Lifespan changes in the nature of sleep

This is part of the "nature of sleep" topic, concerning stages of sleep as well as lifespan changes. However, questions have never specifically asked about stages, and there is a lot more to talk about as well as a lot more AO2 for lifespan changes than there is for the sleep cycle. If people want a specific post on stages, I can do that as well, but this is all you should need as far as I know.


Black: AO1 - Description
Blue: AO2 - Evaluation - studies
Red: AO2 - Evaluation - evaluative points/IDAs

Lifespan changes in the nature of sleep

The nature of sleep varies dramatically over the course of the human lifespan, both in terms of the required duration of sleep, and the proportion of the different stages of sleep. The proportion of REM (rapid eye movement) sleep shows an overall decrease throughout the years, whilst the proportion of NREM (non-rapid eye movement) sleep increases.


Floyd et al (2007) reviewed nearly 400 sleep studies, and found that REM sleep decreases by an average of 0.6% a decade. The proportion of REM sleep starts to increase again from about age 70, though this may be due to an overall decline in sleep duration.


Neonates (newborn babies) sleep for over 16 hours a day over several sleep periods. After birth, they display "active sleep" - an immature form of REM sleep showing high brain activity, and "quiet sleep"- an immature form of slow-wave (deep) sleep. The proportion of quiet sleep increases and the proportion of active sleep decreases as they grow from newborns to infants. Newborns in REM sleep are often restless, with arms, legs and facial muscles moving almost constantly. Newborns enter REM sleep immediately, and do not develop the NREM/REM sleep sequence until 3 months of age. Over the first few months, proportion of REM sleep declines rapidly.


Eaton-Evans and Dugdale (1988) found that the number of sleep periods for a baby decreases until about 6 months of age, then increases until 9 months, before slowly decreasing again. This disruption between 6 and 9 months could possibly be a result of teething problems - the pain from teething leading to restless and disrupted sleep, with frequent periods of wake.

Baird et al (2009) found an increased risk of waking between midnight and 6 a.m. in infants between 6 and 12 months old whose mothers had experienced depressive symptoms during or immediately preceding pregnancy. Regular night waking in the first year is associated with later sleep disruption, behavioural problems and learning difficulties.

A real-world application of this research is emphasising the importance of the early establishment of regular sleep patterns in infants, as well as the importance of the mother's mental health during pregnancy. In order to reduce the risk of behavioural problems and learning difficulties later on in childhood, parents should attempt to settle their baby into a regular sleep pattern as soon as possible after the disrupted sleep between 6 to 9 months has passed. Research has also suggested that nurturing a regular sleep cycle can reduce the incidence of SIDS (sudden infant death syndrome) 

Puberty marks the onset of adolescence, where sexual and pituitary hormones are released in pulses during slow wave sleep (deep sleep.) Sleep quality and quantity do not change drastically, but external pressures and stress may lead to a less regular sleep cycle. Both sexes may begin to experience erotic dreams.


Crowley et al (2007) explained the change in the sleep patterns of adolescents as a result of changes in hormone levels, described as "delayed sleep phase syndrome" upsetting the circadian clock.

This study has a valuable real world application in education. Wolfson and Carskadon suggested that schools should begin later on in the day to accommodate for the poor concentration and attention spans of adolescents earlier in the morning. This change could have a positive effect on learning and productivity, thereby improving exam results and academic achievement.


A shallowing and shortening of sleep may occur in middle age, with increasing levels of fatigue. There is a decrease in the amount of stage 4 (deep) sleep, and it may be more difficult to stay awake. Weight issues may lead to respiratory problems such as snoring that can affect quality of sleep.


Van Cauter et al (2000) examined several sleep studies involving male participants, and found two periods of significant reduction in total amount of sleep: between 16 and 25, and between 35 and 50.


Only male participants were studies, so it is difficult to generalise to females too, and it would be beta bias to attempt this generalisation. Other sleep studies have demonstrated the importance of hormones in controlling circadian rhythms and the sleep cycle, suggesting that hormonal differences between men and women lead to different changes in sleep at different life stages. Also, environmental factors that affect the nature of sleep, such as stress, can affect men and women differently, meaning that the results cannot be generalised to both genders.

Conclusion

There is significant evidence to suggest that both the type and quantity of sleep vary tremendously over the course of the human lifespan, with neonates experiencing a different form of sleep to other age groups, and most people undergoing a steady decline in the proportion of REM sleep up until senescence.


Studies in this area use rigorous scientific methodology in their approach to studying sleep, often using electroencephalograph (EEG) machines to measure electrical activity in the brain over the course of a night's sleep. The use of sleep labs and EEGs provides a reliable and objective measurement of brain activity, but the use of them can impede on a study's validity. When participants sleep in a sleep lab, they are not exposed to external interruptions such as traffic or noisy neighbours that can reduce quality of sleep. Additionally, EEG equipment is bulky and uncomfortable to wear, which might also reduce quality. These factors mean that results gathered may not have very high external validity, and lack real-world generalisability.


Research also suffers from cultural bias, as many of the studies take place in the UK or the USA, and thus are more likely to include American and British participants. Assuming that results obtained are applicable globally is beta culturally biased, and likely to be incorrect - for example, many Mediterranean countries take "siestas" - daytime naps, helping split their sleep up into two blocks rather than one. Cultural practices such as these mean that conclusions drawn from studying American and British participants are unlikely to be cross-culturally applicable.