What is proper sleep and are you getting enough?

Sleep is a very basic human need that appears to be a fundamental process.  Yet the mechanism and reason why we sleep is extensively researched and still not fully understood. 

In order to understand what constitutes quality sleep, we first have to break down the physiology of sleep. According to the medical profession, sleep can be characterised by three key features:


• it is a transient reversible state (the person can be awakened)

• it is a behavioral need (some people require more sleep than others)

• it is a perceptual disengagement from the environment (one is not aware of the surrounding)

Some believe it to be habitual, as many of us have different sleep requirements and different sleep patterns/habit or cycles. Sleep is also seen as a state of unconsciousness in which the brain is relatively more responsive to internal than external stimuli. 

The predictable cycling of sleep and the reversal of relative external unresponsiveness are features that assist in distinguishing sleep from other states of unconsciousness. The brain gradually becomes less responsive to visual, auditory, and other environmental stimuli during the transition from wake to sleep. 

 
It used to be believed that humans need to sleep for the body to get rest; however, we are currently aware that sleep is meant for the brain to get rejuvenation 
and rest. The average human spends about 6 to 8 hours per day sleeping, for some it can be up to 10 hours per day, while others can do with just four hours per day. Hence, we spend about one third of the day sleeping, and therefore, one-third of our lifetime sleeping, yet so many of us take sleep for granted.  

As we spend one-third of our life sleeping, for the average Singaporean who lives up to about 85 years old (current life expectancy), we sleep for a total of 28 years of our life!

Sleep is an Active
Process

Most of us assume that sleep is a passive event, where we close our eyes and all our bodily functions “turn/switch off”. Contrary to popular belief, sleep is an active process involving complex interactions with increased metabolic functions and activities within the brain. Metabolic brain scans have shown that during dream sleep, the brain activity is more intense and active compared to the brain in non-dream sleep and in the awake state; hence, during dream sleep the brain is so active, and yet it is important in rejuvenation, repair and memory re-building of the brain.

Dream Sleep and Non-Dream Sleep


Sleep is divided into two main phases: dream sleep (rapid eye movement or REM) and non-dream sleep (non-REM). Stage four sleep and dream sleep is also known as slow-wave/delta wave sleep (SWS), when the brain waves slow down to a very slow and coordinated pattern. 

On average, dream sleep comprises about 25% to 30% of the entire sleep in an adult. In a child however, dream sleep may be as high as 50% of the entire night’s rest. Research done on metabolic activity of the brain during different phases of sleep and wake states, demonstrated increased metabolic activity in most parts of the brain during dream sleep compared to non-dream sleep and even the wake state. Most sleep experts believe that dream sleep is crucial for 
the human.  

It is well accepted that dream sleep is the most important element in the sleep process, for well being, memory re-building, rejuvenation and mental alertness. Hence, dream sleep is vital to the human mind and body.  

Dream sleep is characterised by slow delta waves in the brain, increased metabolic activity in the brain, and rapid eye movements (REM). Rapid eye movements during dream sleep are a medical phenomenon that helps us identify dreaming events but scientist cannot explain their need. 

Simplistically, dream sleep is a highly active brain in a “paralysed” body. This is a natural reaction from our bodies in order to prevent us from acting out our dreams (i.e. if one was dreaming that one was playing soccer, one does not actually kick the bed-partner). This, however, works against the patient with a narrow airway, as the already narrowed airway will lose its tone during dream sleep and collapse, leading to upper airway obstruction, cessation of breathing and lack of oxygen. Therefore, this can lead to stress on the heart, brain and other organs in the body, a condition known as obstructive sleep apnoea (OSA).  

Obstructive sleep apnoea is the commonest sleep disorder. Due to the stoppages in breathing and low oxygen during the night, it results in interrupted sleep, sleep fragmentation and poor sleep quality. During the day, the patient is excessively sleepy, has poor concentration, poor memory and becomes irritable. Long term health consequences include high blood pressure, heart disease, strokes and sudden death 
during sleep.    

Non-Dream sleep is believed to be a complex interaction between the higher brain centers and the mid-brain. There are four stages of non-dream sleep. They progress from stage I, II, III and IV. Stage III and IV are also known as slow wave sleep (SWS).  

The exact function of this non-dream sleep (also known as non-REM sleep) is not known, although many sleep scientists postulate that during this decreased metabolic demand state in sleep, the brain can now replenish energy glucose/glycogen stores; perhaps to get ready for the next REM phase.  

Sleep Architecture

The circadian (cyclical) sleep rhythm is one of the several intrinsic body rhythms modulated by the hypothalamus (mid-brain). The sleep centre sets the body clock to approximately 24 hours, with both light and dark exposure influences the 24-hour cycle. 

The light exposure stimulates the sleep control centre directly and modulates the sleeping pattern as well (blue light stimulates the wakefulness center). A practical purpose has been proposed for the circadian rhythm, using the analogy of the brain being somewhat like a battery charging during sleep and discharging during the wake period.  

The normal human brain goes through a very systematic process every night during sleep. The brain would go through the four stages of non-dream sleep and reach dream sleep in a cyclical fashion. There are some “rules” that the brain follows:


• Sleep latency (time taken to fall asleep) varies from few minutes to half an hour.

• Dream sleep latency (time taken to have the first dream) would vary from 60 - 90 minutes.
• Amount of dream sleep varies with age (babies and children can dream 50% of the night, while adults would dream only 25 to 30% of the night)

• Most of the dream sleep is clustered in the later half of 
the night

Sleep Cycle

One sleep cycle comprises of four stages and last for about 90-120 minutes. An average sleep period a person will experience four to five complete sleep cycles. 

The sleep cycle begins systematically from stage I to IV, with four cycles of SWS (Slow-Wave Sleep). Note that after the completion of the fourth cycle, the fifth cycle does not immediately begin; instead, it is followed by a REM period. The first REM period will occur roughly 60-90 minutes after falling asleep (REM latency) and the first REM period will last only about 10-15 minutes. The length of the stages is not static, however: as the night proceeds, the length of stage three and four (also called delta or deep sleep) begins to wane, and the length of REM sleep increases.  Therefore, as the night goes on, one tends to dream for longer periods of time.

Keen to learn more about designing a bedroom that is going to help you sleep better? Read here.