SLEEP AND DREAMS – PART I
SLEEPING
According to the World Health Organization, it is recommended that we sleep eight hours per night. However, it is known that two-thirds of adults in developed countries do not achieve this amount of sleep.
This may not surprise you, but pay attention to the consequences of not sleeping. Regularly sleeping less than six hours destroys the immune system and significantly increases the risk of developing cancer. A lifestyle with insufficient sleep is one of the determining factors in whether or not someone develops Alzheimer’s disease.
Inadequate sleep, even for a short period, can alter blood sugar levels so profoundly that the individual might be considered pre-diabetic. Poor sleep increases the risk of cardiovascular diseases by raising the likelihood of coronary arteries becoming clogged and brittle.
Sleep disorders contribute to all major psychiatric conditions, such as depression, anxiety, and suicidal tendencies.
The hormones that regulate hunger and satiety are also affected by sleep. When we do not sleep, the hunger hormone becomes more concentrated, making us feel hungrier.
Sleep is one of the most mysterious and strange biological phenomena. When we sleep, we are not eating, reproducing, or defending ourselves, making us particularly vulnerable from an evolutionary standpoint. Nevertheless, it is now understood that sleep is a common phenomenon across almost all species, suggesting that it must hold significant value and bring essential benefits.
Sleep is complex, fascinating, and highly relevant to our health, as we will explore further. We sleep for a variety of functions and benefits for both our body and brain. There is no organ in the body nor a brain process that does not benefit from or is not optimized by sleep.
TWO FACTORS DETERMINE WHEN WE WANT TO SLEEP AND WHEN WE WANT TO STAY AWAKE
Circadian Rhythm
Have you ever wondered how your body knows when it’s time to sleep or wake up? Or why you experience jet lag when traveling to a different time zone?
We are all influenced by a rhythm called the circadian rhythm. It is a powerful force that coordinates our alertness and sleepiness in a rhythmic cycle of about 24 hours.
Everyone has a circadian rhythm (“circa” means “around,” and “dian” derives from “diem,” meaning “day”). This rhythm helps determine when you want to be awake and when you want to sleep. It also influences functions such as the ideal time to eat and drink, mood and emotions, body temperature, hormonal balance, metabolism, and the amount of urine produced.
Why does sunlight influence our circadian rhythm?
The suprachiasmatic nucleus (the 24-hour biological clock within our brain; “supra” means “above,” and “chiasm” means “crossing point”) is located in the optic nerves that originate from the eyes. It is positioned here to “test” the light signals each eye sends via the optic nerve to the brain’s visual processing center. This nucleus, consisting of about 20,000 neurons, uses this communication to determine whether it is day or night, leveraging this reliable light information to reset its inherent timekeeping and maintain a 24-hour cycle.
When we experience jet lag, the suprachiasmatic nucleus maintains its rhythm regardless of external changes. For instance, when traveling across multiple time zones, modern technology allows us to move quickly, but our body and brain don’t have enough time to adapt. As a result, we may feel sleepy during the day in the new location because, in our original location, it would be nighttime. Similarly, we might struggle to fall asleep at night because, in our previous location, we would still be awake.
After a few days, the body and brain adapt to the new schedule, thanks to melatonin. Melatonin, a hormone released by the pineal gland, signals the body to start resting and preparing for sleep. This hormone, instructed by the suprachiasmatic nucleus, begins releasing into the bloodstream at dusk, acting as a notification that it is time to sleep.
Melatonin production peaks around midnight and gradually decreases until the early hours of the morning. The cessation of its production signals the brain and body that sleep has ended.
It is the rhythm that governs the biological clock, functioning in a roughly 24-hour cycle. Sunlight acts as the switch for this cycle, indicating when we should rest and when we should start the day.
Adenosine
Adenosine is a chemical that accumulates in our brain throughout the day or our waking period, increasing our desire to sleep. The longer we stay awake, the more adenosine builds up, and the sleepier we become.
Adenosine has a clever dual effect: it simultaneously decreases the activity in brain areas responsible for wakefulness.
Once asleep, the brain begins eliminating accumulated adenosine through its breakdown and removal. For adults, adenosine elimination is typically complete after about 8 hours of sleep.
WHAT IS THE PURPOSE OF SLEEP?
Despite advancements in sleep science, there is still no unanimous answer to the question: “What is the purpose of sleep?” There are various theories, including one suggesting that sleep serves to conserve energy and adapt to the environment.
For the brain, sleep enhances numerous functions, including learning ability, memory reinforcement and consolidation, logical reasoning, decision-making, maintaining the integrity of the central nervous system, and restoring brain tissue.
The saying “sleep on it” is not entirely unfounded, as sleep also allows psychological health restoration by readjusting emotional brain circuits and fostering a calmer, more serene demeanor after a night’s rest.
Sleep also restores damaged cells, stimulates and strengthens the immune system to combat harmful processes, helps the body recover from daily activities, and recharges the heart and cardiovascular system for the following day.
Additionally, sleep regulates circulating insulin and glucose levels, as well as appetite and nutritional health.
We all understand the value of good sleep and have experienced feeling revitalized after a restful night. Yet, despite this awareness, many of us, caught up in the busyness of everyday life, fail to achieve quality sleep or the 7–9 hours our bodies need to perform these functions.
WHAT IS SLEEP?
Sleep (from the Latin “somnus,” meaning the same) is a state of consciousness complementary to wakefulness (or the waking state), characterized by normal, periodic rest involving the temporary suspension of perceptual-sensory activity and voluntary motor functions. Complementary means that these states alternate regularly in most individuals. Far from being a simple state, sleep is highly complex, encompassing functions that are restored and deepened during rest.
Sleep is regulated by the most primitive part of the brain, the brainstem, which has over 300 million years of evolution. This region influences and is influenced by newer parts, such as the limbic area (200 million years) and the cerebral cortex (the newest). Sleep is divided into REM sleep (Rapid Eye Movement) and NREM sleep (Non-Rapid Eye Movement, indicating no rapid eye movements in this phase).
Sleep is characterized by a specific brain wave pattern distinct from both the wakeful state and other states of consciousness. NREM sleep accounts for about 75–80% of total adult sleep time. It usually occurs in the first 90–120 minutes of sleep, starting with relatively fast waves that gradually slow down until reaching very slow waves. These NREM sleep subphases are called S1, S2, and S3.
Each sleep phase—light NREM sleep, deep NREM sleep, and REM sleep—provides distinct benefits to the brain at different times of the night, making all types of sleep essential. In humans, the sleep cycle consists of four stages lasting approximately 90 minutes (and up to 120 minutes). This cycle can repeat four or five times throughout the night.
SLEEP STAGES
NREM Light Sleep (Stage 1)
This is a very light sleep phase lasting about 10 minutes. It begins when the eyes close, and the body starts to fall asleep, but awakening is still easy, such as from a noise in the room.
- Key characteristics:
- Not realizing you’re already asleep;
- Slower breathing;
- Possible sensation of falling;
In this phase, the muscles are not fully relaxed, so the person may move in bed or open their eyes while trying to fall asleep.
NREM Light Sleep (Stage 2)
This stage is typically referred to as light sleep. The body is relaxed and sleeping, but the mind remains alert, making it easy to awaken from movements or noises.
This phase lasts about 20 minutes and is the stage where most people spend the majority of their sleep time.
NREM Deep Sleep (Stage 3)
This is the deep sleep phase where muscles completely relax, and the body becomes less sensitive to external stimuli like noise or movement. The mind is disconnected, with dreams being rare. This stage is crucial for physical recovery, as the body repairs minor damage from daily activities.
REM Sleep (Stage 4)
REM sleep is the final stage of the sleep cycle, initially lasting about 10 minutes and beginning approximately 90 minutes after falling asleep. During this phase, the eyes move rapidly, and heart rate increases. Dreams commonly occur in this stage.
This stage is also when sleep disorders such as sleepwalking can occur, where individuals may walk around the house without waking. REM stages grow longer with each sleep cycle, lasting up to 20–30 minutes in later cycles.
BRAIN WAVES DURING SLEEP
PHASE 1
Beta waves (very low amplitude, high frequency; 13 to 30 waves/second)
Person awake and active (in a state of wakefulness). These are faster waves, signaling an active cortex and an intense state of attention. Irregular (out of sync) recording.
PHASE 2
Alpha Waves (low amplitude, 8 to 13 waves/second)
Person awake and relaxed, with eyes closed. Neurons fire at different times. Regular (synchronized) registration.
PHASE 3
Theta waves (low-medium amplitude, spike-like wakes; 3 to 7 waves/second)
Sleepy or asleep person, transitional sleep. It can be observed in the hippocampus. Theta rhythm is also observed in REM sleep. Since the hippocampus is involved in memory processing, the presence of the theta rhythm during REM sleep in that region of the brain may be related to this activity.
PHASE 4
Delta waves (high amplitude, low frequency; 3 waves/second)
Person in deep sleep. The neurons, which are involved in information processing, all fire at the same time, so the activity is synchronized. The waves are big and slow.
REM PHASE
60 to 70 waves/second
Maximum retraction of the pupil and nictitating membrane accompany the protrusions of eye movements.
SLEEP THROUGHOUT LIFE
- Before birth, a human baby spends most of the time sleeping or in a state similar to REM sleep. Any arm or leg movements are likely the result of involuntary brain activity typical of REM sleep.
- During infancy, sleep is characterized as polyphasic: many short sleep periods throughout the day and night, interspersed with periods of wakefulness, unlike adult sleep, which is monophasic. In young children and babies, sleep includes a significant number of sleep phases. When we are born, the structures that generate sleep are fully developed, fortunately, but the suprachiasmatic nucleus, responsible for the 24-hour biological clock, is not yet fully formed. Only around one year of age does this structure reach maturity, and the child begins to spend more time awake during the day—though they still nap—and more time asleep at night. By the age of four, the child adopts a biphasic sleep pattern, transitioning to a monophasic pattern only by the end of childhood.
- During adolescence, the rhythm of the suprachiasmatic nucleus is progressively pushed forward—this is a change that occurs in all teenagers worldwide. This is reflected in altered sleep and wake schedules, which often cause frustration for everyone involved. Parents want teenagers to wake up at a “reasonable” hour, but in reality, they still need more sleep to complete their circadian cycle. On the other hand, when it’s time to go to bed, the teenager is still fully awake, while adults may already feel drowsy.
- Adult sleep becomes more disorganized. The idea that adults need less sleep—and even less as they age—is a myth. The need for sleep remains the same as we grow older; the difference is that we become less capable of generating sleep. From our 20s onwards, deep sleep begins to decline, while REM sleep remains largely stable until middle age. The decline in deep NREM sleep becomes noticeable in our 30s. We begin to experience fewer hours of deep sleep, and the brain waves associated with NREM sleep become shorter, weaker, and less frequent. By the time we reach our 70s, we will have lost about 80–90% of the deep sleep we enjoyed as young adolescents.
SOME SLEEP DISORDERS
Jet lag
A sleep disorder caused by changes in schedule and biological clock.
Circadian rhythm sleep disturbances occur when a person’s internal sleep and wake schedule (their “clock”) is not aligned with the Earth’s natural light (day) and dark (night) cycle. Time zone changes and shift work commonly disrupt normal sleep and wake rhythms.
Insomnia
An inability to generate adequate sleep despite having a suitable opportunity to sleep. People with insomnia cannot produce sufficient sleep quantity or quality, even when given enough time to sleep.
Excessive Daytime Sleepiness
People experience excessive sleepiness or fall asleep during the day.
Sleepwalking
Involves some form of movement, such as walking, talking, eating, or even texting while asleep.
Narcolepsy
A neurological disorder characterized by three main symptoms:
Excessive daytime sleepiness (sudden sleep attacks, equivalent to the sleep deprivation experienced after three or four days without sleep).
Sleep paralysis (a frightening temporary inability to move or speak upon waking).
Cataplexy (a sudden loss of muscle control, which may cause head-dropping or even full-body collapse).
Restless Legs Syndrome (RLS)
A neurological disorder where a person experiences an unpleasant sensation in their legs before falling asleep, such as burning or pain, which is relieved by moving the legs.
Sleep Apnea
Breathing interruptions during sleep, which may result from airway obstruction or central nervous system issues. It is often associated with snoring.
Don’t miss PART II of this article where we’ll talk about dreams and give you tips for improving the quality of your sleep.
Thank you for reading to the end. If you have any comments or questions send me an email ana.cecilia.autora@gmail.com
This article was inspired by the books “Why Do We Sleep?” by Matthew Walker and “The Interpretation of Dreams” by Sigmund Freud.
