Sleep
GENERAL
naturally recurring state
characterized by unconsciousness, suspended sensory, inactivity of most voluntary muscles
heightened anabolic state: growth/rejuvenation of immune, nervous, skeletal, muscular systems
observed in all mammals, all birds, and many reptiles, amphibians, and fish
ASSESSMENTS OF SLEEP
commonly assessed by polysomnography in specialized sleep laboratory
EEG of brain waves
electrooculography (EOG) of eye movements
electromyography (EMG) of skeletal muscle activity
STAGES OF SLEEP
in mammals and birds
two broad types: rapid eye movement (REM) and non-rapid eye movement (NREM or non-REM) sleep
each has distinct physiology, neurology, and psychology
American Academy of Sleep Medicine (AASM) divides NREM into three stages: N1, N2, and N3
N3 = delta sleep or slow-wave sleep (SWS)
and then there's REM
sleep cycles through the night
deep sleep early on
more REM toward morning
cycles normally in this order: N1 → N2 → N3 → N2 → REM
humans sleep cycles lasts 90-110 minutes on average
each stage may have a distinct physiological function
sleep may exhibit loss of consciousness but not fulfill its physiological functions
(still feel tired after apparently sufficient sleep)
idea from class: schedule your sleep in 90 minute increments
easier to wake up
NREM
three stages
little dreaming
N1
alpha waves transition from 8-13Hz (awake) to theta waves at 4-7Hz
aka somnolence or drowsy sleep
positive myoclonus (twitching/jerking) may be present
hypnagogic hallucinations may occur
loss of some muscle tone and most conscious awareness wanes
N2
sleep spindles ranging from 11-16 Hz (mc 12-14 Hz) and K-complexes
muscular activity decreases
conscious awareness of external environment disappears
45%-55% of total sleep in adults
N3
deep or slow-wave sleep
minimum of 20% delta waves 0.5-2 Hz, peak-to-peak amplitude >75 μV
(EEG standards define delta waves as 0 - 4 Hz, sleep standards use range of 0.5 - 2 Hz)
parasomnias: night terrors, nocturnal enuresis, sleepwalking, and somniloquy occur
old: N3 = 20%-50% delta waves, stage N4 = 50%+ delta waves (these now combined)
REM sleep
rapid eye movement sleep
20%-25% of total in most adults
rapid eye movements
rapid low-voltage EEG
memorable dreaming
descending muscular atonia: paralysis of muscles may protect us from self harm during dreams
HISTORY
first described in 1937 by Alfred Lee Loomis et al
differentiated via electroencephalography (EEG)
five levels (A to E) representing the spectrum from wakefulness to deep sleep
1953 REM sleep discovered as distinct
William Dement and Nathaniel Kleitman reclassified sleep into four NREM stages and REM
1968 staging criteria standardized by Allan Rechtschaffen and Anthony Kales
"R&K sleep scoring manual."
NREM sleep in four stages
slow-wave sleep comprising stages 3 and 4
stage 3: delta waves made up less than 50% of the total wave patterns
stage 4: more than 50% in stage 4
stage 5: REM sleep
2004 AASM commissioned AASM Visual Scoring Task Force to review the R&K scoring system
review-->several changes
most sig: combination of stages 3 and 4 into Stage N3
revised scoring published in 2007 as:
The AASM Manual for the Scoring of Sleep and Associated Events
arousals and respiratory, cardiac, and movement events were also added
TIMING OF SLEEP
controlled by circadian clock, sleep-wake homeostasis, and in humans, willed behavior
circadian clock-->temp fluctuations
adenosine = neurotransmitter that inhibits many bodily processes assoc w wakefulness
adenosine created during day, high levels-->sleepiness
(I recall that recent studies of acupuncture show that needles cause local adenosine increases)
in diurnal animals sleepiness = melatonin release and body temp decrease
chronotype = the circadian rhythm determining ideal timing restorative sleep episode
SLEEP DEBT AND NORMAL WAKING TIMES
homeostatic sleep propensity
= need for sleep as a fx of time elapsed since last adequate sleep episode
sleep offset = awakening: primarily determined by circadian rhythm
**person who regularly awakens at an early hour will usu not be able to sleep much later than normal waking time, even if moderately sleep-deprived
GENETICS
sleep duration affected by gene DEC2
people with a mutation of this gene sleep two hours less than normal
neurology professor Ying-Hui Fu et al bred mice w the DEC2 mutation
OPTIMAL AMOUNT OF SLEEP
meaningful when timing is in relation to circadian rhythms
**major sleep episode mb inefficient/inadequate when it occurs at "wrong" time of day
one should be asleep at least six hours before the lowest body temperature
**timing is correct when two circadian markers occur after the middle of the sleep episode and before awakening:
1) maximum concentration of the hormone melatonin
2) minimum core body temperature
considered to be adequate when: no daytime sleepiness or dysfunction
SLEEP MISPERCEPTION
self-reported sleep duration is only moderately correlated with actual sleep time
**those affected with sleep state misperception may typically report having slept only four hours despite having slept a full eight hours
STUDY
U. Ca. San Diego psychiatry study
n = over one million adults
people who live the longest self-report sleeping 6-7 hours/night
ANOTHER STUDY
sleep duration and mortality risk in women
similar results
"sleeping more than 7-8 hours per day has been consistently associated with incr mortality" cause mbdt depression, socioeconomic status
lower sleep hours-->reduced morbidity only in those who wake naturally after less sleep
may not apply in those who use an alarm
EFFECTS OF DEPRIVATION
impairment of normal maintenance by sleep
more than double the risk of death from cardiovascular disease
**too much sleep can also be assoc with 2X risk of death, but not dt CV causes
weight gain, hypertension
Type 2 diabetes
incr cort-->incr somatostatin-->decr GH and melatonin
ASSOCIATIONS WITH TROUBLED SLEEP
psychiatric disorders: depression, alcoholism, bipolar disorder
up to 90% of adults with depression have sleep difficulties
incl disturbances in continuity, decreased delta sleep, altered REM patterns
AGE
children need more
up to 18 hours for newborn babies
newborn spends almost 9 hours a day in REM sleep
age five ish: slightly over two hours is spent in REM
1-12 months 14-18 hours
1-3 years 12-15 hours
3-5 years 11-13 hours
5-12 years 9-11 hours
Adolescents 9-10 hours
Adults, including elderly 7-8(+) hours
Pregnant women 8(+) hours
SLEEP DEBT
the effect of not getting enough rest
large debt causes mental, emotional, physical fatigue
diminished abilities to perform high-level cognitive functions
neurophysiological and functional imaging demonstrate:
**frontal regions of the brain are particularly responsive to homeostatic sleep pressure
no agreement on:
how much sleep debt it is possible to accumulate
whether it is accumulated against an individual's average sleep or some other benchmark
whether the prevalence of sleep debt among adults has changed appreciably
** appears likely that children are sleeping less than previously
PURPOSE AND MECHANISMS
only partially clear
thought to conserve energy, but decreases metabolism only 5-10%
hibernating animals return from hypothermia to euthermy to sleep ("energetically expensive")
FUNCTIONS OF SLEEP
wound healing
immune system (more WBCs)
no proven assoc w/ somatic growth in children
slow-wave sleep (SWS) affects GH levels in adult men
men with a high % SWS (average 24%) had high GH secretion (and inverse for 9% group)
anabolic hormones secreted preferentially during sleep
duration inversely related to animal size and directly related to basal metabolic rate
rats with very high basal metabolic rate sleep for up to 14 hours a day
elephants and giraffes with lower BMRs sleep only 3-4 hours per day
rats kept awake indefinitely develop skin lesions, hyperphagia, loss of body mass, hypothermia, and, eventually, fatal sepsis
ONTOGENESIS HYPOTHESIS OF REM SLEEP
the activity occurring during neonatal REM sleep (or active sleep)
particularly important to the developing organism
(Marks et al., 1995)
deprivation of active sleep early in life-->behavioral problems, permanent sleep disruption, decreased brain mass (Mirmiran et al., 1983), and abn amount of neuronal cell death (Morrissey, Duntley & Anch, 2004)
BABIES REALLY NEED THEIR REM SLEEP
REM sleep appears imp brain development
occupies the majority of time of sleep of infants
among species: the more immature the baby is born, the more time it spends in REM sleep
REM-induced muscle inhibition may allow brain development by activating synapses
REM deprivation results in developmental abnormalities later in life
this does not explain why older adults still need REM sleep
aquatic mammal infants do not have REM sleep in infancy, it incr as they age
MEMORY PROCESSING
working memory affected by sleep deprivation
important because it keeps information active, supports higher-level cognitive functions:
decision making, reasoning, episodic memory
memory affected differently by certain stages of sleep
procedural memory benefits from late, REM-rich sleep
declarative memory benefits from early, SWS-rich sleep
after spatial exploration hippocampal place cells are reactivated during SWS
SWS plays a large role in the consolidation of episodic memories
there is a correlation between sleep and the complex functions of memory
an essential part of memory & learning = nerve cell dendrites' sending of information to the cell body to be organized into new neuronal connections
process demands that no external information is presented to these dendrites
this may be why it is during sleep that memories and knowledge are solidified and organized
PRESERVATION AND PROTECTION THEORY
sleep serves an adaptive function
protects the animal during part of day when being active is risky
(Allison & Cicchetti, 1976; Webb, 1982)
HOWEVER
this theory fails to explain why the brain disengages from the external environment
brain consumes a large proportion of the body's calories
preservation of energy could occur by limiting its sensory inputs
sleep is a "drive"
does not explain why lion sleep so much
does not explain why aquatic mammals sleep while moving
DREAMING
perceived experience of sensory images and sounds during sleep
dreamer usu perceives sequence as participant rather than observer
stimulated by the pons and mostly occurs during the REM phase of sleep
many hypotheses about the functions of dreaming
Freud: dreams are the symbolic expression of frustrated desires in unconscious mind
modern: consolidation & organization of synaptic cnxns formed during learning & experience
activation synthesis theory: random firing of neurons in the cerebral cortex during REM
-->story created by forebrain in attempt to make sense of the nonsensical sensory information
CAUSES OF SLEEP TROUBLE
excessive exposure to bright light within hours of bedtime
resisting the urge to fall asleep
pain, illness, drugs, stress
sleep apneas, narcolepsy, primary insomnia
periodic limb movement disorder (PLMD), restless leg syndrome (RLS)
circadian rhythm sleep disorders)
fatal familial insomnia
age: more easily awakened, less ability to consolidate sleep
stimulant usage
alcohol consumption
late meals
BEFORE ARTIFICIAL LIGHT
prelight cultures have more broken-up sleep patterns
people go to sleep sooner after the sun sets, wake several times throughout the night
sleep punctuated with periods of wakefulness, perhaps lasting several hours
boundaries between sleeping and waking are blurred
NOMADS AND HUNTER GATHERERS
fragmented sleep pattern
people sleep at all times of the day and night for shorter periods
SOURCES
http://en.wikipedia.org/wiki/Sleep