Sleep 😴

• Sleep is an altered state of consciousness during which we are unresponsive to external stimuli
• It is considered an altered state of consciousness because our experience when we sleep is vastly different from when we are awake:

  • Lowered awareness
  • Reduced or restricted movement 
  • Dulled senses
  • Altered time perception (how fast/slow time passes) 

  Other ASC include alcohol induced, meditating, coma
• Without sleep: 

  • Can’t form or maintain the (neural) pathways in your brain that let you learn and create new memories
  • Harder to concentrate and respond quickly 
• Sleep is important to how nerve cells (neurons) communicate with each other. It also removes toxins from the brain (e.g., amyloid). 
• Evolutionary theory: sleep is a means of increasing an animal’s chances of survival in its environment

  • Animal’s sleep requirements have evolved over time for the species to hunt food, hide and conserve energy
  • The periods of wakefulness occur when it is safer to do so and sleeping when it is more hazardous to be awake
  • Sleep patterns have adapted in terms of whether the animal in question is a predator or prey, their food requirements and methods of defence from attack.
• Evolutionary theory - support (from the research of different animal species):

  Small animals (e.g., mice, possums)

  • Vulnerable to predators, sleep more so that they can hide from carnivores that will eat them
  • Hunt at night when they are less likely to be seen (evolved to have good night vision, increased hearing and smell, etc)

  Larger prey animals (e.g., deer) 

  • Sleep less because they are more exposed in their environment and need to be ready to escape from predators

  Animals with few natural predators (e.g., bears, lions)

  • Often sleep between 12 to 15 hours each day (or longer)
• Evolutionary theory - criticism: 

  • When asleep an organism has no awareness of its surroundings therefore making it more vulnerable to predators
• Restoration theory: proposes sleep allows our bodies to recover from the activities of the day. 

  Some things that occur during sleep are: 

  • Restocking resources that have been used up during the day
  • Repair to damaged cells, e.g. skin, muscles
  • Removal of built-up toxins in muscles
  • Release of growth hormones  (during deep sleep)
  • Consolidation of memories (make permanent)
  • Increases immunity to disease
  • Chemicals that regulate emotions are activated, enhancing mood
• Restoration theory - support: 

  • When we are unwell, we tend to sleep for longer.
  • People who are sleep deprived have higher incidence of illness.
  • Mood is lowered and emotions are harder to control when we do not get enough sleep.
• Restoration theory - criticism:

  People who do little exercise, including those bedridden or disabled, should sleep less, however do not, as their sleep patterns are similar to those of active individuals. The need for sleep is not reduced with lack of exercise. 
• Sleep cycle = Ultradian 

  Sleep-wake cycle = Circadian 
• Circadian rhythm (the sleep-wake cycle in humans follows this): 

  • Involves changes in bodily functions that occur within a duration of approximately 24hrs
  • Causes us to feel more alert in the day and less alert during the night
  • There is a ‘biological clock’ inside our brains that regulate the timing and activity of the sleep-wake cycle
  • The sleep cycle is influenced by environmental cues, especially levels of light.

  Circadian Rhythms are controlled by the pineal gland, (which receives information from retina in eyes)
• Pineal gland: 

  • Controls circadian rhythms 
  • About the size of a pea, named because it is shaped like a pinecone 
  • Receives information from the retina in the eyes about levels of light. This influences the secretion of the hormone melatonin. 

  People with damage to their pineal gland:

  • Often report changes to their circadian rhythms
  • May sleep more or less
  • Feel sleepy or restless at unusual times
• Melatonin: 

  • Responsible for making us feel sleepy
  • Low levels of light = more melatonin secreted
  • Higher levels of melatonin = increased drowsiness
  • Melatonin levels stay elevated throughout the night and fall back to low levels when it gets lighter in the morning 

  Melatonin is a hormone that induces sleepiness and drowsiness. It is secreted by the pineal gland in the brain when light levels are low, and its production decreases in the morning as light increases. This hormone helps regulate the body's sleep-wake cycle.
• Cortisol: 

  • A (stress) hormone that influences our sleep-wake cycle 
  • Increased cortisol = increased alertness

  In the morning as light levels increase, levels of cortisol increase leading to increased alertness and activity. Levels peak between about 9-10 am and are at their lowest at about 11pm-1am.
• Sleep episode = the total amount of time we spend asleep, made up of sleep cycles. 
• Sleep cycles: 

  • Make up sleep episodes
  • A typical adult has 5-6 per sleep episode
  • Consists of a period of NREM sleep (but not necessarily all four stages) and a REM sleep
  • On average they last for 90 minutes 
• NREM - Stage 1: 

  • Transition from being awake to being /falling asleep
  • May include hallucinatory images (e.g., flashes of light, feeling of falling, vivid images)
  • Hypnogogic jerks (involuntary muscle twitches that cause a jolt) are common
  • Generally lasts around 5 minutes
  • A very light sleep in which individuals can be easily awakened
• NREM - Stage 2:

  • Where “real” sleep begins (still considered to be a light sleep)
  • Body temperature begins to drop
  • Heart rate begins to slow
  • Lasts for about 10-15 minutes in the first sleep cycle and then gets longer with each cycle.
  • Makes up 50% of our total sleep
• NREM - Stage 3: 

  • A brief transition to the start of deep sleep 
  • Individuals are less responsive to external stimuli and more difficult to wake up
  • Unusual behaviours occur in this stage: sleep walking, sleep talking, sleep eating, night terrors
  • If woken from this stage, you will feel very groggy and disoriented
• NREM - Stage 4: 

  • Considered the deepest stage of sleep
  • Extremely difficult to wake someone up 
  • Awareness levels are very low (however individuals are still responsive to certain stimuli such as a smoke alarm or a baby crying)
  • Decreases in length and is usually only seen in the first and sometimes the second cycle of sleep
• REM - Rapid Eye Movement sleep:

  • The eyes move rapidly for short bursts of time
  • Considered a lighter sleep than NREM stages 3 and 4, therefore people are easier to wake from this stage
  • First REM stage lasts about 10 minutes in cycle 1 but the proportion of time spent in REM increases as the night progresses
  • Majority of dreams take place in REM
  • The final dream of the night tends to be the longest, strangest and most exciting
  • No muscle tension – the muscles that move voluntarily, especially those below the neck, are very relaxed to the point of being paralysed
• Hypnogram = A form of polysomnography; it is a graph that represents the stages of sleep as a function of time.
• Polysomnography = The recording of many physiological activities 
• EEG - electroencephalograph, measures the electrical activity of the brain

  EMG - electromyograph, measures the electrical activity of muscles

  EOG - electrooculograph, measures the electrical activity of the muscles that control our eye movements
• D: detects 

  A: amplifies 

  R: records

  E: electrical

  A: activity
• EEG - Electroencephalograph: 

  A device that detects, amplifies, and records the electrical activity of the brain in the form of brain waves
• Brain waves - EEG:

  • Alpha, delta, theta and beta waves

  Described by their amplitude and their frequency

  • Amplitude = the length and width of the waves 
  • Frequency = how many occurrences there are of that wave in a given time frame
• Awake and alert: Beta waves

  State of deep relaxation: Alpha waves

  
  

  NREM 1: Alpha and theta waves

  NREM 2: Theta waves (sleep spindles and K-complexes appear)

  NREM 3: Theta and less than 50% delta waves

  NREM 4: Theta and over 50% delta waves

  
  

  Stages 3 and 4 are often called slow-wave sleep (SWS) because of the slow frequency of the waves.

  
  

  REM: Beta-like waves
• Beta: High frequency, low amplitude

  Alpha: Medium frequency, medium amplitude

  Theta: Medium frequency (lower than alpha), medium amplitude (higher than alpha)

  Delta: Lowest frequency, highest amplitude 

  REM waves: Fast, sawtooth waves, beta-like, high frequency, low amplitude 

  
  

  Sleep spindles: Bursts of very high frequency waves

  K-complexes: A single wave of very high amplitude
• EMG - Electromyograph:

  A device that detects amplifies and records the electrical activity of muscles
• EOG - Electrooculograph:

  A device that detects amplifies and records the electrical activity of muscles that control eye movement
• In REM sleep, the EEG and EOG would show very high levels of activity, however the EMG would show very low levels of electrical activity. This is why REM is sometimes referred to as ‘paradoxical’ sleep. 
• Brain waves - sleep stages:

  A) Alpha, some theta

  B) Theta

  C) Theta, and >50% delta

  D) Theta, and <50% delta

  E) Similar to beta

  F) Medium frequency, medium amplitude

  G) Medium frequency, medium amplitude

  H) Low frequency, high amplitude

  I) Low frequency, high amplitude

  J) High frequency, low amplitude

  K) Very easy

  L) Fairly easy

  M) Difficult

  N) Difficult

  O) Fairly easy

  P) High

  Q) High

  R) Low

  S) Low

  T) Low

  U) Low

  V) Low

  W) Low

  X) Low

  Y) High

  Z) Reduced HR, and BR

  [) Reduced HR, and BR

  \) Reduced HR, and BR

  ]) Reduced HR, and BR

  ^) Increased heart rate, and breathing ratw

  
• Sleep and memory: 

  • Sleep plays a role in memory and learning
  • Our neural pathways are strengthened during sleep, increasing our learning and memory
  • Sleep (REM especially) plays a role in the consolidation of declarative memories
  • Sleep (stage 2 NREM especially) helps to establish our procedural memories
• Declarative Memory (also known as explicit memory): Involves facts, events, and information that can be consciously recalled and described in words. Knowing ‘that’ something… E.g., “I know that the capital of Victoria is Melbourne. 

  
  

  Procedural memory (also known as implicit memory): They are the memories or knowledge of how to do something. They are often difficult to put into words, and can be done without conscious awareness.

  -> A lack of sleep can lead to poor retention, slower speed, and reduced accuracy of motor tasks
• Sleep deprivation is defined as not getting enough sleep for our requirements. 

  
  

  It refers to not just the quantity, but also quality of sleep.
• Biological causes of sleep deprivation: 

  A biological cause can refer to an internal cause, such as genetic link, or the impact of hormones 

  • Illnesses, mental and physical 
  • Sleep disorders (e.g., insomnia)
  • Adolescent sleep shift
  • Alcohol addiction 
• Adolescent sleep shift:

  • Caused by the delayed release of melatonin during puberty 
  • Teenagers often don’t feel tired until 11pm and end up with a deficit of an average of 3 hours per night
• Lifestyle causes of sleep deprivation: 

  Lifestyle causes are adaptable factors in our environment