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Sleep Flashcards

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1
Q

Sleep

A
  • A periodic, natural, reversible behavioural state of perceptual disengagement from, and unresponsiveness to the environment (Steinberg, 2007)
  • Different from:
    • hibernation
    • being in a coma → not easily reversible
    • on anesthetic → not easily reversible
  • Role in:
    • Recuperation
    • Growth
    • Mental function
  • Quality and quantity of sleep changes as we get older
  • Stages also change as we age → proportion of REM sleep decreases
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2
Q

Chronotype

A
  • Behavioral manifestation of underlying circadian rhythms of myriad physical processes. A person’s chronotype is the propensity for the individual to sleep at a particular time during a 24-hour period. It determines whether we are a morning person or night owl
  • Determined by genes
  • This can change over the lifespan
  • Social jet lag: more than half of people (in industrialised societies) may have circadian rhythms out of phase with the schedule they keep
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3
Q

Randy Gardner

A
  • Broke world record for longest time awake: 264 hours (1965)
  • After 2 days: irritable, nauseated, memory problems, could not watch TV anymore
  • After 4 days: mild delusions, overwhelming fatigue
  • After 7 days: tremor, language problems, EEG abnormality
  • After end of trial: normalised quickly again (not true for some animals deprived of sleep).
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4
Q

Sleep deprivation

A

Impacts:

  • Mood
  • Cognitive performance
  • Executive attention
  • Working memory
  • Motor function
  • Mental health problems
  • Obesity
  • Deficits accumulate over time (Drumer & Dinges, 2005)
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5
Q

How is sleep measured?

A
  • Polysomnography: recording of multiple signals during sleep
    • EEG: brain activity
    • EMG: muscle activation
    • EOG: eye movements
    • Heart rate
    • Respiration
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6
Q

EEG

A
  • Recordings correspond to summed post-synaptic potentials
  • The highest influence to the EEG signal comes from electric activity of the cortex
  • Two most important factors contributing to EEG signal: cellular organization and synchrony
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7
Q

EEG rhythms during sleep/wakefulness

A
  • Beta /Gamma → awake and alert
  • Alpha → relaxed wakefulness
  • Theta → can occur during sleep and wake
  • Delta → slow and deep sleep
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8
Q

Stages of sleep

A
  • Wakefulness: beta and gamma EEG oscillations
  • NREM (stage 1): alpha waves - higher aplitude, lower frequency
  • NREM (stage 2/3): start seeing sleep spindles (produced by cells in thalamus) and K-complex (produced by the hippocampus)
  • NREM (stage 4): high amplitude, slow oscillations - lots of neurons active at the same rhythm
  • REM stage: EEG similar to wakefulness
  • This cycle is repeated 4-5 times a night, each cycle lasting around 90-110 minutes
  • More NREM sleep at beginning of night, more REM sleep at the end
  • Brain is really active when you are asleep
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9
Q

Hypnogram

A
  • Diagram that shows the transition between the different sleep stages during a night of sleep
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10
Q

Markers of NREM sleep

A
  • Slow oscillations
  • Spindle - thalamus
  • K-complex - hippocampus
  • Ripple - hippocampus
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11
Q

Markers of REM sleep

A

Theta oscillations - particularly prominent in the rodent hippocampus

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12
Q

Characteristics of REM sleep

A
  • REM = Rapid eye movement
  • More likely to remember your dreams during REM phase of sleep
  • Extrastriate visual cortex is in the area of the visual cortex that process external information
  • Areas of the pons were more active during REM sleep → inhibits motor response
  • REM sleep plays a role in inhibiting motor response
  • Body also goes through activity during REM sleep
  • Physiological changes:
    • Eye movements
    • Heart rate increase
    • Respiration rate increase
    • Penile erections
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13
Q

Slow wave vs REM sleep

A
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14
Q

Mechanisms of sleep

A
  • Increase of GABAergic activity in cortex
  • Deactivation of locus coeruleus (noradrenaline)
  • Less activity of reticular activating system
  • Reduced histamine and orexin (hypothalamus)
  • Increase melatonin (pineal gland)
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15
Q

Role of reticular formation in sleep

A
  • Modulatory systems control rhythmic behaviours of thalamus
  • Blocks flow of sensory information up to the cortex
  • Inhibits descending pathways (e.g. motor neurons)
  • Lesion of brain stem → coma
  • Electrical stimulation of midbrain (e.g., reticular formation) → alert
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16
Q

Role of cortisol in sleep

A
  • People who don’t sleep well have raised cortisol (bidirectional cause and effect)
  • Cortisol is raised in older people → worse sleep
  • Cortisol oscillates throughout the day, but peaks just before you wake up
  • It can be raised in anticipation of waking
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17
Q

Role of melatonin in sleep

A
  • Melatonin prepares you for darkness behaviour (in humans, sleep) → peaks at night
  • Made in pineal gland
  • Biological clock (SCN) drives melatonin rhythm
  • Melatonin can help diagnose circadian rhythm disorders
  • Not affected by meals, stress, bathing, sleep
  • Is affected by light. Total blindness associated with sleep disorders
18
Q

Arousal promoting neurotransmitters/hormones

A
  • Noradrenaline
  • Serotonin
  • Acetylcholine
  • Histamine
  • Hypocretin (hypothalamus) → excites all other systems (loss → narcolepsy)
19
Q

Sleep promoting hormones/neurotransmitters

A
  • GABA
  • Some ACh neurons fire to induce REM – produces eye activity
    • Adenosine
  • Dopamine: modules REM sleep, contributes to dream generation (internal, exploratory environment)
20
Q

Dual process model of sleep

A
  1. Sleep-wake Homeostasis, or Process S, is the accumulation of sleep-inducing substances in the brain. It’s an internal biochemical system that operates like a timer, generating homeostatic sleep drive or the need to sleep after a certain amount of time awake. It effectively reminds the body that it needs to sleep - so the longer you’ve been awake, the stronger your desire for sleep becomes.
  2. The circadian process, also known as Process C, is the regulation of the body’s internal biological processes and alertness levels. This is what controls the timing of sleep and it coordinates the light-dark cycle of day and night. Your circadian rhythm is what regulates your body’s sleep patterns, feeding patterns, core body temperature, brain wave activity, and hormone production over a 24-hour period.

To break it down simply, the first process causes a pressure to fall asleep, whilst the second dictates the daily rhythm of sleep.

21
Q

Circadian rhythms

A
  • Even plants have circadian rhythms e.g. plants close up in the night and open at night.
  • External cues: zeitgebers e.g. seasons, light
  • Deep cave study
    • Wake/sleep, lights on/off, eating → all whenever they like
    • Initially day was 25 hours, then it rose to 30-36 hours (stay awake 20 hours, sleep 12 hours)
    • Desynchronised: sleep and body temperature
    • Lots of confounds with this study
      • More recent studies have put people in a room (not allowed to switch light off), only snack allowed → human rhythm was demonstrated to be 24h long
22
Q

Biological clock

A
  • SCN (suprachiasmatic nuclei) within hypothalamus
  • Receives input from the retina → light sensitive ganglion cells
  • Ganglion cells:
    • large, nonselective receptive fields responding to luminance
    • Not rods or cones → new photoreceptor that’s slowly excited by light → signal to SCN
    • Photosensitive retinal ganglion cells or melanopsin-containing retinal ganglion cells
  • SCN lesions in squirrel monkeys cause an irregular sleep-wake cycle
23
Q

Jet lag

A
  • Mismatch between internal and external clocks
  • Adjusting eastwards is harder as our clock is slightly more than 24 hours
  • Consequences:
    • Elevates cortisol
    • Sleepless/ fatigue (melatonin disruption)
    • Loss of concentration
    • Change in appetite (ghrelin)
    • Body temperature fluctuations
  • Best way to combat it:
    • Restrict light exposure/ meals/ activity
    • Can take a supplement of melatonin
24
Q

Main sleep disorders

A
  • Insomnias (difficulty going to sleep/ staying asleep)
  • Hypersomnolence (daytime sleeping e.g., narcolepsy)
  • Parasomnias (disorders that disrupt sleep – e.g., sleepwalking)
  • Circadian rhythm disorders (timing of sleep)
  • Breathing disorders (E.g., sleep apnea)
25
Q

Insomnia

A
  • Disorder not due to a substance or known physiological condition
  • 30% of population report one or more of the symptoms of insomnia but only 10% fulfil diagnostic criteria
  • Causes:
    • Overactive thyroid
    • Mental or physical health
    • Medication
    • Stress
    • Environmental factors
26
Q

Parasomnia

A
  • Group of sleep disorders that involve unwanted events or experiences that occur while you are falling asleep, sleeping or waking up
  • May include abnormal movements, behaviours, emotions, perceptions or dreams
  • You remain asleep during the event and often have no memory that it occurred
    • Sleep walking
    • Night terrors
    • Restless leg syndrome
    • Periodic limb movements
    • Sexsomnia
    • Sleep-related eating disorder
    • REM sleep behaviour disorder
27
Q

REM sleep behaviour disorder

A
  • Sleep paralysis is absent
  • Most patients are male
  • Descending activity from brain to muscles usually blocked by pons
  • Pons lesioned → REM behaviour disorder
  • Can also be related to some other conditions (e.g., Parkinson’s)
  • Treatment: benzodiazepines or melatonin
28
Q

Sleep apnea

A
  • Muscles and soft tissues in the throat relax and collapse sufficiently to cause a blockage of the airway
  • Oxygen level in your blood drops
  • Brain disturbs sleeps → waken to resume breathing
  • Often don’t remember awakenings
  • Causes:
    • Commonly associated with weight
    • Lifestyle: alcohol, smoking, medicines
    • Having a large neck/ unusual neck structure
    • Correlation with: Gender (male), Age (40+), Menopause
29
Q

Circadian rhythm disorders

A
  • Different from voluntary or imposed shift in timing of sleep (e.g., shift work; jet lag)
  • Seen in blind people, also co-morbid with ADHD, depression or neurodegenerative disease
  • Altered or disrupted sensitivity to external cues
    • Delayed sleep phase disorder
    • Advanced sleep phase disorder
  • Difficultly in diagnosable disorder vs. subclinical tendencies
  • Individual differences in tolerance of disparities in circadian synchronisation
  • Treatment involves light exposure/ melatonin
30
Q

Narcolepsy

A
  • Narcolepsy is a long-term neurological disorder that involves a decreased ability to regulate sleep-wake cycles.
  • Symptoms often include periods of excessive daytime sleepiness and brief involuntary sleep episodes.
  • About 70% of those affected also experience episodes of sudden loss of muscle strength, known as cataplexy.
  • Caused by significantly less hypocretin than normal (Thannickal et al., 2000)
31
Q

Why do we dream?

A
  1. Wish fulfilment (Freud)
    • Unconscious way to express sexual and aggressive fantasies
  2. Physiological function theory: promote neural development and preserve neural pathways by providing the brain with stimulation
  3. Activation – Synthesis Model (Hobson & McCarley)
  • Dreams are products of brain neuron activity in the visual cortex, memory areas, and emotion areas.
  • No external stimulus; so brain tries to make sense of neuron activity = content of a “dream”
  • Explains randomness of dreams
  • Prefrontal cortex shuts down during REM so you have fewer inhibitions and don’t question illogical parts of dreams
32
Q

Why do we sleep?

A
  • Restoration (Moruzzi, 1972; Vyazovskiy & Harris, 2013)
    • Clearance of toxic waste products twice as fast during sleep than wake (Xie et al., 2013)
    • Slow oscillations à short period of rest for all neurons
  • Adaptation (keep us out of trouble! – Meddis, 1975; Seigel, 2009)
    • Sleep follows our biology: we don’t see well at night, we are most vulnerable at night
    • Saves energy
    • Allows awakening when needed
  • Cognitively beneficial (Walker, 2009) e.g., emotion regulation
    • Strips memories of emotional tone, non-emotional aspects are strengthened
  • Retention and consolidation of learnt material (e.g., Born, Stickgold, etc.)
33
Q

Hippocampus activity during sleep

A
  • Place cells in the hippocampus code spatial relations
  • Place cells are activated in the same order during sleep as during exploring a maze
  • Rats “dream” running through the maze
34
Q

Types of memory

A
  • Declarative memory: factual informaiton recall e.g. capitals
  • Procedural memory: learning motor sequences e.g. how to ride a bike
35
Q

Ebbinghaus & Forgetting

A
  • Experiment demonstrating link between sleep and learning
  • Learning and forgetting nonsense syllables
  • After a certain time, forgetfullness would stabilise. This would be after sleep. So sleep helps us to stop forgetfulness
36
Q

Partial sleep deprivation study

A
  • Plihal & Born, 1997
  • Used standard procedural and declarative memory tasks: mirror tracing and paired associate learning
  • Exploited the fact that early sleep is SWS-rich, and late sleep is REM-rich
  • 4 groups (sleep/wake), early/late retention interval
  • For early retention interval, sleep benefits declarative but not procedural memory (SWS?)
  • For late retention interval, sleep benefits procedural but not declarative memory (REM?)
37
Q

Targeted memory reactivation

A
  • Rudoy et al., 2009
  • Participants had to learn 50 object locations on a board and an auditory cue would be played at the same time
  • They would then have a nap and half of the participants would hear the cue in their sleep and some did not
  • The change in spatial recall was significantly stronger for the cued participants
38
Q

Rasch et al., 2007

A
  • Presentation of a cue (odour) associated with memory trace during SWS increased consolidation of this memory content
  • This didn’t work during REM
  • Also didn’t generalise to procedural memory
  • fMRI scans showed that the hippocampus would activate more during sleep to the odours that had been presented while awake
39
Q

Is it good to nap?

A
  • Mednick et al., 2003
  • Short naps improve performance
  • BUT ONLY, if REM-sleep was present
  • similar effects of a short nap and a whole night‘s sleep
40
Q

Wakeful rest

A
  • Dewar et al., 2012
  • Story learning task
  • Taking a break and doing nothing was shown to improve recall even a week later
  • Limitation: wakeful rest and sleeping isn’t the same → lots of confounds
41
Q

Vocabulary learning and sleep

A
  • Gais et. al, 2006
  • Vocabulary (German) learning and sleep study
  • Time of learning impacted the forgetting % - students seem to remember better when they learn in the evening
  • Sleep deprivation increased the forgetting %

Brain and Behaviour (17 decks)

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