C

Lecture 2

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

Type

Measurement

Function

EOG

Eye movements

Categorize REM sleep or SWS

EMG

Muscle tonus

Detect REM sleep + diagnosis of sleep disorders

EKG

Heart rate

Diagnosis of cardiac anomalities in sleep

EEG

Brain’s electrical activity

Detect sleep onset, sleep stages and detection of anomalies

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

Wake

Resting wake, eyes closed

Sleep onset, NREM1, NREM2, REM

NREM3

Beta

Alpha

Theta

Delta

13-30 Hz

8-13 Hz

4-8 Hz

0.5-4 Hz

Desynchronized: low amplitude

Synchronized: high amplitude

Spatial and Temporal Resolution Comparisons

  • Spatial resolution: location in the brain

  • Temporal resolution: how quickly it can detect changes

Sleep Stages

Stages

%

Infos

Sleep onset

-

Gradual process
Neurons stop firing for fractions of seconds

NREM1

5

General slowing of brain activity
Eye movements - rolling
Diminished responsiveness
Hypnagogic imagery - sensations, images, sounds

NREM2

50

Mental activity range from simple to complex
Presence of sleep spindles and K-complexes

NREM3

15

Brain activity is slow and synchronized
Parasomnias (night terrors + sleepwalking)

REM

25

Mixed frequencies
Muscle atonia/paralysis
Rapid and saccadic eye movements
2 phases: tonic + phasic (eye movements)
Breathing and cardiac activity are irregular
Dreams + nightmares
Realistic and engaging mental activity

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