Studying Sleep

Subjective Estimation

Retrospective

• Questionnaires (Pittsburgh Sleep Quality Index) or Interviews

• Pros: easy to get

• Cons: often unreliable, subject to bias

Prospective

• Sleep diaries

• Pros: can be modified to target a specific sleep problem

• Cons: labour-intensive, require motivation, captures limited subjective information

Objective Measures

Actigraphy

• Measures gross levels of motor activity

• Estimate sleep-wake patterns → sleep fragmentation

• Pros: non-invasive, can be used at home

• Cons: records activity-rest patterns so limited sleep data

Video Recording

• Observe motor activity at night

• Pros: cheap

Brain Imaging

• Often done when people are sleep deprived so they fall asleep easily

• Cons: uncomfortable, invasive, expensive

Functional Near-Infrared Spectroscopy

• Measures hemoglobin concentration

• Pros: non-invasive, portable

Portable EEG

• Oura: measures heart rate variability and body temperature

Depth Electrodes

• Record sleep patterns

• Used in the context of pre-operative or diagnostic epilepsy non-responsive to medication

• Implanted for many days

Single Cell Recordings

• Pros: very precise

• Cons: very invasive → only for animals

Polysomnography

EEG

• Waves:

  • Amplitude: deviation from the baseline

    • Measures the synchrony of neurons

  • Frequency: number of cycles per second

    • Measures the speed of discharge of neurons

• EEG signal: aggregated activity of thousands of pyramidal neurons perpendicular to the scull

• Frequencies

  • There is never just 1 frequency present

  • Many frequencies are combined

  • There is usually a dominant frequency

• Frequency bands

Spatial and Temporal Resolution Comparisons

• Spatial resolution: location in the brain

• Temporal resolution: how quickly it can detect changes

Sleep Stages

Sleep Spindles

• Sigma activity

• Plays a role in memory consolidation

• Associated with protective processes against neurodegeneration and brain plasticity

K-Complex

• Bipolar wave of 0.5 seconds

• Plays a role in thalamo-cortical gating

• Involved in preserving sleep

General Information

• The face only gets completely relaxed in REM sleep

• The vast majority of sleep is in theta frequency

• The duration of REM sleep increases as the night passes

• NREM3 or SWS is predominant during the 1st half of the night because it is the most important

• If we wake up during NREM3, we feel confused and cranky

• Babies develop muscle atonia, they are not born with it