Why do we dream? How does our brain manufacture dreams? How do they relate to our consciousness? These are questions that neuroscientists have been trying to answer for the past few decades, in an effort to understand this alternate reality—known as our oneiric, or dream, state. Since dreams recur on a daily basis, dreams plays an essential role in our daily lives, influenced by our emotions and our personal experiences. However, it is still shocking how little we actually know about their structure and reality. Dreams tend to be known as vivid hallucinations that consist of a first-person narrative, and are generally non-static throughout most of the night. In contrast, the brain activity we experience during our sleep is changing constantly. This is due to the fact that we experience five stages of sleep, categorized into REM sleep and non-REM sleep. Neuronal activity is different in each of these stages, affecting the dimensions and perception of our dreams.
Neurological features and their correlation to consciousness
To understand dreams, in a philosophical and neural point of view, we must first deal with the concept of the “self”—the self is a process, not a thing or an entity. It is something that is subject to constant change and can be enacted in the process of awareness. Usually when a person becomes occupied in a manual task, they enact a bodily self that is created for that immediate environment. However, when we get overly absorbed in that task, we tend to start losing our self from our experience. Consider a situation in which you are working on easy math questions, after studying the unit for two weeks. Since you have so much experience and practice already, and the questions are not challenging, your mind will tend to wander or lose awareness. You will start to think about something else while simultaneously completing the math questions. In wandering off, you are losing your self from your experience.
When we fall asleep, our sense of self reduces greatly. When images float by in dreams, our awareness starts to get absorbed into them. Soon we become bounded and distinct from the outside world and begin dissolving into our dream state, breaking the border between our self and non-self. We experience the dream through the perspective of our self within it .
During the REM stage, a person’s eyes tends to move about, their heartbeat and breathing start to become irregular, and most of their voluntary muscles become paralyzed. The brain activity in this particular region of sleep is very intriguing, as the brain waves tend to be faster and increase in frequency, while also decreasing in voltage. These types of waves are known as theta waves, the very same types that occur during our wakeful conscious . More interestingly, these are the same waves that are experienced when trying to recollect episodic memories, which are recent experiences that the person has recently dealt with. This means that there is a strong correlation between dreams and memories and that the neurophysical mechanisms for memory retrieval also occur while dreaming.
Aside from the REM stage, there are four other stages of sleep, which are usually categorized into the S phase and D phase. These are the first two and the last two stages, of the non-Rem part, of the sleep cycle, respectively, and tend to take up majority of the time throughout the night.The S-phase of sleep is simply known for being recuperation from the day’s activities. Dreaming does not usually occur in this state, but is not unordinary. The D-phase of sleep is where dreams are usually made and where the procss of dreaming starts . These two stages tend to have dreams that are more static, shorter, less viid, and more thought-like as compared to the REM stage. This stage usually does not contain a first-person narrative or involve the concept of self. In other words, in this phase, there is connection to the outside world and no access to the dream state .
During REM sleep, our dreams tend to be different than in the other stages. They become more vivid and intense and start to resemble experiences that are being dealt with in the real world. These are the dreams that contain the perspective and the first-person awareness of our bodily self. In this stage, we are usually distant from reality and tend to enter into a new dimensional world. This phase has been linked to parts of the amygdala and hippocampus within the limbic system in our brains. These structures in the brain, which relate to the processing and memory of emotional reactions and consolidation of short term memory into long term memory, respectively, can explain why the REM stage of sleep tends to contain sensorimotor images (images having both motor and sensory components) of our subconscious feelings and emotions that are being kept deep inside of us .
The REM stage of sleep tends to rely on the pons in our brainstem. When this part of stem is critically damaged or completely destroyed, people generally stop experiencing REM sleep—however, they don’t stop dreaming. This is because the more critical regions for dreaming are actually at the temporoparietal-occipital junction in the cerebral cortex, at a place known as the inferior lingual gyrus. Destruction to even small areas of this region can affect the colour, specific dreaming dimensions, and even movement of our dreams .
When a person is awake, the primary visual cortex plays a role in consciously decoding visual signals. However, when a person is in REM sleep, this region of the brain experiences very little activity. This is because it is actually the extrastriate visual areas that are capable of decoding the highly complex visual scenes that are seen during REM sleep. This explains why the dreams that we see are more complex and different than what we see during reality .
It has also been observed that the prefrontal cortex, which is associated with thought and judgement when we are awake, exhibits very little activity during sleep, particularly REM sleep. This explains why our dreams tend to be bizarre, illogical, and socially inappropriate.
Lastly, the anterior cingulate gyrus tends to be more active during REM sleep as well. This brain structure deals with attention and motivation. It allows us to see objects more clearly and detailed, as well as carry out change whenever we get motivated to do an activity. It is due to this area of the brain that our dreams appear so vivid and changeable.
Molecules behind our dreams:
Adenosine is the molecule that regulates between sleep and wakefulness. When a person is awake, their concentration of adenosine is much higher than what it is when they are sleeping. This concentration is continuously increasing while the person is awake, until the trigger for non-REM sleep arrives. This comes by when ATP reserves, which produce adenosine by its degradation with the adenosine deaminase enzyme, are depleted once stored as glycogen in the brain. The amount of adenosine produced in the brain is reflected by the activity level of the neurons and the glial cells. Since there is intense brain activity during times of wakefulness, there is a corresponding high level of activity of the neurons and glial cells and hence a high concentration of adenosine. However, since there is a high accumulation of adenosine in the brain, there is also a corresponding depletion of ATP reserves. This causes the brain to enter into non-REM sleep in order to recover and rebuild its stores of glycogen .
The mechanisms by which adenosine acts within the brain to initiate these stages of sleep and wakefulness is done by binding to two receptors: the A1 receptor and the A2A receptor. The adenosine binds to the inhibitory A1 receptor in the basal telencephalon, thereby inhibiting the activity of the adenylate cyclase enzyme and suppressing the inflow of calcium ions into the presynaptic terminals. This causes fewer neurotransmitters, which are associated with wakefulness, to be secreted by these neurons. This inhibits wakefulness. A different process is simultaneously used to promote sleep, in which adenosine binds to the A2A receptor in the preoptic anterior hypothalamus, which has excitatory effects towards tiredness .
One of the nuclei that are essential for REM sleep is the nucleus reticularis pontis oralis (RPO), which extends from the caudal midbrain to the rostral pons. This area tends to be very active during REM sleep, because of an increase in acetylcholine levels. Acetylcholine increases the activity of these neurons and simultaneously causes a reduction in the activity of two other nuclei that produce other wakeful neurotransmitters: the dorsal raphe nucleus and the locus coeruleus, both of which are located in the rostral portion of the pons . REM sleep cannot begin unless the activities of these two nuclei are shut down, which is why they are known as “REM off” neurons. It has been theorized that the shutdown of these two neurons might help to suppress consciousness during sleep, potentially explaining why we separate from our self and the outside world during this stage of sleep.
The frontal cortex can be necessary for dreaming as well, although some parts tend to be inactivated. This is because dopamine is projected into the frontal cortex by a neural pathway that allows for these dreams to occur. It has been correlated that with more dopamine, the intensity of dreams increases.
What do our dreams mean?
The content of our dreams changes as we approach new stages of dreaming throughout the night. This is affected mainly by environmental factors that we experience in reality. Any problems or joys relevant prior to falling asleep can show up in a dream in a variety of ways. A person will often dream about someone they are romantically interested in. Watching an emotional movie will often evoke strong emotions. These changes produce very emotional dreams, where level of emotion is directly correlated to the length of the dream experienced by the user.
Gender, age and personality also play a role in shaping the content of a dream. People who are young tend to have more emotional dreams, particularly with nightmarish themes, while people who are older tend to have dreams surrounding the theme of death. Males seem to have more sexually aggressive content in their dreams, compared to females, who tend to have dreams that are more so about home and family. People who are psychotic, depressed, or have occupations in the creative arts tend to have more nightmares. Those with depression, in particular, tend to dream more of the past rather than the present. Pregnant women tend to dream about their own mothers and babies .
When we are asleep, early on in the night, we tend to dream about our distant past, but as we progress into the night, our dreams start to change and we start dreaming about present topics. Usually these topics are wishes, thoughts, and feelings that are pushed down into the subconscious, without being addressed in our waking reality. Within our dreams, this subconscious material bypasses any censorship our brains have made. The true meaning of the dream, or the latent content, is presented in a disguised form as the manifest content, the actual images and symbols we see in our dreams.
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Written by Naumen Zain
Mentored by Angela Dong