Sleep and Dreams

• Circadian rhythms are the body's natural processes that vary over a 24-hour cycle e.g. the sleep-wake cycle.
• The area of the brain that controls our circadian rhythms in the hypothalamus, and in particular a part of the hypothalamus called the suprachiasmatic nucleus (SCN).
• The SCN controls melatonin, a hormone that makes us feel sleepy.
• Melatonin is released into the bloodstream when it starts to get dark.
• Melatonin makes a person feel drowsy and eventually fall asleep.
• Melatonin levels peak in the middle of the night then decrease towards daytime.
• Melatonin supplements are sometimes given to children or adults with sleep problems.
• Adenosine builds up in our neurones during the day, this also causes us to feel gradually more tired as the day goes on.
• Caffeine blocks adenosine receptors in neurons, making the body less responsive to the build-up of adenosine and reducing feelings of tiredness.
• Stage 1 - Drifting off/easily woken
• Stage 2 - Sleeping soundly
• Stage 3 - EEG brain monitor begins to show some delta waves
• Stage 4 - Groggy and disorientated if woken
• REM sleep - REM sleep is the most active stage of sleep, characterized by rapid eye movement and dreaming.
• Aim of Demment and Kleitman (1957)

  They aimed to understand the function of REM sleep, and whether eye movements were connected to the content of dreams.
• Method of Dement and Kleitman (1957)


  9 adults (7 male, 2 female) came to a sleep lab for a polysomnography, having avoided alcohol and caffeine during the day. They were woken several times during the night by the researchers and asked if they had been dreaming, and if so what their dream had been about and how long it had lasted.
• Findings of Dement and Kleitman (1957)


  The participants said that they had been dreaming if woken during REM sleep on almost 80% of wakings, compared to around 9% if woken up during non-REM sleep. They also said that their dream had been shorter if they were woken 5 minutes after the start of REM sleep, compared to being woken 15 minutes after it started. Eye movements did appear to link to what participants had been dreaming about.
• Evaluation of Dement and Kleitman (1975)


  The study used a small sample, and its artificial setting may have affected the quality of sleep or the content of dreams. Evidence that REM sleep is dream sleep has been supported by subsequent research, but the findings linking dream content to eye movements have not. The study focused on adults, so the results can't be generalised to children.
• Zeigebers are exogenous time givers e.g. light and darkness.
• A polysomnography is a study that uses multiple measures of brain and bodily measures of brain and bodily processes during sleep. It uses and EEG to measure brain waves across the different sleep stages.
• Some people are more prone to early waking than others - some people call this group the 'lark'.
• Other people prefer sleeping later in the morning - these people are called owls.
• Most adults need around 7-8 hours of sleep per night to function well.
• Babies and young children need more sleep, with newborns sleeping for the majority of the time but shorter spells and much less deep.
• The amount of sleep needed reduces through the lifespan, with the lowest levels in old age.
• A few people can function well on six hours sleep or less, but most people who get a small of sleep are accumulating a sleep debt - a lack of sleep that they need to 'pay back' later.
• In adolescence, the body clock shifts gradually later until the mid to late teens, and then it starts to get earlier again.
• The SCN controls out body clock and triggers the release of melatonin.
• Adenosine builds up in our neurone as a natural by-product of the brain's daily activities, leading to fatigue later in the day.
• The brain cycles through REM and several non-REM sleep stages during the night, each with their own characteristics electrical activity in the brain.
• Sleep is important for the brain to stay in good health, and to consolidate memories.
• Oswald's (1966) restoration theory of sleep states that the main function of sleep is to allow the body and the brain to carry out repair tasks such as:

  • repairing minor bodily injuries
  • removal of waste chemicals in the muscles
  • replenishing neurotransmitters and/or energy in the brain
• Shapiro et al. (1981) studies runners and found that non-REM sleep rose from 25% to 45% of total sleep over the next two nights. This supports the idea that the body is using sleep time to repair minor damage.
• Adam and Oswald (1988) believed that the brain and body are restored in different sleep stages:

  • REM sleep allows the growth and reparation of neutrons and replenishment of neurotransmitters.
  • slow-wave sleep is essential for bodily restoration.
• Adam and Oswald's (1983) evidence included the following findings:

  • People who have had spinal operations or taken drug overdoses have longer periods of REM sleep, supporting the idea that this stage is essential for repairing the brain and other parts of the nervous system.
  • The level of neurotransmitters in the Brian reduces during the day, indicating that it needs to be replenished at night.
• The cognitive approach states that the purpose of sleep is to facilitate our cognition, for example by organising memories.
• Our key idea is that sleep facilities information processing. According to this view, switching off for a night's sleep allows new information to be sorted, stores and consolidated..
• A cognitive theory of dreaming is the reorganisation theory (Crick & Mitchison, 1968). It is based on reverse learning, meaning that learning can be undone during REM sleep. Crick and Mitchison proposed two categories of memories:

  • adaptive memories - useful memories
  • parasitic memories - harmful memories that lead to obsessions and compulsive behaviour.
• Crick & Mitchison (1986) believed that the cortex can become overloaded, and parasitic memories are deleted during sleep to make space. As random memories are activated, dreams are produced.
• Crick and Mitchison argued that reverse learning during REM sleep allows the brain to be smaller and more efficient. They supported this claim by referring to large-brained species that lack REM sleep e.g. dolphins.