Week 6: Sleep
Biorhythms
Circadian
Ultradian
repeating 24 hour cycles
regular 90-120 min cycles of activation and quiet
seen in REM and in brain activity during wakefulness
tied to sleep-wake cycles
Zeitgebers
time givers
Light ☀
entrain internal biological clocks to 24-hour cycle of earth rotation
Free-running circadian rhythms
24.2 to 24.9 hours
occur in absence of light and causes severe sleep disruptions
Relation to Food 🍖
⬆ effective when there is enough food
⬇ effective when there is food shortage
Chronotypes
individual differences in circadian patterns
Lark, night owl, in-between
many switch to owl chronotype in teens
dramatic drop in melatonin on onset of puberty
revert back after puberty possibly due to maturation of sleep regulation brain regions
Disruptions
Shift Maladaptation Syndrome
Jet Lag
Demographic
Symptoms
excessive sleepiness at work,
impaired sleep at home
health, personality, mood and interpersonal problems
affects middle-aged and older workers the most
experienced by individuals working evening or night shifts
affects larks more than night owls
Work impactss
nurses on night shift make 30% more errors
higher accident rates in night shifts
arises from crossing time zones
Symptoms
Irritability 😠
Sleepiness 💤
Chronic Jet Lag
flight attendants that crossed time zones weekly for 4 or more yrs
⬇ Reaction Time
9% more mistakes
Temporal lobe atrophy without sufficient recovery time
easier to adjust to phase-delays than phase-advances
Phase-Delays
travelling West
later shifts than usual
Phase-Advances
travelling East
earlier shifts than usual
Daylight Savings Time
shift clock 1 hour back in fall 🍁 (phase-delay)
shift clock 1 hour forward in spring 🍀 (phase-advance)
produces jet lag symptoms for a few days
associated with cardiovascular disease
sleep deprivation leading to ⬆ SNS activation and
⬆ inflammation
Biology
Superchiasmatic Nucleus
name from its location above (supra) the optic chiasm
receives input from the axons of
Intrinsically photosensitive retinal ganglion cells (ipRGC)
contain a photopigment called melanopsin
forms the retinohypothalamic pathway from the retina to the SCN
Functions
distinguishes between day and night and is most active in day
regardless of activity patterns
cathemeral (☀ and 🌙)
SCN activity generates SNS response
SNS response affects amount of melatonin synthesised by pineal gland
⬇ SNS activity leads to ⬇ melatonin made
⬆ SNS activity leads to ⬆ melatonin made
crepuscular
(active in twilight)
master clock that coordinates peripheral clock activity
maintains circadian rhythms independently
isolated SCN tissue cultures have brain activity fluctuations that match source animal circadian rhythms
Hamsters exhibit cycle length of transplanted SCN
Rat experiments
SCN cells adjust in 1 to 2 cycles
Lung and muscle tissues require 6 cycles
Liver tissues require more than 16 cycles
Astrocytes
most active at 🌙
finely tunes SCN circadian activity
disabling astrocytes leads to slight lengthening of circadian rhythms
Cellular Basis
fruit fly research
Period Gene
Timeless Gene
releases mRNA into the cytoplasm to produce PER proteins
produces TIM proteins
TIMs bind with PERs to form a PER/TIM complex
PER/TIM complex can enter nucleus and inhibit period gene
PER proteins ⬆ at 🌙 and ⬇ in the ☀
Melatonin
released from pineal gland into CSF in the third ventricle
release is suppressed by light
levels increase 2 hours before sleep and drop over the night
Supplementation
helpful in regulating sleep patterns for individuals with visual impairments
has antioxidant properties
can potentially improve symptoms in neurodegenerative disorders such as Alzheimer's
melatonin receptors in cells are involved in immune system
potentially improve immune function
Cortisol
📈 in the morning and 📉 at night
released during stress
stress-induced cortisol associated with poor sleep quality
associated with jet lag effects
flight crew that cross over 8 time zones have 33% more cortisol in saliva than ground crew
Functions
mobilise energy stores
higher heart rate
higher blood pressure
Growth Hormone
Release
Functions
stimulates physical growth in children
building muscle and bone mass
maintaining immune system function
released during Stage 3 of nREM sleep
peaks during puberty onset and drops after 21
reduced by sleep deprivation
EEG Research
Alertness 😮
associated with desynchronous activity (alternating beta and alpha activity)
Beta Waves
Alpha Waves
associated with high alertness and active information processing
rapid waves of 14 to 30 Hz
highly irregular and low amplitude
slightly slower than beta waves with 8 to 13 Hz
more regular and larger amplitude
Mu Waves
frequency overlaps with alpha at 9 to 11 Hz
localised in the motor cortex
advances in EEG may allow researchers to measure gamma-band activity
more than 30 cycles per second
prominent in the front of the brain
prominent in the back of the brain (visual cortex)
observed at rest but suppressed by movement
associated with relaxation
closing eyes can initiate alpha wave activity
obvious during sensory and visual processing
Sleep 😴
Stage 1 NREM
alpha waves replaced by theta wave activity
⬇ in heart rate and muscle tension
Emergence of sleep myoclonia
Stage 2 NREM
Sleep spindles
produced by interactions between the thalamus and cortex
12 to 14 Hz
last around 0.5 seconds
K complexes
made of single delta waves
occur randomly or in response to unexpected stimuli (eg. loud noises)
accounts for 50% of sleep
Stage 3 NREM
features delta wave activity (1 to 4 Hz)
Brain energy usage decreases to 11% to 40% of waking brain
PNS activity lowers blood pressure, heart rate, breathing, body temperature
Sharp-wave ripples
occur in the hippocampus
rapid bursts of waveforms
REM
vivid dreaming
features waking beta activity and theta activity in the hippocampus
brain energy usage increases to or beyond wakefulness levels
SNS activation
increase in blood pressure, breathing and heart rate
increased blood flow in genital areas
major postural muscles are immobilised while smaller muscles can still twitch
Patterns
1st 4 hours
longer periods of NREM and short REM periods
Stage 3 NREM is dominant
Next 4 hours
REM is dominant stage
Any NREM will be in Stages 1 to 2
Stage 3 NREM infrequent or absent
behaviours that occur at regular intervals in response to internal, biological clocks
Networks
Waking
Ventral Pathway
Dorsal Pathway
Medulla ➡ Hypothalamus ➡ basal forebrain
Cholinergic
mesopontine nuclei
found in midbrain reticular formation
secrete acetylcholine
found in junction of the pons (pontine) and midbrain (meso)
Locus Coeruleus
Anterior Raphe Nuclei
important in managing sleep-wake cycles
communicates with preoptic area, SCN and cerebral cortex
secretes most of the brain's norepinephrine
has connections to the thalamus, hippocampus and cortex
communicates with thalamus which moderates cerebral cortex activity and amount of sensory input received
⬆ activity with alertness
⬆ activity with alertness
Default Mode Network
consists of the medial prefrontal, medial parietal, lateral parietal, lateral temporal
Functions
mind wandering
recalling personally relevant memories
planning future events
thinking about beliefs, intentions and motivations of others
overlap of DMN structures with those involved in social behaviour
DMN connectivity
useful predictor of cognitive function
peaks in adulthood and is lower in childhood and older age
unusual DMN activity implicated in neurodegenerative and psychological disorders
Sharing or understanding personal stories and experiencing fictional situations
Integrating internal thoughts and external stimuli to establish a context for understanding situations
NREM Sleep
Preoptic Area (POA)
Functions
aka NREM-on cells
stimulation ⚡ of POA cells produces immediate NREM sleep
lesions result in insomnia
⬇ activity during waking and REM
manage homeostatic control of wakefulness
inhibits waking pathways
Thalamus
synchronises cortical neuron activity in absence of waking circuit activity
electrical stimulation in waking animals produces NREM sleep
DMN
decoupling of anterior parts from posterior parts
possibly associated with reduced consciousness during deep sleep
REM Sleep
CMN
high levels of activity during REM and waking
electrical stimulation produces desynchronous activity
due to connections with thalamus and cortex
REM-on
Rostral Pontine Reticular Formation
found in the pons
lesions in the area inhibit REM sleep
active during REM while inactive in waking and REM
REM-off
Locus Coeruleus
Raphe Nuclei
reduction in REM-off area activity permits REM-on area activity
allows REM to occur
REM-off areas reactivate after 30min of REM, inhibiting REM-on areas
PGO waves
1⃣ PRF stimulates superior colliculi, which communicates with different area of PRF
Responsible for coordinating eye movement timing and direction
2⃣ Lateral Geniculate nucleus is activated
visual centre of the thalamus
3⃣ Occipital lobe
is activated
visual experiences are triggered
location of the primary visual cortex
Muscular Paralysis
Inhibitory signals from PRF ➡ medulla ➡ spinal cord motor systems
rapid eye movements
only occur during 14%-27% of REM
experienced by people with congenital blindness
fingers twitching indicates muscular inhibition stronger at beginning of REM and gradually decreases
Others
⬆ activity in
V2 (secondary visual cortex)
Hippocampus
⬇ activity in
Limbic System
frontal lobe
parietal lobe
DMN
suggests REM significance in memory consolidation
underlie emotional content of dreams
possible reason for illogical nature of dreams
basis for self-referential aspect of dreams
lower DMN activity associated with rapid eye movements
associated with rapid eye movements
Biological Correlates
Alertness
Glutamate
Acetylcholine
⬆ in waking and REM sleep but ⬇ in NREM sleep
⬆ in waking and REM sleep but ⬇ in NREM sleep
Histamines
major neurochemical used by neurons in the thalamus and the hypothalamus
⬆ activity in waking and ⬇ in NREM and REM sleep
neuron activity associated with alertness
Antihistamines
Traditional ones produce drowsiness 😪
Modern ones do not cross blood-brain barrier and do not induce drowsiness
Caffeine ☕
blocks adenosine receptors
REM-off areas
Norepinephrine produced by locus coeruleus
Serotonin produced by raphe nuclei
antidepressant drugs boost both and thus suppress REM
Highest in wakefulness and lowest in REM
promotes alertness
Drowsiness
Adenosine
⬆ throughout the day and until sleep occurs and ⬇ during sleep
prevents secretion of neurochemicals associated with waking
eg. ACh, norepinephrine, serotonin
released by pons and basal forebrain
ATP byproduct that inhibits many brain systems
cholinergic agonists ⬆ mental awareness
Eg. nicotine 🚬
possibly promotes REM-on processes