Lecture 13 Flashcards
EEG
electroencephalogram
electrodes on scalp
average activity of neurons under the sensors
EMG
Electromyogram
On chin to record muscle tension
EOG
Electro-oculogram
Around eyes for eye movements
Why not just use EEG?
If it is slightly misplaced, invalid. Therefore, 2 or more is more accurate
Eye movement in sleep
In all phases but much more in REM
Sleep cycle
Every cycle, deep sleep drops and rem increases
The last hour is usually spent in REM
People can dream in any stage but we remeber REM better
Sometimes after REM, people wake up and go to sleep again then do not remember doing so
Stage 1-2
Light sleep
Stage 3-4
Slow wave sleep
Large amplitude, low frequency waves
Synchronized across many neurons
REM
Desynchronized EEG activity muscle paralysis Dreaming apart from twitching, muscles are active cerebral blood flow/oxygen demand increases
Beta activity
12-30 Hz
Aroused state
dyssynchronous
high f, low A oscillations
Alpha activity
12-12 Hz
Awake but relaxed
Theta activity
4-8Hz
Intermittently when people are drowsy and is prominent in early stages of slow-wave sleep
Possibly REM activity
Delta activity
less than 4 Hz
deepest stages of slow wave sleep
synchronized, low frequency, high A brain activity
REM deprivation studies
Put rat on a pedestal surrounded by water
When they fall asleep and enter rem sleep, muscles relax and they fall off/ wake up
Shows loads of results:
Turns out they are all due to stress cos sleeping on a pedestal is shit
Lack of sleep study
One rat allowed to sleep, other when he does, platform moves and wakes him up
Food intake goes up but bodyweight drops
Sleep deprived animals loose control of metabolic processes
Eventually die
Sleep is critical for survival
Feel tired but physically fine
Mind deteriorates
Low reaction time and poor judgement (on cog tests)
Increase in stress hormones, mood swings and impulsive behaviour
Worse learning and memory
Increased chance of weight gain, migraines, hallucinations, dementia, seizures and death. Weight loss of very deprived.
Sleep debt must be repaid (in most species) to an extent
Microsleep states occur, during which time they are blind and unaware they fell asleep (trucker accidents)
Precede or exacerbate mental illness diagnosis (don’t know which comes first)
Animals sleep in different ways
Dolphins alternate between hemispheres
If one side racks up a debt, that side must pay
Developmental differences within species
50% of infant sleep REM
25% of adult
Between species differences in sleep
Amount of sleep
Ration of REM to non-REM sleep
Length of sleep cycles
Animals preyed on sleep in short cycles that might last only a few mins
Sleep and body weight correlation
Amount of time a species sleeps is inversely proportional to its weight
Metabolic rate and body weight correlation
While overall B
Correlation between metabolic rate and sleep
High bodymass: High brain mass: High overall BMR but low metabolic rate per kg, low heart rate, increased lifespan, less total sleep time, increased length of sleep cycles
Might all be economies of scale to heat savings and nutrient/waste distribution networks with larger animals benefitting
Fact that total sleep time is correlated with all of these suggests sleep may be critical for restorative processes
Hypothesis: Recover from physical exertion
Amount of sleep does not correlate with exercise amount
Calorific difference between humans sleeping and sitting is negligible over 8 hours (110)
Sleep does lower BP (25%) and HR (15|%) but not enough to cause a kcal drop
No link between cognitive exertion and sleep either
Hypothesis: Brain Processing
Gives brain a chance to reorganize data and archive memory
Learning and memory are impacted by sleep
Synaptic modifications do occur in sleep
During sleep, brain actively processes information and transfers it both within cells (with gene transcription) and between cells via network oscillations
With PCs have to chut down and reboot. Does brain do this?
Although the date is there for this, it does not do enough to make it a function for sleep
Stages of sleep
Sleep talking is usually slow wave (muscles not paralyzed) and is more common in the first part of the night
Most of our time is spent in deep or REM sleep
Maybe 2 systems need to process things offline
Deep sleep - declarative
REM - procedural
Hypothesis: Waste Management
Fact that sleep time is correlated with (body mass, brain size, metabolic rate, HR, life span) suggests it might be due to waste management
It has been reported that the concentration of proteins in the brain increases across periods of wakefulness and drops after periods of sleep
Research shows that the clearance of proteins and waste products is almost nonexistent in wakefulness but really high during sleep
So why do animals sleep?
Volume of interstitial space goes up by 60% across sleep/wake cycles and goes from 14 to 23%. Promotes diffusion of CSF into the brain and so clears waste
Why do big animals sleep less? Maybe the clearance of waste from the brain benefits from economies of scale.
The glymphatic system’s clearance of proteins and waste is nearly nonexistent during waking hours but high in sleep. Bodies lymphatic system is always active.
Why did we not evolve bigger brains with diffusion all the time?
- We do not know
- All signaling molecules in the brain act via diffusion and putting restraints on diffusion is a prominent aspect of regulatory control
- Promoting or constraining diffusion may be one of the principle ways brains function is regulated
- So may be an evolutionally pressure to control and contain diffusion within the brain such that waste products cannot be cleared during waking hours
- So sleep evolved to allow the brain to clear this out and let the brain perform optimally for the rest of the day
Circadian Rythms
24 hour process
Daily light levels regulate this
If we shift the light, rats cycles act
If the light is constant and dim, the rat finds its own source of rhythmicity due to an internal clock. They will maintain it but over 23 or 25 hours. A brief period of light will reset it.
Suprachasmic Nucleus (SCN)
In hypothalamus below optic chiasm
GETS INPUT AND MEASURES LIGHT BUT DOES NOT PROCESS IT
This nucleus will set its own time if no light but it isn’t perfect\Uses light to reset to 24 hour
Lesioning messes this up but does not change the total sleep time
How does the SCN work?
two feedback looks
when expression of one protein gets high enough, it inhibits itself and promotes the production of another
Sleep disorders
Advanced sleep phase syndrome - mutation of per2 gene causes a four hour advance. Falls asleep at 7pm and wakes up at 4am
Delayed sleep syndrome - per3 mutation. 4 Hour delay. Sleeps at 2am and wakes up at 11am
