. Its high levels during REM sleep shows that information is being actively processed and consolidated in this stage of sleep. This is an indication that not only are dreams occurring, but also that acetylcholine plays an active and important role in dreaming.
The link between REM sleep and acetylcholine can be shown in individuals with extreme cognitive impairment, such as Alzheimer’s disease. One of the first groups of brain cells to die in patients with Alzheimer’s disease is acetylcholine, a depletion that is hallmarked by a dramatic decrease in REM sleep and dreaming as well as a loss of memory and an inability to retain information. For researchers, this strongly suggests that there is a vital link between acetylcholine and dreaming that is crucial to the brain’s ability to consolidate information.
Scientists put this theory to the test by injecting animals with a substance that behaved like acetylcholine. This was injected into the nerve cells found in the area of the brain where REM sleep originates – a part of the brainstem known as the pons. Depending on the animal, REM sleep occurred within 3 – 30 minutes and lasted anywhere between 6 minutes and 4 hours.
A similar experiment was done with rats where they were injected with an acetylcholine blocker. This suppressed the release of the neurotransmitter and in all studies, each rat experienced a rapid decline in REM sleep. These studies showed how the neurotransmitter acetylcholine impacts REM sleep and, by association, may have the potential to cause or impact dreaming.
Also known as the sleep hormone or hormone of the night, melatonin is released by the pineal gland to promote sleep. A derivative of serotonin, melatonin plays several important functions in the synchronisation of the circadian rhythm:
- It regulates blood pressure
- It regulates seasonal reproduction, such as in spring fever
- It regulates day/night cycles of sleep and wakefulness
Essentially, when it’s darker more melatonin is released by the pineal gland, making you sleepy. When it gets brighter in the morning, melatonin levels deplete to encourage wakefulness. This is the biggest culprit behind the Winter Blues, when the mornings stay darker for longer and the evenings get darker earlier.
Melatonin levels in the brain are at their peak for twelve hours during the night. They are particularly high during rapid eye movement. In fact, increased levels of melatonin can prolong the amount of REM dreaming you experience and it is often used as a treatment for insomnia.
The impact that melatonin has on dreaming is further shown in the fact that higher doses of this hormone can lead to more lucid dreams and even nightmares.
This ‘love’ or ‘cuddle’ hormone takes centre stage in the role of social bonding. A neurohormone that is released during sex, oxytocin also enhances feelings of trust, empathy, dependence and many other feelings connected to maintaining social connections.
In the hypothalamus, the nuclei that monitor the activity of oxytocin are close to the regions of the brain that monitor arousal and, interestingly, the sleep/wake states of the body. This is the first example of how oxytocin may be getting activated during sleep.
Since dreams primarily revolve around an individuals’ social interactions and relationships, with people close to them as well as with total strangers they may have passed on the street, there is a strong argument that oxytocin has influence over our dreams since it is the hormone that governs these emotions.
Take sex, for example, an action that releases oxytocin, is mediated by oxytocin and an action that pops up in dreams from time to time. Given the close and specific relationship between sex and our favourite neurohormone, it makes sense to assume that oxytocin would have the capacity to mediate sex in dreams as well as in waking life.
What is REM sleep?
REM stands for rapid eye movement, and is a phase of sleep unique to mammals, such as ourselves, and birds. During REM sleep, the following happens:
- Our eyes move randomly and quickly
- We have lower muscle tone
- We breathe quickly and irregularly
- Our blood pressure increases
- We tend to dream most vividly, as our brains are almost as active during REM as they are when we’re awake
REM sleep is one of five phases we go through when we sleep. The other four phases are called NREM, or non-rapid eye movement, sleep. REM sleep typically happens within the first hour and a half of sleep, cycling through the phases throughout the night.
How does REM sleep impact dreaming?
As with everything to do with dreaming, the precise nature and function of REM sleep remain a mystery. At the same time, there is a resounding agreement among scientists that rapid eye movement is a crucial, endogenous function in the body that has been preserved throughout mammalian evolution for a very specific reason that we’re still trying to figure out.
Despite this, researchers can still provide a framework around which we can base our understanding of how REM sleep works and how it induces dreaming.
Where does REM sleep begin?
The exact cause of rapid eye movement is an elusive subject, but there is evidence that shows it originates when as-yet-undetermined chemical signals are sent from the pons to regions of the brain that govern everything from movement to consciousness.
One region the pons sends signals to while we sleep is the thalamus. This area of the brain is comprised of extensive networks and is crucial in the relay of sensory and motor signals as well as the regulation of consciousness and sleep.
The thalamus also sends signals to all other structures of the brain. When activated during REM sleep, one region of the brain thalamus relays signals to is the cerebral cortex. This is the outer layer of the brain that monitors learning, thinking and organising information.
The activation of these specific areas of the brain not only provide an explanation for why the brain is so highly active during REM sleep, it also strengthens the connection that rapid eye movement and, by extension, dreaming have with the consolidation of information.
Why are dreams visual?
The chemical signals that are released in the brain during REM sleep also answer one of the basic questions of dreaming: why are dreams visual and where do these images come from?
As we know, the thalamus is a relay centre of sensory signals. One part of the thalamus that specifically behaves as a relay centre for the visual pathway is the lateral geniculate nucleus (LGN), and the pons also sends its elusive chemical signals here when REM sleep is underway.
The LGN is the main connection between the optic nerve and the visual processing centre known as the occipital lobe. This means that the LGN is able to take visual input from the eyes and process it so that our brains can understand what we’re seeing.
By sending signals to this visual centre while we sleep, the LGN gets triggered as we enter REM sleep. This can explain why we dream and also why we always dream of something or someone we have seen before – our dreams seem to have total access to this visual bank by the pons activating the lateral geniculate nucleus.
Here at ReAgent, we’re not only expert chemical manufacturers – we’re also inquisitive scientists! Dreaming may have eluded scientists for generations, but they’re getting closer to unravelling the mystic brain chemistry that happens while we sleep.
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