Sleep Flashcards
What does an EEG measure?
changes in electrical activity of different locations in the cerebral cortex’s
Why are EEGs used?
simple and non-invasive
used for research and in clinical settings to diagnose
What determines the amplitude of an ECG wave?
the synchronicity of the neurons firing
more inputs firing in a narrow time window the pyramidal cells response will be synchronized resulting in a larger EMG amplitude (stronger)
Where does the EMG signal originate from?
**voltage difference in synaptic inputs in the apical dendrites from pyramidal cells **
active synpase on the dendrite causes the afferent axon to fire, presynaptic terminal releases glutamate which opens the cation channel -> positivge current flows inot dendrite = slightly negative ECF
current spreads deeper leaviing the fluid slightly positive
EEG electrode measues this pattern
What is the relationship between frequency and amplitude of EEG rythyms?
low frequency + high amplitude = deep sleep/coma
high frequency + low amplitude = alert/awake
What are delta rhythms?
<4 Hz large in amplitude
a hallmark of deep sleep
What are theta rhythms?
4-7 Hz both sleeping and waking states
What are alpha rhythms?
8-12 Hz associated with quiet,waking states
What are gamma rhythms?
30-90 Hz
signal an activated or attentive cortex
What are spindles?
brief 12-14 Hz waves
associated with sleep
What are ripples?
brief bouts of 80-200 Hz oscillations
What was found when measuring EEGs in different mammals?
characteristics are similar across mammals despite large differences in brain mass
What are the two ways synchronous rhythms can be generated?
- central neuronal pacemaker setting the rhythm
- timing arises from collective behaviour of a network of neurons
What is a two neuron oscillator?
one excitatory cell and one inhibitory cells synapse on eachother
with a constant excitatory drive onto the E cell, activity will trade back and forth between the two neurons -> generate a pattern of firing
What is a one neuron oscillator?
thalamic neurons fire in rythmic patterns that do not affect their input
a short pulse of stimulus applied results in rythmic firing first with bursts and then single spikes
Why can the thalamus maintain rythmic firing on its own?
its particular set of voltage gates channels
What drives the rythyms in the cerbral cortex?
the thalamas
thalamic neurons
How do thalamic neurons synchronize with the cortex neurons?
thalamic neurons synapse on cortical neurons which also synapse back onto the thalamic neurons (excitatory)
inhibitory thalamic neurons force neurons to conform to the group to create synchronicity
What doe quiet and whisking states in mice correspond to in regards to synchronicity?
synchronized during quiet states (no information processing)
unsynchronized during whisking states (information processing)
What is the behavioural definition of sleep?
sleep is a readily reversible state of reduces responsiveness to, and interaction with, the environement
What are the stages of sleep?
waking
stage 1
stage 2
stage 3 (slow wave sleep)
REM sleep
What are characteristics of waking?
an alert awake humans EEG is desynchronized
mix of high frequencies with low amplitude
beta activity
What are characteristics of stage 1 of sleep?
alpha rhythms appear during relaxation
sharp waves calles vertex spikes appear
lower amplitude, decreased HR muscle tension
slow eye rolls
afew minutes
What are characteristics of stage 2 of sleep?
brief peridos of sleep spindles and K complexes
What are characteristics of stage 3 of sleep?
large slow delta waves
deepest level of sleep
thalamas dominates = synchronizes large waves
What are characteristics of REM sleep?
deep muscle relaxation
EEG activity similar to waking waking
rapid eye movements (saccades)
What stages of sleep are NREM?
Waking
Stage 1
Stage 2
Stage 3 (SWS)
How is NREM sleep characterized?
slow rolling eye movements (stage 1) followed by decreases in muscle tone, body movements, heart rate, breathing, blood pressure, metabolic rate, and temperature
all parameters reach their lowest during SWS (stage 3) sleep
How is REM sleep characterized?
rapid ballistic eye movementrs as well as by pupillary constriction, paralysis of many large muscle groups, and the twitching of smaller muscles in the fingers, toes and middle ear
blood pressure, heart rate, and metabolism increase to levels almost as high as in awake state
What is the sleep cycle?
start with transition fromm awake to stage 1then progress through deeper stages of NREM sleep then into REM sleep
repeated seversl times (~100 mins) but each cycle has shorter shallower NREM periods and longer REM periods
How do sleep patterns change with age?
With increasing age the amount of total sleep and REM sleep decreases
What are characteristics of infants sleep patterns?
stable patterns don’t appear until about 16 weeks
they can move into REM sleep from awake
Large amount of REM sleep and total sleep
What are characteristics of elderly sleep patterns?
can fall asleep but not stay asleep
frequent awakenings
severe reduction in stage 3 sleep -> diminishes cogntive abilty
What are consequences of 2-3 weeks of sleep deprivation in animals?
loss of weight
fail to control body temperature
develop infections
eventually death
What is fatal familial insomnia?
an inherited genetic disorder in humans that causes someone to stop sleeping midlife and die 7-14 months later
- normal sleeping patterns until this point
develop large holes in the frontal cortex
- hallucinations, seizures, loss of motor control
What occurs during hibernation that shows the important of sleep?
euthermic arousals
spikes in body temperature to normal values where animals display slow-wave sleep
What is unihemispheric sleep?
one hemisphere can exhibit the ECG signs of wakefulness while the other shows characteristics of sleep
- alternate which sleep
- dolphins
- ducks
- birds
When do humans exhibit unihemispheric sleep?
associated with the first-night effect - first night sleep in an unfamiliar place
- one hemisphere is kept partially more vigilant than the other as “night watch,” which wakes the sleeper up when unfamiliar external signals are detected
Define memory
the ability to retain information, based on the mental process of learning or encoding, retention across some interval of time, and retrieval or reactivation of the information
Define episodic memory
the memory of a particular incident or a particular time and place. comprises associations of several elements such as objects, space, and times. the associations are encoded by chemical and physical changes in neurons as well as by modifications to synapses between neurons
Define memory consolidation
a process that converts and stabilizes information from STM into long-term storage. hippocampal-neocortical memory consolidation involves the transfer of hippocampal episodic memory into the neocortex during offline (such as sleep) process after waking experiences in memory acquisition
*NREM sleep
Define encoding
a stage of memory formation in which the information entering sensory channels is passed into STM
Define engram
the physical basis of a memory in which the information entering sensory channels is passed into STM
How is memory consolidated?
synaptic changes in the hippocampus initiate memory formation
the hippocampal neurons interact with neurons in areas of the neocortex
a temporary memory trace (STM) is formed in the hippocampus through synaptic consolidation, and engrams later develop in the neocortex through system consolidation
* over time, memory depends more on connections in the neocortex and less on the hippocampus (retrieval)
What is a cognitive map?
a mental representation of a spatial relationship
What are place cells?
a neuron within the hippocampus that selectively fires when the animal is in a particular location
What are grid cells?
a neuron that selectively fires when an animal crosses the intersection points of an abstract grip map of the local environment
Explain the interaction between inputs and synaptic matrix in governing sleep replay during sleep prior to experience
neocortical inputs randomly active ->
hippocampal neurons randomly connected to each other ->
hippocampal output = random spiking following cortical activation
Explain the interaction between inputs and synaptic matrix in governing sleep replay during waking behaviour
visual cortical inputs sequential to places visited ->
hippocampal place cells activated sequentially ->
synaptic matrix is asymmetric = earlier activated neurons make stronger synapses on later ones
Explain the interaction between inputs and synaptic matrix in governing sleep replay during sleep post-experience
neocortical activity is unstructured and synchronous (not taking in sensory info) ->
hippocampal matrix asymmetric (result from recent experience) =
hippocampal spiking that resembles activity sequence during behaviour (compressed timeline) ->
consolidated into neocortex
How can odour cue memory consolation in SWS?
when exposed to an odour during a task, exposure to the same odour during SWS shows improved memory for the task
*exposure to odour during REM or awake showed no benefit
How can sound cue memory consolation (spatial location)?
better spatial location retention for cued compared to uncued objects after sleep for an object location task while hearing object sounds
How can sound cue memory consolation (rats)?
a rat trained to run to the left side in response to sound L and the right side in response to sound R
during sleep, when sound L was played, neurons associated with the left part of the arena preferentially reactivate (same for R sound -> associated neurons reactivated)
What is the physiology behind sound cueing memory consolation (rats)?
the acoustic stimulus is processed in neocortical auditory areas, and activity in these areas presumable triggers the replay of hippocampal neuronal activity associated with the sound
the hippocampal replay promotes system consolidation (long-term storage)
*Sound-modulated replay of neural activity of the behaviour
What do memory consolidation experiments demonstrate?
memory consolidation is an active and selective process
What are the three field potentials associated with memory consolidation in SWS?
- cortical delta rhythms <4Hz amplitude
- thalamo-cortical spindles, brief 12-14 Hz waves
- hippocampal sharp wave-ripples, brief 80-200Hz oscillations
What drives long-term storage of memories during SWS?
they are repeatedly reactivated, driving gradual redistribution to long-term storage in the neocortex
What does systems consolodation during SWS rely on?
the dialogue between the neocortex and hippocampus under top-down control by the neocortical slow oscillations
The depolarizing up phases of the slow oscillations drive the repeated reactivation of hippocampal memory together with sharp wave ripples and thalamic-cortical spindles
What does the synchronous drive of the three field potentials associated with memory consolidation in SWS allow for?
the formation of spindle ripple events, where sharp wave-ripples and associated reactivated memory information becomes nested into succeeding troughs of spindles
*fine tuned communication during NREM sleep
Why can the thalamus generate rhythmic activity?
because of the intrinsic properties of its neurons and its synaptic interconnections
How do reticular cells in the thalamus cause spikes in thalamocortical cells?
reticular firing acts on thalamocortical cells by removing the inactivation on Ca2+ channels -> spiking of thalamocortical cells
reticular cells also stabilize thalamocortical cells by releasing GABA (inhibit)
What is the glymphatic system?
provides a flow of CSF through the interior of the brain that helps to clear cellular debris, proteins, and other wastes
by removing harmful substances it may protect us from various neurological diseases
Explain the pathway of CSF in the glymphatic system?
- CSF flows from the subarachnoid space into the periarterial spaces surrounding fine arterioles and is propelled by pulsing of artery walls
- CSF enters the brain tissue via aquaporins in the end feet of astrocytes surrounding arterioles, then flows through the brain, accumulating waste material as it goes
- CSF then drains into the perivascular space surrounding the brain capillaries, ultimately joining the circulatory system
What is the function of tghe glymphatic system?
convective glymphatic fluxes of CSF and ISF propel the waste products of neuron metabolism into the paravenous space from which they are directed into lymphatic vessels and ultimately return to the general circulation for clearance by the kidney and liver
What drives the movement of CSF through the interstium?
pulsatility of the artery walls
What happens to the movement of CSF and clearing wastes with beta amyloid plaques?
beta amyloid plaque formation is associated with an inflammatory response
plaques impede the directional glymphatic flow and impair waste clearance by blocking the outflow of CSF into the interstitium and the uptake into the paravenous space
What can impede the directional glymphatic flow and waste clearance?
age-related decline in CSF production
decrease in perivascular AQP4 polarization
gliosis
plaque formation
At what sleep stage is glymphatic flow the highest?
stage 3 (SWS)
NREM
progressivles less towards awake state
What decreases glymphatic flow in older adults?
lack of stage 3 NREM sleep
frequent interruptions of stage 1 and 2 NREM sleep
shorter total sleep time
a number of conditions and disorders can suppress glymphatic function during NREM sleep, further exacerbating the effects of glymphatic dysfunction in neurodegenerative diseases
How does interstial space change during sleep?
sleep is associated with a 60% increase in interstitial space
How does an increase in interstitial space during sleep affect glymphatic flow?
results in better CSF flow and more effective (faster) clearance of metabolites during sleep
* CSF flow is restricted and metabolites accumulate when awake
What is the function of the diffuse modulatory neurotrasmitter systems?
regulate sleep and wake transitions
send afferent projections to the thalamus
What is the function of acetylcholine to regulate sleep/wake transitions (brain regions, waking, SWS, REM levels)?
brain regions: pons, basal forebrain, medial septum
waking levels: high
SWS levels: low
REM levels: high
What is the function of norepinephrine to regulate sleep/wake transitions (brain regions, waking, SWS, REM levels)?
brain regions: locus coeruleus
waking levels: high
SWS levels: low
REM levels: low
What is the function of seretonin to regulate sleep/wake transitions (brain regions, waking, SWS, REM levels)?
brain regions: raphe nuclei
waking levels: high
SWS levels: decreasing
REM levels: low
What is the function of histamine to regulate sleep/wake transitions (brain regions, waking, SWS, REM levels)?
brain regions: tuberomammillary nucleus
waking levels: high
SWS levels: low
REM levels: low
What is the function of orexin to regulate sleep/wake transitions (brain regions, waking, SWS, REM levels)?
brain regions: lateral hypothalamus
waking levels: high
SWS levels: low
REM levels: low
How does thalamic rhythicity chage from sleep to waking states?
NREM - thalamus and cortical neurosn are synchronized (generating slow, delta rhythms of intrinsic burst firing
awake - supression of rhythmic firing, becomes unsynchronized, under influence of Ach, NE, and histamine, neurons depolarize and switch to a more excitable single spikng mode
What is the majow sleep promoting region?
ventrolateral pre optic neuclues (VLPO)
Explain the flip-flop circuts for sleep/wake transitions
The VLPO and major wakefulness promoting regions are reciporcaly connects by inhibitory GABAergic neurons
- in the wake state the arousal systms area active and VLPO is inhibited
- in the sleep state the VLPO is active and arousal systems are inhibited
How do orexin neurons stbailize the sleep/wake flip-flop circuit in the waking state?
When activated it promoted the wakefulness state by furhter activating arousal systems
*stabaizes the system
What is narcolepsy?
a disorder that involved frequent, intense episodes of sleep, which last from 50 to 30 minuets and can occur anytime during the usual waking hoursW
What is cataplexy?
sudden loss of muscle tone, leading to collapse of the body wihtout loss of consciousness
What is the neural degeneration of narcolepsy?
far less hypocretin neurons
What is sleep onset in naroclepsy associated with?
sudden decrease in muscle tone and the appearance of rapid eye moevments typical of REM sleep
Explain the neural control of transition to REM sleep
REM sleep flip-flop circuit
VlPAG (REM-OFF) is activated during NREM sleep
SLD (REM-ON) is activated during REM sleep
reciprocal inhibition (only one region can be on)
* go to notes for diagram
How do EMGs chagne from NREM to REM sleep?
low frequency and high amplitude to high frequency and low amplitude
What drives motor commands during wake periods?
primary and premotor cotices, with modulary basal ganglia input, and brainstem motor pattern generators, project to spinal motoneurons to drive motor behaviour
What occurs to motor behaviour during REM sleep?
the sublaterodorsal tegmental nucleus projects sirectly to inhibitory spinal interneurons as well as through the ventromedial medulla to inhibiot spinal motoneurons and enforce atonia (paralysis)
What is REM sleep behaviour disorder?
degeneration of the sublateraldorsal tegmental nucleus (SLD) and/or ventromedial medulla (VMM) relseaes this inhibitons results in inappropriate motor activity during REM sleep
often progressed to neurodegeneratice disease
no/less inhibitions of lower motor neurons
What are characteristics REM dreams?
longer
visual
emotional
not related to life/reality
feelings of experience
reported to be vivid
What are characteristics NREM dreams?
shorter
less visual and emotional
related to life/reality
report fewer (less memory)
What brain regions are active during REM sleep to wake?
frontal lobe
exttra striate
What brain regions are active during REM sleep to SWS?
high limbic
What is brain acitivty like during sleep walking?
no frontal function
stage 3 sleep
no memory
