Lecture 8: Sleep and nightmares Flashcards
How can sleep be defined?
Sleep is a reversible behavioural state of perceptual disengagement from and unresponsiveness to the environment. Strange behaviours like sleepwalking, sleep talking and teeth grinding can occur.
How can different types of sleep be distinguished?
Between REM which is desynchronized, atonic muscles and dreaming, rapid bursts of eye movement and NREM which has consistent EEG activity (sleep spindles, K-complexes and high-voltage slow waves), low muscle tonus and minimal psychological activity.
What are the NREM stages?
1, 2, 3, 4 which are the same in the depth of sleep and the lowest arousal threshold in stage 1 and highest in stage 4
What is the difference between tonic vs phasic activity in REM?
Can be distinguished by the occurrence of rapid eye movements, muscle twitches and cardiorespiratory differences. Tonic activity has no rapid eye movements, muscle atonia and steady brain activity while phasic activity has intermittent bursts of activity, rapid eye movements, muscle twitches, and more variable physiological responses.
How is muscle atonia achieved?
Through inhibition of spinal motor neurons by brainstem mechanisms
How can sleep onset be defined by 3 different ways of measuring?
EMG: shows a gradual decline of muscle tonus as sleep approaches but not discrete and difficult to distinguish between pre-sleep
EOG: slow and asynchronous eye movements, which disappear after a few minutes. The onset of these coincide with perceived sleep onset
EEG: can move from clear alpha activity to a low-voltage mixed-frequency pattern. Specific EEG patterns like K complex or sleep spindles are needed for sleep onset. Sleep onset is more gradual so a single variable cannot mark this change
What are the behavioural correlates of the wake-to-sleep transition?
Simple behavioural task: when asked to do a simple task, the behaviour continues after the onset of slow eye movements and stops when EEG has a waking pattern
Visual response: bright light in front of eyes and in stage 1 or 2 of sleep reflect that they did not see the light-> perceptual disengagement
Auditory response: reaction times longer to tones while onset of stage 1 sleep and absent from change in EEG to sleep
Olfactory response: pleasant stimuli and unpleasant stimuli responses were maintained in stage 1 sleep. Peppermint was not recalled in stages 2 and 4, and pyridine never smelled in stage 4 but sometimes in stage 2
Response to meaningful stimuli: arousability shows differential responses to auditory stimuli, different responses to meaningful stimuli using K-complexes or arousal.
Hypnic Myoclonia: general or specific muscle contraction linked to vivid visual imagery, can occur with stress and irregular sleep
What has research found about the response to meaningful stimuli?
- lower arousal threshold needed for own name compared to another’s name
- likelihood of an appropriate response during sleep improved when nonmeaningful stimulus was made meaningful by linking absence to response to punishment
- regional brain activation occurs in response to stimuli and that different brain regions (temporal gyrus and OFC) were activated in response to meaningful stimuli
Why do hypnic myoclonias occur?
Can happen with dissociation of REM sleep components as the imagery components of REM can occur without the motor inhibitory component, which results in movements in response to the image
What is the usual transition into sleep?
For adults through NEM, while for infants is the REM portal
How does memory change near sleep onset?
The transition from wake to sleep produces a memory impairment. Word pairs were presented to volunteers at a 30 seconds or 10 mins after the onset of sleep and were asked to recall words, performance for 30 sec group was similar to before sleep onset-> STM and LTM stores were accessible but for 10 min group only LTM was inaccessible. Two interpretations: sleep inactivates transfer of storage from short to long-term memory or that encoding does not have enough strength to allow for recall. Sleep important for consolidation of perceptual and motor learning
Pattern of sleep in a healthy young adult
Enters sleep through NREM sleep, REM sleep occurs around 80 mins or longer after, then NREM and REM which alternate through the night with a 90 minute cycle. REM sleep episodes become longer through the night, with stage 3 and 4 taking less time in the second cycle and can disappear in later stages.
What occurs in the first sleep cycle?
- Stage 1 persists for a few minutes at the onset and can be easily discontinued, linked to a low arousal threshold. Can also be a transitional stage throughout the night
- Stage 2 is shown by sleep spindles or K-complexes in EEG and continues for 10-25 mins in first cycle. More intense stimulus needed for arousal (K-complex can be evoked but no awakening)
- As high voltage slow wave activity increases, can result in stage 3 NREM sleep. Lasts for few mins but transitional to stage 4
- Stage 4 involves more high-voltage slow wave activity and a larger stimulus needed for arousal
- REM sleep in first cycle is short-lived and has a variable arousal threshold, selective attention to internal stimuli precedes a response or included in the dream
How does synchronized sleep affect the sleep cycle?
SWS dominates the NREM part of the sleep cycle at the start of the night, as a response to the length of wakefulness before, but diminishes later in the night. REM episodes longest near the end of the night, and brief episodes of wakefulness intrude later in the night
What is the length of sleep?
Lots of variability, can be determined by genetics and staying up late can impact. Length of prior waking can affect how much one sleeps, due to circadian rhythm processes. The amount of REM sleep can increase as the sleep is extended
What are generalizations about sleep in the healthy young adult (this amount of detail not needed)?
- Sleep is entered through NREM sleep.
- NREM sleep and REM sleep alternate with a period near 90 minutes.
- SWS predominates in the first third of the night and is linked to the initiation of sleep and the length of time awake
- REM sleep predominates in the last third of the night and is linked to the circadian rhythm of body temperature.
- Wakefulness in sleep usually accounts for less than 5% of the night.
- Stage 1 sleep generally constitutes about 2% to 5% of sleep.
- Stage 2 sleep generally constitutes about 45% to 55% of sleep.
- Stage 3 sleep generally constitutes about 3% to 8% of sleep.
- Stage 4 sleep generally constitutes about 10% to 15% of sleep.
- NREM sleep, therefore, is usually 75% to 80% of sleep.
- REM sleep is usually 20% to 25% of sleep, occurring in four to six discrete episodes.
How does age affect sleep stage distribution?
- adults have longer cycles than newborns (have around 50/60 mins but up to 90 for adults)
- not fully developed EEG patterns of NREM not present at birth like the ability to support high-voltage slow wave and NREM stages 3 and 4 become prominent
- SWS is maximal in children but decreases with age
-REM sleep as a proportion of total sleep is maintained throughout, with absolute amount of REM linked to intellectual functioning - arousals during sleep increase with age
How does prior sleep history impact sleep distribution?
- sleep loss can result in recovery sleep which is longer and deeper with a higher arousal threshold
- REM shows a rebound on the following nights after an episode of sleep loss
- an irregular sleep schedule or sleep disturbances can result in a strange distribution of sleep states like premature REM like hypnagogic hallucinations, sleep paralysis etc
- lab sleep evaluation linked to more arousals, delayed REM and disruption of normal distribution of REM sleep, skipping of REM sleep
