This document covers the main principles of sleep biology, including measurement of sleep patterns, brain mechanisms of sleep, and the different stages of sleep. Some of this information might help with tackling individual sleep problems as it may give a greater understanding of why some children have sleep difficulties.

Measurement of sleep patterns

A section of the brain known as the Cerebral Cortex, located in the forebrain), produces electrical rhythms that can be measured by a process called EEG (electroencephalogram). This electrical activity correlates with various human behaviours, including sleep (Bear et al, 2007).

This process, when used for measuring sleep patterns (it can also be used for diagnosing epilepsy), is usually carried out in sleep research laboratories, and is a fairly non-invasive and painless procedure. It is done by taping "electrodes" (wires) to the individual’s scalp along with conductive paste. Measurements between electrode pairs are taken and recorded on a chart consisting of "waves".

The different patterns of the waves on the chart indicate whether a person is sleeping or not, and what stage of sleep they are in. These stages are discussed below.

Stages of sleep

Below is a simplified chart to show the different stages of sleep at night and when they occur (for a young adult – the results for a child vary slightly).

Stage 1 – This is the first stage of sleep where the individual is easily aroused. The heart rate and breathing begin to slow.

Stage 2 – The individual is still fairly easily woken.

Stage 3 – The individual is difficult to wake up, and will be usually only be woken by a stimulus important to the individual, such as a mother waking to her baby’s cry even though she may not be woken by another noise at the same level. Heart rate and breathing rate drop further, as does blood pressure.

Stage 4 – As with stage 3, a person will wake for certain stimuli, and Heart, breathing rate and blood pressure are lower. By about 3 ½ hours sleep most individuals will have had all the deep sleep (stages 3 and 4) they need for the night.

REM (rapid eye movement) – This is the stage of sleep in which we dream, and our eyelids usually flicker (hence the term "rapid eye movement"). We usually have longer period of this in the second half of nighttime.

Division, growth and repair of cells often occurs at the same time each day, usually late evening and early hours of the morning (typically stages 3 and 4), although this occurs whether a person is asleep or not, so it would appear that the two might not be related. Our internal organs are usually repaired during the day and not at night, but often in times of rest (Sleep Research Centre, Loughborough University).

Sleep Mechanisms – How do we sleep?

Below is a flow chart that shows how daylight can help control an individual’s sleep.

This means that when the light disappears the body will often start to release melatonin again (therefore at night time).

Melatonin’s main function is to induce sleep, so when it is released in the dark (mainly at night time) we normally feel sleepier.

The SCN has another role as well as passing signals to the pineal gland. It also controls rhythms, known as Circadian Rhythms, meaning cycles that last about a day, the most obvious being sleep. In 1972 a French caver, Siffre, spent 7 months underground to see whether we would still produce the same rhythm of night and day without the presence of sunlight. He did indeed establish a pattern of a period of sleep and wake, the only difference being that he experienced a 25hr cycle rather than 24hr.

It may be possible that some blind individuals experience longer sleep/wake cycles for this reason (Malim and Birch, 1998).

If the SCN or hypothalamus is damaged then these mechanisms may not work in the same way, which can cause sleep difficulties.

There is evidence to suggest that having certain triggers every night, such as a song, book or, bath can also help induce sleep (Stores and Wiggs 2001), as well as factors such as optimum temperature, noise levels etc (see Good Sleep Hygiene for more details).

References

Bear, M., Connors, B., and Paradiso, M. (2007) Neuroscience: Exploring the Brain. Published by Lippincott Williams and Wilkins. USA.

Loughborough University, Sleep Research Centre, Retrieved 14th June 2008 (http://www.lboro.ac.uk/departments/hu/groups/sleep/)

Malim, T. and Birch, A. (1998) Introductory Psychology. Macmillan Pres Ltd. London.

Stores, G. and Wiggs, L. (2001) Sleep Disturbance in Children and Adolescents with disorders of development: its significance and Management. Published by Mac Keith Press. London.