Sleep is a naturally recurring state of the mind and the body and is a reversible state of consciousness.
There are 4 stages of sleep with each serving its own unique purpose those being NON-REM sleep (stages 1-3) and REM sleep. (NON-REM - non rapid eye movement; REM - rapid eye movement). The majority of activity from sleep spindles are during stage 2 sleep in the brain & during the last 2 hours of an 8 hour sleep. It is procedural learning that is consolidated in stage 2 sleep.
About 45-50% of the night is spent in stage 2 sleep and about 20% in stage 3 sleep (deep sleep) which occurs approximately 30 minutes after sleep onset. This stage of deep sleep is when memories & information are moved from the hypothalamus to the frontal cortex where they are reorganised. The combination of the sleep spindles and the NON-REM stage 3 transport system means we are able to keep retrieving information learnt.
Most NREM sleep takes place before midnight and includes light and deep sleep. During this time, night terrors, sleep walking, sleep talking and often take place. During the light NON-REM sleep infants and children are easily roused but during stage 3 deep sleep children are difficult to rouse. The growth hormone is released where there is cell growth and repair, and bedwetting is common. During stage 3 sleep the immune system is also boosted, tissue repair takes place and memories are moved.
"It is the passing of time with sleep that strengthens memory"
Most REM sleep is after midnight and during this time is when confusion arousals, nightmares (common in preschool children) and sensitivity to environmental disturbances, e.g noise & light can occur. This is also when dreaming sleep takes place and is good for brain growth & development, short term memory is also converted into long term memories. The younger a child is the more REM sleep they will have.
20% of sleep accounts to REM and emotional, vivid dreaming can take place where children can wake easily and will remember their dreams (nightmares & hallucinations). Each bout of REM sleep is longer as the night goes on and this sleep is involved in creating neural pathways in infants and more REM sleep takes place if having 8 hours of sleep. Each sleep cycle that happens ends with a bout of REM sleep.
"The different stages of sleep all serve a different function and people at different ages have different amounts of each sleep stage."
Studies show that fragmented sleep or reduced sleep results in impaired performance when it comes to executive functioning which is a set of cognitive processes that are necessary for cognitive control such as attention control, cognitive inhibition, working memory and cognitive flexibility.
Sleep contributes to infant learning by facilitating neural maturation, preparing infants to process & explore and by playing a role in memory consolidation of material presented whilst a child is awake. Sleep before & after learning is essential to the process of absorbing information. Sleep deprivation in older children shuts down the memory inbox where new files are not able to be received. A lack of sleep can also contribute to a lack of immunity whereby the immune system is decreased. Younger children who still require night feeds would not be considered sleep deprived, their sleep is simply fragmented and this will not affect their brain development in any way.
Words of affirmation: Preventing overtiredness will help your child not to skip the light stages of sleep, as brain will not prioritise the sleep that is the most important (deep sleep) which will in turn ensure the sleep cycle is not shortened.