Sleep and Dreaming Flashcards
Introduction - Sleep
Siegel (2008) defines sleep as a rapidly reversible state of immobility and greatly reduced sensory responsiveness. Essential part of life. Large portions of life spent sleeping. Assume that it fulfils a critical biological function. Sleep deprivation has an impact on both REM and slow-wave sleep
Describe REM sleep
Rapid eye movement (REM) accounts for 20-25% of the sleep cycle Low amplitude and high frequency EEG activity. Pattern similar to when the brain is awake. Fast eye movements, eyes move rapidly beneath closed eyes. Core muscles relaxed, increased variability in physiological function e.g. HR, blood pressure and breath rate.
Describe slow-wave sleep
Stages 3 and 4 of sleep cycle. Stage 3 = Body enters deeper stage of sleep. Occasional delta wave, stage 4 mostly delta waves. Stage 4 = Deepest form of sleep with lowest ability to generate arousal. Reduction in HR
Compare both REM and slow-wave sleep
Stage of sleep affects activity in the brain and body
- REM = Less body relaxation. Increase in HR compared to reduction in HR in slow-wave.
- EEG activity similar to when the brain is awake whereas slow-eave shows different.
Early evidence suggests REM responsible for dreaming.
- Dement and Wolper (1958) - Did things whilst participant slept e.g. throw water. Objects incorporated ended up being in dream.
- Large amount of evidence against this now e.g. anti-depressants suppress REM sleep, but ppl do not report reduced rates of dreaming.
What happens if you deprive an individual of REM sleep?
Default theory = Dangerous to stay in slow-wave for a long time which is why the body has stages.
Nykamp et al. (1998) - Studied effects of sleep deprivation in REM stage. Participants were awakened every time they entered REM sleep and had to stay awake for a further 15 minutes. Participants did not report feelings of tiredness despite having 5 hours sleep. No REM rebound. Suggests REM sleep not required.
Webb & Agnew (1967) - Participants had to be awakened 17 times in first night of REM sleep deprivation and 67 times during the 70th night. Suggests that the amount of REM sleep is regulated separately from amount of slow-wave sleep. REM sleep serves a special function. Suggested it is important for memory consolidation - leads acquired memory traces to stabilise.
Rasch et al. (2004) - SSRIs reduce REM but no effect on finger tapping performance. Perform better on memory tasks even though have no REM sleep.
Describe what happens if you deprive an individual of slow-wave sleep
- Short sleepers tend to get as much slow-wave sleep as people who sleep for longer periods
- Reducing sleep time results in reduction in stages 1 and 2, but not slow-wave.
- Sleep deprivation leads to an increase in sleep efficiency where slow-wave sleep is prioritised.
- Suggests that slow-wave sleep is important/has a restorative capability.
Describe the different theories of sleep
Recuperation theory
- Being awake depletes energy resources by disrupting homeostasis.
- Sleep is the act of returning us to baseline levels.
- Slow-wave activates the rest and digest systems.
- Explains why we need to have a lot more sleep after not having much for a while.
- E.g. Xie et al. (2013) - Theory that sleep removes neurotoxic waste products which arise in the awake brain. Neurotoxic waste is a range of proteins linked to neurodegenerative disease.
Adaptation Theory
- Argues that sleep is a reaction to the internal 24-hour timing system that evolution has primed us for. Programmed to sleep at night regardless of what happens during the day.
- Focuses on when we sleep. - Humans not well adapted to life in dark, sleep at night to conserve resources.
- Motivated to sleep, but don’t need it to survive and don’t need a certain amount of sleep.
- Sleep related to how vulnerable a species is whilst sleeping and how much time it needs to spend to feed itself and take care of survival characteristics e.g. Zebras sleep for 2 hours a day and must continuously graze to eat enough.
What effect dies sleep deprivation have on decision making?
Iowa gambling task
- Test of risky decision making
- Those with frontal damage drawn to bad decks.
- Led to suggestion that sleep deprivation reduces activity in the vmPFC and patients with damage here show increased anger, less empathy.
Killgore et al. (2006)
- Looking at if sleep deprivation has negative impact on decision making in iowa task.
- Perform at baseline and then awake for 49 hours.
- Need an extreme amount of sleep deprivation in order to see results
Describe what animal studies show about sleep deprivation
Carousel apparatus to deprive rats of sleep. Hooked up to an EEG and each time it detects they are sleeping, they are thrown into water.
Sleep deprived rats die after 12 days. Died from stress, not due to lack of sleep. Difficult to study in animals.
Describe Insomnia
Report that it takes hours to sleep, but when tested they sleep for longer than described.
Sleep apnoea often misdiagnosed as insomnia. Unaware that often awake.
Periodic limb syndrome - Involuntary and unaware limb movements associated with feelings of having slept poorly. Report poor sleep, but unaware of problem.
Describe Hypersomnia
Most commonly studied form is narcolepsy = severe daytime sleepiness and daytime sleep episodes. Only spend an hour more sleeping. Sleep at inappropriate times.
- Gene found to contribute Orexin. Reduced levels in cerebrospinal fluid and brain.
- Synthesised in brain by neurons in hypothalamus. Region linked to promotion of wakefulness.
Cataplexy - Recurring losses of muscle tone during wakefulness triggered by emotional experiences. Results in daytime sleepiness, sleep paralysis and hypnagogic hallucinations.
What are the effects of long-term sleep reducing and what are the differences between short and long-term sleepers?
Long-term sleep reducing = High plasticity. People can adjust to some degree of sleep deprivation. Sleep becomes more efficient after prolonged burst of sleep deprivation.
Fichten et al. (2004) - Compared sleepers. Long sleepers sleep more and short sleep less. No evidence that short sleepers were suffering.
Friedman et al. (1997) - Reduced sleep over 9 weeks and then reduced duration over a year. Sleep efficiency increased. Consistent with plasticity of sleep. However, small sample size.
Tamakoshi & Ohno (2004) Sleep and health
Sleeping 8 hours not as healthy as proposed Fewest deaths between 5-7 hours. However, correlational data. Doesn’t prove that sleeping 8+ hours causes health problems.
Describe the stage of wakefullness
Beta activity is rapid and low voltage. Alpha activity occurs just before sleep. There is higher voltage and lower frequency.
Describe stage 1 of sleep
- Low voltage - High frequency - Similar but slower to alert wakefulness - Lower HR and reduction of muscle tension
