What Truly Happens When You Sleep?

by Dr. Kenny Pang
Dr Kenny Pang takes us through the processes that occur in our brain and body while we sleep and dream.

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

Sleep is divided into two main phases: dream sleep (rapid eye movement / REM) and non-dream sleep (non-REM). On average, dream sleep comprises about 25% to 30% of an adult’s entire sleep duration. In a child, however, dream sleep takes up as much as 50% of the entire night’s rest. 

Dream Sleep 

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. Dream sleep is vital to the human mind and body.  

Dream sleep, or REM sleep, is characterised by slow delta waves in the brain, increased metabolic activity in the brain, and rapid eye movements. Rapid eye movements during dream sleep are a medical phenomenon that helps us identify dreaming events but scientists cannot explain why they happen. 

Simply put, dream sleep is a highly active brain in a “paralysed” body. This prevents us from acting out our dreams – for example, if one was dreaming of playing soccer, one does not actually kick his bed partner. This, however, works against the person with a narrow airway, as the already narrowed airway will lose its tone during dream sleep and collapse. This leads to upper airway obstruction, stoppages in breathing, and oxygen deprivation, which can, in turn, lead to stress on the heart, brain, and other organs in the body. The condition is known as obstructive sleep apnea / apnoea (OSA).  

Non-dream Sleep

Non-dream sleep, or non-REM sleep, is believed to be a complex interaction between the higher brain centres and the mid-brain. There are four stages of non-dream sleep. They progress from stage I to II, III and IV. Stage III and IV are also known as slow-wave sleep or delta-wave sleep, when the brain waves slow down to a very slow and coordinated pattern.

The exact function of this non-REM sleep is not known, although many sleep scientists postulate that the decreased metabolic demands during this time allows the brain to replenish energy (glycogen) stores, and perhaps to get ready for the next REM phase.  

Stage I sleep – This stage is sometimes referred to as somnolence, or “drowsy sleep”. It is also associated with the onset of sleep; a person may have sudden twitches and hypnic jerks (involuntary muscular movements) just as he is drifting off to sleep.

Stage II sleep – During this stage, muscular activity as measured by electromyography (EMG, or muscle activity) lowers, and conscious awareness of the external environment disappears. This stage occupies 45% to 55% of total sleep.

Stage III sleep – This is considered part of deep or slow-wave sleep and appears to function primarily as a transition into stage IV. 

Stage IV sleep – Stages III and IV are the deepest forms of sleep; stage III is effectively a deeper version of stage IV, in which deep sleep characteristics, such as delta-waves, are more pronounced. This is the stage (along with stage III) in which night terrors, bedwetting, sleepwalking, and sleep talking may occur. Stage IV sleep is an important period of sleep where the growth hormone is released, and hence affects a child’s growth and development.

Sleep is important

In view of the extensive brain activity that occurs during sleep, there is reason to believe that sleep is crucial for our well-being. Make sure that you not only sleep enough hours every night, but also get good quality sleep

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