3.5 Problem 3: Sleep
Carskadon: Normal Human Sleep
Sleep Definitions
Sleep = reversible behavioural state of perceptual disengagement from and
unresponsiveness to the environment
Within sleep, 2 separate states have been defined: rapid-eye movement (REM) and
non-REM (NREM)
NREM = 4 stages defined along the electroencephalogram (EEG)
- EEG pattern during NREM is synchronous, characterized by sleep spindles, K-
complexes, and high-voltage slow waves
- Arousal thresholds lowest in stage 1, highest in stage 4
REM sleep defined by EEG activation, muscle atonia (reduced muscle tonia in
body’s muscles), and episodic bursts of rapid eye movements
- REM sleep usually not divided into stages, although tonic & phasic types of REM
sleep are occasionally distinguished
- Bursts of ponto-geniculo-occipital (PGO) waves, which are accompanied by
rapid eye movements, twitching of distal muscles, middle ear muscle activity, and
other phasic event markers
- Activated brain in a paralyzed body
Sleep Onset
Definition of sleep onset: difficult to define
Electromyogram (EMG): may show gradual decrease of muscle tonus as sleep
approaches, but changes in EMG don’t really pinpoint sleep onset. Pre-sleep level of
EMG, particularly if person is relaxed, can be entirely indistinguishable from that of
unequivocal sleep
Electrooculogram (EOG): shows slow, possible asynchronous eye movements that
usually disappear within several minutes of EEG changes
Electroencephalogram (EEG):
- EEG changes from a pattern of clear rhythmic alpha activity, particularly in
occipital region, to relatively low-voltage, mixed-frequency pattern (stage 1 sleep)
- Stage 2 EEG patterns (K-complex or sleep spindle) may be needed to
acknowledge sleep onset
- Sleep onset does not often occur all at once; it’s difficult to accept a single
variable as marking
sleep onset
- Consensus that EEG
change to stage 1,
usually accompanied by
slow eye movements,
identifies transition to
sleep
Behavioural Concomitants of Sleep Onset
,Simple Behavioural Task
Volunteers asked to tap 2 switches alternately at a steady pace
This simple behaviour continues after onset of slow eye movements, may persist for
several seconds after EEG changes to a stage 1 sleep pattern
Behaviour then ceases, usually to recur only after the EEG reverts to a waking pattern
This is the simplest kind of ‘automatic’ behaviour pattern. This behaviour can persist
past sleep onset, could explain how impaired, drowsy drivers are able to continue
down the highway
Visual Response
Bright light placed in front of subject’s eyes, they are asked to respond when a light
flash is seen by pressing a microswitch
When EEG pattern is stage 1/stage 2 sleep, response is absent more than 85% of the
time
Subjects say they didn’t see the light flash, not that they saw the flash, but response
was inhibited
Auditory Response
Series of tones played over earphones, subject is told to respond every time they hear
a tone
Reaction times became longer in proximity to onset of stage 1 sleep, and responses
were absent with change in EEG
Response after sleep-related disappearance typically requires resumption of waking
EEG pattern
Olfactory Response
When sleeping people are asked to respond when they smell something, response
depends on sleep state and on particular odorant
Responses to peppermint & pyridine were well maintained during initial stage 1 sleep
Peppermint not consciously smelled in stages 2 & 4 NREM sleep or in REM sleep
Olfactory system of humans is not a good sentinel system during sleep
Response to Meaningful Stimuli
Meaningful vs. nonmeaningful stimuli
Lower arousal threshold for our own name vs. someone else’s name. In light sleep,
one’s own name spoken softly will produce an arousal, a nonmeaningful stimulus will
not. A sleeping mother is more likely to hear her own baby’s cry than the cry of an
unrelated infant
It’s clear that sensory processing at some level does continue after onset of sleep
Hypnic Myoclonia
General/localized muscle contraction very often associated with rather vivid visual
imagery
Tend to occur more commonly in association with stress or with unusual/irregular
sleep schedules
Instead of REM motor inhibitory component, they get imagery component of REM
sleep (hypnagogic hallucination). Response to the image results in a movement/jerk
Memory Near Sleep Onset
, Transition from wake to sleep tends to produce a memory impairment
Sleep could close the gate between short-term & long-term memory stores
Can recall words if asked 30 seconds after waking, but not 10 minutes
Memory is impaired by sleep
In 30 second condition, both longer-term (4-10 minutes) & shorter term (0-3 minutes)
memory stores remained accessible
In 10 minute condition, words that were in longer-term stores (4-10 minutes) before
sleep onset were accessible, but words that were still in shorter-term stores (0-3
minutes) at sleep onset were no longer accessible (they had not been consolidated into
longer-term memory stores)
Sleep inactivates transfer of storage from short to long-term memory
If sleep persists for about 10 minutes, memory is lost for the few minutes before sleep
Progression of Sleep Across the Night
Pattern of sleep in a normal young adult
- Normal adult enters sleep through NREM sleep, REM sleep doesn’t occur until 80
minutes, and NREM sleep and REM sleep alternate through the night, with
approximately 90-minute cycle
First Sleep Cycle
Stage 1 sleep: usually persists for a only a few (1-7) minutes at onset of sleep
- Sleep is easily discontinued at this stage, e.g., by softly calling their name,
touching them lightly, etc.
- Stage 1 sleep is associated with low arousal threshold
- Stage 1 sleep occurs as a transitional stage throughout the night
- Common sign of severely disrupted sleep is an increase in amount of stage 1 sleep
Stage 2 NREM sleep: signaled by sleep spindles/K-complexes in EEG
- Approximately 10-25 minutes
- More intense stimulus is required to produce arousal
- Same stimulus that produced arousal in stage 1 sleep often results in an evoked K-
complex but no awakening in stage 2 sleep
Stage 3 NREM sleep: high-voltage, slow-wave activity gradually appears
- Usually only lasts a few minutes
- Accounts for more than 20% but less than 50% of EEG activity
- Transitional to stage 4, as more high-voltage slow-wave activity occurs
Stage 4 NREM sleep: comprises of more than 50% of the record
- Usually lasts about 20-40 minutes
