Biology of sleep Flashcards
Sleep and wake areas in the brain
Anterior hypothalamus - sleep area
Posterior hypothalamus - wake area
- discovered via damage caused by encephalitis
- confirmed with animal lesion studies (Saper et al., 2001)
Reticular formation
- in the brain stem
- Stimulation wakes the person/animal (Mouzzi & Morgan, 1949)
- Ascending reticular activating system originates in the brain stem, keeps us awake
Sleep-wake cycle
Suprachiasmatic nucleus
- gets info directly from the eyes about light levels
- sets sleep-wake rhythm with light
Zeitgebers
- environmental factors that influence the sleep wake cycle
- e.g. light, food/drink, social interaction
Free-running
- 24.2hr circadian rhythm loses synchronicity with 24hr external clock without zeitgebers like light
- Sleep period shifts later each day
Actigraphy
Measures movement with accelerometer
Also measures lights - helps diagnosis of sleep rhythm disorders
Issues with actigraphy
Not a true measure of sleep - poor sleep = less accurate actigraphy. Could be lying still while awake/moving in sleep
Vandenberg et al., 2008
- Ps aged 57-97
- 34% had different TST in sleep diary and actigraphy
Validity of actigraphy
Sadeh 2011
- can provide meaningful data in assessment of insomnia
- useful to assess clinical interviews as well
- 5 day collection recommended
Nightcap/REMview
Electrodes on eyes and forehead - physically measures eye and head movement
- eyes and head moving = wake
- eyes and head still = NREM
- eyes moving and head still = REM
Cantero et al., 2002
Kaji et al., 1994
Sleep depth
Non-mammalian animals have light and deep sleep stages
Sleep depth in mammals is harder to define bc activities don’t increase/decrease in unison:
- NREM looks lighter
- report being in lighter sleep when woken from NREM than REM
- more galvanic skin activity - emotional arousal
- muscle tone maintained
- temp regulation maintained
- REM looks lighter
- greater activity in occipital cortex
- brain temp increases
- cerebral blood flow increases from NREM to REM
- heart rate, respiration rate, blood pressure more variable than in NREM
- EEG resembles wakefulness
- Takahara 2007 - instruction to pay attention to external stimuli during REM influenced late positive potentials or ERP - voluntary attention during REM!
Species differ on how loud a sounds needs to be to wake from NREM or REM
Development of sleep stages
Roffwarg 1966
- More REM in foetus’, newborns, infants
- REM diminishes with age
- TST drops from ~16hrs for newborns to ~6hrs for elderly, bus NREM stays roughly the same
- REM for development? Ensure brain is more active during infancy to aid CNS development
Mortality and sleep length
Ferrie et al., 2007
- too little sleep (6-8 hrs) leads to increased cardiovascular mortality
Patel et al., 2006
- long sleep and mortality mediated by depression and low SES
Default network
Interconnected cortical regions that are active when we aren’t responding to the external environment e.g. daydreaming (Raichle et al., 2001)
Active during sleep
neurochemicals in sleep
Acetylcholine
- originating in brainstem
- promotes high frequency brainwaves in wake and REM
Serotonin
- promotes quiet waking state, reduced cortical activity
- inhibits NREM and REM
- involved in stress response - may account for aspects of stress-related sleep disorders
Noradrenaline
- part of central fight/flight response
- excited neurons of the ARAS
hypocretin
- consolidates wakefulness (increases duration of wakefulness), suppresses REM and enhances wakefulness during starvation
- deficits in narcolepsy
Sleep and body temperature
NREM maintains hypothermy (warm bloodedness)
REM is poikilothermic - body temp follows temp of the room
Suggests NREM evolved more recently than REM
Evolutionary view of sleep stages
Siegel et al., 1998
- monotremes (early mammals e.g. duck-billed platypus) and birds have REM sleep
- Concluded that REM was present in reptiles that evolved into birds and mammals
- SWS evolved later in mammals
Theories for the functionality of REM sleep
Jouvet
- practicing/simulating what your species is good at
Ephron & Carrington
- REM periodically wakes the brain during deep sleep bc brain needs to be occasionally stimulated
Snyder 1966
- sentinel state where we briefly wake to assess surroundings
Siegel 2005
Sleep deprivation in rats and flies causes death quicker than food deprivation
NREM generated by forebrain. Cells in preoptic and basal borebrain cause sleep when stimulated, damage reduces sleep.
Sleep of terrestrial mammals
Amount of sleep differs between mammals
- bats sleep 18-20hrs per day
- elephants and giraffes sleep 3-4hrs per day
Differences not related to body size/temperature
- carnivores sleep more than omnivores sleep more than herbivores
- grazing animals need to eat more, are more susceptible to predators
- Small animals have shorter sleep cycles - may be inertial - time needed to alter brain chemistry, time needed to complete biochemical tasks
Sleep of marine mammals
Cetaceans have uilateral slow waves, no REM
- maintain some awareness of surroundings? Awareness of predators
- Newborn cetaceans are constantly moving, perhaps to keep body temp up bc lack of insulating blubber. Adults are rarely still.
Fur seals have unilateral NREM in water, bilateral NREM and REM on land
NREM and REM functions
NREM
- Neocortical maintenance & recuperation
- Energy conservation
REM
- Memory consolidation
- Development
- Monoamine regulation
NREM functions
Neocortical maintenance and recuperation
Neocortical size doesn’t correlate positively with sleep amount
Elephant has largest neocortex of any terrestrial mammals but one of the smallest sleep periods, rats and platypus have smooth cortices but large amounts of sleep
NREM functions
Energy conservation
Small mammals have large area to mass ratio, therefore may sleep to conserve energy which is quickly lost while awake
Also may be important in newborns
REM functions
Development
Mammals born immature at birth (altricial) have more REM than those born more developed (precocious)
Atricial ammals continue to have more REM while adults
REM functions
Mooamine regulation
Reduced sensitivity and production of neurochemicals (NA, 5-HT, histamine, hypocretin) during REM to regulate levels
REM deprivation acts as an antidepressant - maintains higher levels
Sleep and grey matter volume
Weber et al., 2013
- Sleeping in excess of subjective minimal need is associated with greater grey matter vol. in the medial prefrontal cortex
- vol. in this area correlates with emotional intelligence and lower psychopathy scores in the same participants
Function of sleep: Metabolic clearance
Xie et al., 2013
- Lymph vessels in rest of body remove toxins from tissues
- Glymphatic system in the brain
- Interstitial space increases 60% during NREM
- Floods with CSF and proteins break down toxins
- beta-amyloid cleared 2x faster in asleep than awake mice
- adrenergic receptor antagonists increase interstitial space like in sleep
- buildup of neurotoxins during wakefulness can cause irreversable damage so the homeostatic drive to sleep prevents this - sleep is restorative
I sleep essential?
Cirelli & Tononi 2008
Concluded that YES sleep is essential because:
- all animals sleep
- flies’ sleep pattern change with the life span
- undergo changes in gene expression and electrical activity between sleep and wakefulness similar to mammals
- Sleep is homeostatically regulated in all animal species that have been studied so far
- Lack of sleep can be lethal, cause intrusion of sleep into wakefulness and cause cognitive impairment
