Purpose of sleep VCE PSYCHOLOGY UNIT 4 Presented by Kristy Kendall Study design dot point: theories of the purpose and function of sleep (REM and NREM) including restoration theory and evolutionary (circadian) theory

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Why Sleep? Restorative theory = rest and recovery Evolutionary theory Sleep is a necessity, not a luxury. While sleep is essential to being healthy, alert and happy, the overriding purpose of sleep is much debated. We know we need sleep but we are still unclear about exactly why. The amount of sleep we need also varies markedly from one person to another. There are several theories of sleep function, including the evolutionary (circadian) theory of sleep and restorative (restore and recover) theories of sleep. Restorative theory = rest and recovery Evolutionary theory = survival / evolutionary trait © Freepik © Freepik

Purpose of sleep - restorative Restorative theory – sleep replenishes our bodies and allows us to recharge depleted energy resources REM replenishes the mind, NREM replenishes the body Sleep repairs and replenishes the body and prepares it for action the next day. Sleep looks after the health of the physical body. Activities that are more physically demanding should increase sleep Sleep increases alertness. Sleep keeps our minds alert and assists our psychological state. When we are not getting enough sleep, we tend to be inattentive and more easily distracted Sleep enhances mood. Many hormones and neurotransmitters influence your mood and emotions. A number of these are activated during sleep. As a consequence, not getting enough sleep can lead to negative thoughts, feelings and behaviours Sleep activates growth hormone. Growth hormone is responsible for physical growth. It has been linked with sleep, especially during the early years and adolescence, and the more you sleep (especially stages 3 and 4 NREM sleep), the more likely you are going to grow and meet your potential growth

Restorative theory Supportive evidence: Marathon runners spend more time in NREM sleep sleep activates growth and increases immunity Cognitive decline occurs with sleep deprivation The neurotransmitter adenosine .Adenosine is produced when our cells use energy – it is suspected to be a cellular waste product that accumulates when we are awake. The more energy we spend, the more adenosine is produced. Adenosine is linked to making us feel sleepy and the longer we are awake, the sleepier we get. When asleep, adenosine levels decrease and we wake feeling refreshed and alert Criticisms: - The assumption that more sleep is needed to recover when we are physically active. Unless we partake in extreme physical activities (such as a 100 kilometre marathon), there is little evidence that we need more sleep when we exercise. - If this assumption is true, we might expect that those who do little exercise, including people who are disabled or confined to bed, would sleep less, but there is no evidence to support this statement: bedridden people show sleep patterns that are similar to those of normally active individuals. The need for sleep is not reduced with lack of exercise. Jessica Trengrove at the 2012 London Olympics in the marathon. Source: Wikipedia

Evolutionary theory According to the evolutionary (circadian) theory of sleep, sleep is a means of increasing an animal’s chances of survival in its environment. Sleep patterns have adapted in terms of whether the animal in question is predator or prey, their food requirements and methods of defence from attack sleep is an evolutionary response that adapts based on the demands of how much we food we need, our energy requirements and our safety when we sleep. Animals such as cows graze, they therefore get little sleep because they need more time to find and consume food. Animals vulnerable to predators sleep more because they are inactive and therefore hide safely. Image used under license from Shutterstock.com

Sleep depends on an animal’s vulnerability to predators Small animals that are very vulnerable to predators, such as mice, sleep more so that they can hide safely from carnivores that will eat them. Larger prey animals, such as deer, sleep less because they are more exposed in their environment and need to be ready to escape from predators. Those with few natural predators, such as bears and lions, often sleep for long periods (12 to 15 hours) each day Sleep depends on the need to find food Animals that need to graze for hours, such as cows, sleep less. They sleep less because they need to find more food to survive. Sleep conserves energy. When an animal sleeps, its metabolism slows, thus reducing the need for food – a human’s metabolic rate during sleep is about 10 per cent less than when awake. Sleeping is a meansof conserving energy in hibernating animals

Sleep totals

Purpose of sleep - Survival Supportive evidence: there is a sequential pattern that demonstrates that the energy requirements of animals and number of predators correlates with sleep requirements sleep conserves energy, so hibernation is important when food is scarce in the Winter months. Criticisms: this theory does not explain why we must have sleep. All species sleep, despite the amount of food (abundant or scarce) or danger they are in a way to hide safely from predators. For animals that are highly preyed upon, sleeping can be dangerous. The loss of awareness during sleep makes the animal very vulnerable to predators and unlikely to be able to respond to danger. Source: Pixabay

Why do we sleep? Sleep theories are only theories but both have substantial evidence to answer this question. Restorative theory Evolutionary theory Source: Pixabay

Multiple choice activity It is generally accepted that sleep A. detoxifies the substances built up in the body during the day. B. allows time for damaged brain cells to heal. C. provides both adaptive and restorative functions. D. allows time for dreaming, which gives meaning and purpose to our daily lives. (VCAA 2004 Exam Q38)

Multiple choice - response It is generally accepted that sleep A. detoxifies the substances built up in the body during the day. B. allows time for damaged brain cells to heal. C. provides both adaptive and restorative functions. D. allows time for dreaming, which gives meaning and purpose to our daily lives. (VCAA 2004 Exam Q38)

Multiple choice - response David, a professional footballer, is physically exhausted after playing in all four quarters of the Grand Final. According to the restorative theory of sleep, in which stages of sleep would David be most likely to spend more time in the two nights sleep following the Grand Final? rapid eye movement (REM) non-rapid eye movement (NREM) stage 1 non-rapid eye movement (NREM) stages 1 and 3 non-rapid eye movement (NREM) stages 3 and 4 (VCAA 2011 Exam Q10)

Multiple choice - response David, a professional footballer, is physically exhausted after playing in all four quarters of the Grand Final. According to the restorative theory of sleep, in which stages of sleep would David be most likely to spend more time in the two nights sleep following the Grand Final? rapid eye movement (REM) non-rapid eye movement (NREM) stage 1 non-rapid eye movement (NREM) stages 1 and 3 non-rapid eye movement (NREM) stages 3 and 4 (VCAA 2011 Exam Q10)

Fast five: Question 1 Which theory supports the idea that sleep is necessary for survival?

Question 1 (Response) Which theory supports the idea that sleep is necessary for survival? Answer: Evolutionary

Fast five: Question 2 Which theory supports the idea that sleep is necessary for replenishment?

Question 2 (Response) Which theory supports the idea that sleep is necessary for replenishment? Answer: Restorative

Fast five: Question 3 Which type of sleep is thought to replenish the mind?

Question 3 (Response) Which type of sleep is thought to replenish the mind? Answer: REM

Fast five: Question 4 Which type of sleep in thought to replenish the body?

Question 4 (Response) Which type of sleep in thought to replenish the body? Answer: NREM

Fast five: Question 5 Refutive evidence for evolutionary theory states that whilst asleep animals are…

Question 5 (Response) Refutive evidence for evolutionary theory states that whilst asleep animals are… Answer: More vulnerable to attack /unable to protect themselves

Sleep across the lifespan VCE PSYCHOLOGY UNIT 4 Sleep across the lifespan Presented by Kristy Kendall Study design dot point: the differences in sleep across the lifespan and how these can be explained with reference to the total amount of sleep and changes in a typical pattern of sleep (proportion of REM and NREM) .

Sleep across the lifespan Sleep patterns change with age. You probably do not need as much sleep now as you used to and can go to bed later than when you were little. Newborns spend about 16 hours per day sleeping, with about half of this time in REM sleep. Young children also spend a lot of time in deep NREM sleep, but as they grow up the type of sleep they experience changes. Evidence suggests that REM sleep helps with brain development, particularly in early life. This would explain why infants need so much more. Adults sleep for about 8 hours, with about a quarter of this in REM sleep. By the age of 60 years, very little time, if any, is spent in stage 4 NREM sleep, with sleep lasting for about 6 hours – still with 20–25 per cent in REM sleep.

As we can see in Figure 14.7, the amount of REM sleep we experience decreases as we get older. Although this does not mean we need less sleep, rather it means our sleep becomes more fragile.

Sleep by age Babies approximately 16 hours per day by 1 year they sleep about 12-13 hours. 3-5 yr olds sleep 10-12 hours. Teenagers need 9-10 hours Adults (from 20 yrs) require approx 8 hours. Elderly need only 5-7 hours. Images used under license from Pixabay

How much sleep do you need?

REM vs NREM Babies – REM 50% to NREM 50% Childhood to adulthood – REM 20% to NREM 80% Old age – REM 15% to NREM 85%

Why does this occur? Total amount of sleep is relative to: - Production of growth hormone - Development of circadian rhythms Distribution of NREM to REM is relative to: - Replenishment needs (restoration theory)

Proportion of REM and NREM sleep in a typical pattern of sleep sleep cycles consist of REM sleep and NREM sleep. NREM sleep is broken down into stages 1, 2, 3 and 4. When we first fall asleep, we tend to experience NREM stage 1, then stage 2, stage 3, stage 4, stage 3, stage 2 and finally REM sleep. This is our first NREM/REM cycle and lasts for about 90 minutes. After the first NREM/REM cycle, we often skip stage 1 NREM sleep and enter stage 2 NREM sleep again. We then descend through stages 3 and 4 NREM sleep before returning via stage 3 to Stage 2 to REM sleep. This cycle can be plotted on a graph known as a hypnogram Return to stage 2 NREM sleep marks the start of the third cycle and, this time, we stay in this stage for about an hour, often not descending into stages 3 and 4 NREM sleep. We spend a longer period of time in REM sleep and, again, the end of REM sleep marks the end of the cycle. The fourth, fifth and (sometimes) sixth cycles are similar; we are unlikely to enter stages 3 and 4 NREM sleep and increasingly more time is spent in REM sleep. We have a tendency to wake briefly (usually without conscious awareness) before or after a period of REM sleep. We might wake up in the fifth sleep cycle, either directly from stage 2 NREM sleep or REM sleep, but often roll over and go back to sleep and start another cycle.

While the exact pattern of sleep varies from person to person and from night tonight, the following features are the same: stages 3 and 4 NREM sleep typically occur in the first two cycles of the NREM/REM sleep cycle we spend more time in REM sleep as the night progresses.

Sleep during adolescence There is so much evidence about the benefits of sleep and the dangers of not getting enough sleep during adolescence. Tips for getting sleep: - Routine - Diet/exercise - Light cues/triggers - Disruptable technology How much sleep do you need? https://www.youtube.com/watch?v=SVQlcxiQlzI Source: en.wikipedia.org

Multiple choice activity As a person ages, the total amount of time that they spend asleep each night decreases, while the proportion of time spent in REM sleep increases. decreases, while the proportion of time spent in NREM sleep increases. increases, while the proportion of time spent in REM sleep also increases. does not change in relation to the percentage of time spent in REM sleep and NREM sleep. (VCAA 2014 Exam Q24)

Multiple choice activity The proportion of rapid eye movement (REM) sleep to non-rapid eye movement (NREM) sleep is equal across the life span. greater in infancy than later in the life span. lower at birth and equal in later adolescence. lower at birth and higher in late adolescence. (VCAA 2013 Exam Q4)

Multiple choice activity The following graphs show the typical sleep cycles for two distinct age groups. The typical sleep cycles represented in graphs 1 and 2, in order, are: infant, adolescent. infant, elderly person. elderly person, infant. adolescent, elderly person. (VCAA 2013 Sample Exam Q3)