Wk 1: Sleep introduction

  1. Why do we sleep?
    • Not fully understood
    • Sleep is restorative: growth hormone surge during sleep, brain plasticity (forming skills and memories)
    • Necessary for proper functioning: lack of sleep is associated with illness and impaired functioning
    • Flushing metabolic waste from the brain
    • Conserve energy
    • Enhance survival/adaptation
    • Restorative/repair of injury (NREM)
    • Aid learning/memory consolidation (REM)
  2. Sleep following brain injury (traumatic brain injury TBI)
    • People with TBI sleep for same amount but poorer quality
    • Stage 1 and 2 similar with control
    • Higher deep sleep
    • Lower REM
  3. Sleep and memory consolidation
    • Tower of Hanoi task: move disks into certain arrangement in the least amount of moves
    • Improved after 1 week retested (40% improvement- learned)
    • When REM is experimentally reduced the night after training, no improvement
  4. How much sleep do we need?
    • Adults should sleep 7 or more hours per night on a regular basis to promote optimal health.
    • Sleeping less than 7 hours per night on a regular basis is associated with adverse health outcomes, including weight gain and obesity, diabetes, hypertension, heart disease and stroke, depression, and increased risk of death. Impaired immune function, increased pain, impaired performance, increased errors, and greater risk of accidents.
    • • Sleeping more than 9 hours per night on a regular basis may be appropriate for young adults, individuals recovering from sleep debt, and individuals with illnesses.
    • For others, it is uncertain whether sleeping more than 9 hours per night is associated with health risk.
  5. Sleep 'need'
    • Individual differences
    • Some function well on 6 hours, some need >9 hours
    • Average need for optimal functioning, likely ~7.5 hours of SLEEP
    • Developmental changes in sleep need adolescent vs old
    • Good measure of adequacy of sleep is quality of wake time
  6. Measuring sleep
    • Objective measures:
    • Polysomnography (PSG): primarily in labs, measures sleep time, sleep stages
    • Actigraphy (indirect): eg fitbit
    • Subjective measures:
    • Sleep diary: Sleep latency, total sleep time, sleep efficiency
    • Sleep-report questionnaires: Pittsburgh Sleep Quality Index (global sleep quality)
    • Epworth Sleepiness Scale (trait sleepiness)
    • Karolinska Sleepiness Scale (state sleepiness)
  7. What does EEG measure?
    • Difference in electrical potential between pairs of electrodes placed on the scalp.
    • An EEG trace shows us: – Y axis – voltage (specifically µV)
    • – X axis – time (seconds)
    • Signals reflect postsynaptic potentials in several neurons.
    •  Signals are amplified and filtered to produce analog or digital recording.
    • Waves are measured by
    • amplitude and frequency (Hertz OR cycles per second)
    • Neurons not synced during REM
  8. Brainwave activity- EEG frequency bands
    • Gamma waves: 30-100 Hz
    • Beta waves: 13-29 Hz
    • Alert waking activity
    • Alpha waves: 8-12 Hz
    • Relaxed waking, eyes closed
    • Theta: 4-7 Hz
    • Sleep onset, light sleep
    • Delta: 0-4 Hz
    • Deep sleep, high amplitude
  9. Scoring sleep by epochs
    30 second measures
  10. Vigilant wakefulness
    • Beta activity
    • Desynchronised brain activity
    • High frequency
    • Low amplitude
  11. Relaxed wakefulness
    • EEG: low voltage, mixed frequency; rhythmic alpha activity (8-13 Hz)
    • EOG: some eye movements when drowsy
    • EMG: relatively high level of tonic activity, affected by voluntary movements
  12. Stage N1 sleep
    • EEG: low voltage, mixed frequency, may be theta activity (4-7 hz), vertex shap waves
    • EOG: SEMs
    • EMG: may be slight decrease from waking
  13. Stage N2 sleep
    • EEG: low voltage, mixed frequency (8-15 Hx)
    • Sleep spindles
    • K complex: negative sharp followed immediately by slower positive component
  14. Stage N3 sleep
    • EEG: high amplitude, slow wave activity (delta) less than 2 hz
    • EOG: none
    • EMG: low
  15. REM sleep
    • EEG: low amplitude, mixed frequency
    • EOG: REMS
    • EMG: low EMG tone (phasic twitches
  16. Typical sleep architecture across the night
    • Normal sleep is entered through NREM
    • Episodes of NREM and REM sleep alternate about every 90 mins
    • Stage 3/4 (N3) more prominent in first third
    • REM more prominent in second half
    • Image Upload 1
  17. "normal" sleep in young
    • Latency of 10-30min
    • Few, brief awakenings
    • Total sleep time (7-9h)
    • Sleep efficiency >85%
    • Full alertness throughout waking day
  18. Age related changes in sleep
    • Less slow wave (deep) sleep
    • Decreased arousal threshold
    • Increased awakenings
    • Unclear if need for sleep decreases; ability to obtain sleep does decrease
  19. Interaction between two processes
    • Paradoxical phase relationship between circadian drive for sleep and habitual sleep time in normal conditions:
    • – Peak in circadian drive for wakefulness in the evening.
    • – Peak in circadian drive for sleep in the early morning.
    • Circadian drive for wakefulness opposes homeostatic drive for sleep in the evening (just prior to normal bedtime) – helps maintain wakefulness
    • Circadian drive for sleep increases as homeostatic drive for sleep declines over course of sleep episode – helps maintain consolidated sleep
Card Set
Wk 1: Sleep introduction
Wk 1: Sleep introduction