Week 1 - Sleep: What is it, how much do we need and how do we measure it? Flashcards
What is sleep?
“sleep is a reversible behavioural state of perceptual disengagement from and unresponsiveness to the environment.”
The gold standard of objectively measuring sleep is polysomnography (PSG)
What are the objective and subjective measures of sleep?
Objective
- polysomnogrpaphy (sleep architecture)
- Actigraphy (indirect)
Subjective
- Sleep Diary
What are the key features which Polysomnography (PSG) measures?
an objective measure of sleep which can be conducted at home or in a lab.
- sleep latency
- sleep time
- number of awakenings
- sleep efficiency
- sleep architecture
What are the key features of Polysomnography (PSG)?
an objective measure of sleep which can be conducted at home or in a lab.
- sleep latency (how long it takes to fall asleep)
- sleep time
- number of awakenings
- WASO - waking after sleep onset (minutes awake)
- sleep efficiency
- sleep architecture
Describe the features of using a sleep diary to measure sleep.
Subjective measure.
- sleep latency, quality, efficiency, time
- awakenings
- day time sleeping
What is actigraphy?
Wrist device which measures sleep. No movement = asleep. e.g. smart watch
What are the two distinct stages of sleep?
- Rapid eye movement (REM)
2. Non-REM
Describe rapid eye movement (REM) sleep
EEG activation, muscle atonia, and episodic bursts of rapid eye movements.
An activated brain in a paralyzed body. –> no muscle activity
A.K.A Jerky eye movement (JEM) sleep
Describe NREM sleep
Stage of sleep which has four stages and is a relatively inactive yet actively regulating brain in a movable body.
muscle activity - body might jerk
Which sleep stage does dreaming occur?
REM
True or false, the arousal thresholds in NREM sleep are greatest in stage 1 and lowest in stage 4.
False, they are highest in stage 4.
How would you describe the EEG pattern in REM sleep?
- active
- desynchronised
- paradoxical
___ sleep is used to describe NREM in infants and ___ describes NREM sleep in animals.
- quiet sleep
2. synchronised sleep
Onset of sleep is indicated by the ___ stage. Therefore, abnormal sleep conditions such as narcolepsy are diagnosed when sleep onset occurs in the ___ stage.
Onset of sleep is indicated by the NREM stage. Therefore, abnormal sleep conditions such as narcolepsy are diagnosed when sleep onset occurs in the REM stage.
What are the three polysomnographic measures of sleep
- Electroncephalogram (EEG)
- Electrooculogram (EOG)
- Electromyogram (EMG)
What does Electroncephalogram (EEG) measure?
measures brain activity to determine sleep ONSET and sleep STAGES
What does Electrooculogram (EOG) measure?
EOG signals represent the electrical activity of the eyeball and eyelid motions recorded by measuring the potential difference between the cornea and the fundus of the eye
- criteria for staging REM sleep (uses info from eye movement)
- sleep onset
What does Electromyogram (EMG) measure? How is it related to atonia?
- for staging REM
EMG (usually placed on the chin) is used to record atonia (loss of muscle strength) during REM sleep or lack of atonia in patients with REM-related parasomnias (e.g. lack of paralysis during REM sleep thus moving/acting out dreams)
How does EEG measure brain waves?
- using several electrodes that are attached to your scalp reflect brain waves
- The technician will measure your head and mark where to place the electrodes
- 16 and 25 electrodes will be attached to your scalp with a special paste - electrodes must be places on opposite ends/ one active part, another inactive
- reflects the summation of synchronous activity across many neurons
- Many neurons (synchronous as a single voltage change in a single neuron is too small to detect)
How does EEG measure brain waves?
- reflects the summation of synchronous activity across many neurons
- Many neurons (synchronous as a single voltage change in a single neuron is too small to detect)
- looking at the difference in electrical potential between pairs of electrodes placed on scalp
What does an EEG trace show?
Y axis - voltage (microvaults, μV)
X axis - time (seconds)
Which two elements are used to measure brain waves in an EEG?
amplitude (how big a wave is)
Frequency (how many )
Hz - cycles per second
Which waves are associated with being awake?
Gamma
Beta
Some Alpha
Which waves are associated with being asleep
some Alpha
Theta
Delta
How many hertz/ Hz/ cycles do Gamma waves have?
30-100hz
How many hertz/ Hz/ cycles per second do Gamma waves have?
30-100 hz/cps
- unsynchronised firing
How many hertz/ Hz/ cycles do Beta waves have?
13-19 hz/cps
- alert waking activity, arousal from sleep
- sigma activity: 11 -16 hz sleep spindles
How many hertz/ Hz/ cycles do Alpha waves have?
8-12hz/cps
- relaxed waking, eyes closed, arousal from sleep
How many hertz/ Hz/ cycles do Theta waves have?
4-7 hz/cps
- sleep onset, light sleep
How many hertz/ Hz/ cycles do Delta waves have?
- 5-4 hz/cps
- deep sleep
- synchronous, slow wave activity (fire together, slow down together)
- minimum amplitude
What are the components of sleep microarchitecture?
Sleep spindle - N2 Sleep, Theta waves, fast burst of activity, memory consolidation
K-complex - sudden bursts in synchronous activity, slow moving, memory consolidation, suppression of cortical arousal
Vertex sharp wave - Theta like wave observed at sleep onset - unknown function, seen in epilepsy
How are K-complexes indicative of the importance of sleep?
They suppress cortical arouse thus sleep is important because we have developed an in-built mechanism to protect the sleep state.
What are to microaahitectral components observed in N2 sleep?
K-complex and sleep spindles
A hypnogram is a part of sleep architecture.
Define hypnogram and its key features?
A hypnogram is a form of polysomnography; it is a graph that represents the stages of sleep as a function of time.
- N1-N3/4 stages of sleep + REM
- the organisation/ composition of sleep
- NREM and REM sleep alternate ~ every 90mins
The R&K method of sleep architecture/ analysis uses ___ stages of sleep and the AASM uses ___ stages
The R&K method of sleep architecture/ analysis uses 4 stages of sleep and the AASM uses 3 stages
Sleep cycles typically last about 90 min. Approximately how many do people have per night?
4-5 sleep cycles per night
What are some changes which occur in the body during REM sleep?
- inhibition of sensory input and motor output
- muscle twitching, penile erection
- autonomic functions - fine control of temperature, cardiopulmonary function impaired
- vivid, realistic dreaming
____, ____ and ___ are not exactly efficient measures of sleep in sleep diaries compared to polysomnography
sleep latency, sleep onset and number of awakenings are not exactly efficient measures of sleep in sleep diaries compared to polysomnography
What is the two process model of sleep regulation?
- Homeostatic Process
- for each hour awake, drive to sleep incrementally increases
- sleep onset = restoration of sleep equilibrium - Circadian rhythm process
- simultaneous natural system which includes a 24hr system of promoting wake and sleep
- “post lunch dip” is a result of the wake promoting system decreasing in the afternoon (peaks again in the evening)
- Melatonin promotes drive to sleep in the evening when lights are off
What is the post lunch dip?
occurs even when the individual has had no lunch and is unaware of the time of day
part of the circadian system
Describe the paradoxical relationship between circadian drive for sleep and habitual sleep time
- Peak in circadian drive for wakefulness in the evening - to counter the drive to sleep (wake maintenance zone)
- Peak in circadian drive for sleep in the early morning - homeostatic signal low [sleep pressure relived] ( circadian trough)
Why do we sleep?
- it is fundamental across many systems in the body - gut, pancreas, brain
- evolutionary constant across all animals (e.g. eat, sleep, move) despite dangers
- fully sleep deprived animals die but humans can not sleep for 11+ days and won’t die
- Restorative: growth hormones, brain plasticity, flushing waste from brain, brain function
What are the theories related to the function of sleep?
Enhance Survival/ Adaptation (inactivity theory)
- protected from predators
active at night.
- not a lot of evidence
supporting theory as it
isn't universal across
species
Energy Conservation Theory - need to save energy for tasks needed for survival e.g. hunting, running from predators
Restorative theory
- metabolism
- optimal brain functioning
- neuroplasticity + memory
consolidation
- flushing of toxins
“by the brain, for the brain” VS whole system
- sleep is about restoration of body temperature, restoring the brain (1990s)
- all systems are restored e.g. metabolism, not just brain function
According to research, are people more likely to get more sleep during the weekdays or weekends?
What is the duration of sleep and why do we get more sleep during X?
- more sleep on the weekend
- 6 hours 40 & 7 hours 07 respectively
- More time to sleep on weekends + catching up on missed sleep
How do we measure how much sleep is needed using observational studies?
- sleep historically (we sleep less compared to past)
- sleep duration and disease
risk (dose response ratio) - sleep on a weekend (catching up on sleep)
What point refutes the claim that we need X amount of sleep because in modern times, we sleep less than previous times due to technological advances
Historical observational studies - we don’t know which period of time to compare with because in previous times, we lost sleep due to other factors e.g. war, The Great Depression
sleep duration during work days and free days
According to observational studies, how much sleep do we need?
7.5-9.5hrs
What are the experimental studies which tell us how much sleep we need?
- Ad lib time to sleep (sleep as much as you want and sleep duration = how much sleep needed)
- dose response changes in sleep & performance
According to experimental studies, how much sleep do we need?
Ad lib study In 24hrs:
- older ppl: 7.4h (7-9h)
- younger 8.9h (6.1-10.3)
12 hrs:
- older (6.4hr)
- younger (7.9h)
Dose response
-8.16hs
