Sleep, dreams and consciousness Flashcards
How does an EEG machine work
Electrodes are placed on the scalp and pick up the electric fields generated by neurons
Small voltage fluctuations are measured between selected pairs of electrodes
EEG activity when awake and attentive
Desynchronised, low-voltage high-frequency activity
Gamma and beta rhythms
EEG activity when drowsy or eyes closed
Slowed activity, alpha waves appears at 8-12Hz
EEG activity during stage 1 sleep
Theta waves (4-8Hz) and amplitude increases slightly
EEG activity during stage 2 sleep
Very sharp high-amplitude waves called K complexes, spindles (8-14Hz) in brief epochs involving synchronised thalamocortical activity
Definition of sleep
A condition that typically occurs for several hours every day, characterised by immobility, reduced response to sensory stimuli, rapidly reversible
EEG activity during stage 3 and 4 (deep sleep)
Continuous delta waves (<4Hz)
EEG activity during REM sleep
Similar to awake stage- low voltage, high frequency
Beta and gamma waves
How many times do we cycle through all the sleep stages per night
6 times a night
How do we cycle through the different stages of sleep in a night
Awake -> NREM stages 1-4->NREM stages 4-1 -> REM sleep ->NREM stages 1-4
Each cycle, deep stage sleep is reduced and REM sleep is prolonged
EOG (electrooculogram) recordings at different sleep stages
Awake- rapid eye movement
NREM- slow random eye movements
REM- rapid eye movements
EMG (electromyography) recordings at different sleep stages
Awake- continuous, voluntary
NREM- some episodic involuntary movement
REM- motor output commanded but inhibited (due to atonia)
What happens to a mouse if you keep it in complete darkness
Circadian rhythm maintained but the mice gradually wake up earlier and earlier, because the mouse’s internal clock is slightly shorter than 24 hours
What is the master pacemaker of circadian rhythms
Suprachiasmatic nucleus
What is the result if the suprachiasmiatic nucleus is removed
Circadian rhythms break down, animals show random bouts of activity and sleeping
What happens if an SCN neuron is removed and cultured so they have no input
The neuron’s gene expression patterns continue to oscillate with the circadian rhythm, but this gradually disappears
What is it called the SCN uses retinal input to synchronise the internal circadian rhythm with light-dark rhythms
Photopic entrainment of circadian rhythms
What retinal cells supply the SCN with light-dark info
RGCs
Photosensitive RGCs with melanopsin, project directly to the SCN
What determines phase phenomenon in SCN transplants
The donor animal’s circadian rhythms
eg transplanting a mouse SCN into a human would shift the human’s circadian rhythm to below 24 hours
Match height of brainstem lesions to their effect
Lesions below the pons- normal sleep/wake pattern
Mid-pons lesions- continuously awake
Lesions above the pons- permanently asleep
Why does lesioning different heights of the brainstem cause different wake/sleep disruptions
Different brainstem nuclei act as diffuse modulatory systems, regulating global activity
How does the activity of neurotransmitter released by brainstem nuclei differ across wake/sleep
ACh, serotonin, DA and NA are all most active during wake and less active during NREM sleep
ACh and DA are active during REM sleep
What is sleep homeostasis
If we don’t sleep for a while, sleep pressure builds up
If we don’t sleep for a LONG time, additional sleep pressure builds, and we sleep longer to compensate
Effects of sleep deprivation in humans- all nighter
Fatigue, irritability, impaired memory
Effects of sleep deprivation in humans- world record attempts
Hallucinations, tremor
Effects of sleep deprivation in humans- chronic
Mental health declines, gastrointestinal disorders, increased cancer risk, cardiovascular disorders, all circadian rhythms disrupted
Suggested functions of REM sleep
Memory consolidation and transfer, unlearning ‘parasitic’ memory traces, reinforcement of innate behaviours
What does an EEG record look like
A set of simltaneous squiggles, indicating voltage changes betweens pairs of electrodes
What does EEG measure
The summed voltages generated by the currents that flow during synaptic expectation of the many pyramidal neurons in the cerebral cortex
What detemines the amplitude of EEG
How synchronous the activity of underlying neurons is- simultaneous neuron firing sums their tiny signals to create a larger amplitude signal
What is MEG
Magnetoencephalography- detecting the magnetic signals produced when neurons generate currents
What are gamma rhythms
Fast, 30-90Hz, signal an activated or attentive cortex
What are rippled
Brief bouts of 80-200Hz oscillations
What are beta rhythms
Relatively fast, 15-30Hz
Why is cortex firing unsynchronised during active waking
Each cortical neuron is very active, processing a different aspect of a complex task
What acts as a pacemaker for synchronous neuronal oscillation
The thalamus- has huge cortical input
How does the thalamus produce an oscillatory rhythm
Thalamic neurons can generate very rhythmic APs- some have a particular set of voltage-gated ion channels for this
How do thalamus oscillations act as a pacemaker for neuronal oscillation
The rhythmic activity of thalamic pacemaker neurons are synchronised with one another, then passed to the cortex by thalamocortical axons
A proposed function of synchronised neuronal oscillation
Momentary synchronisation of different brain area firing may allow binding of various neural components into a single perceptual construction eg shape/colour
What state is the ANS in in NREM vs REM sleep
NREM-> parasympathetic nervous system activated, temp and energy consumption lowered
REM->sympathetic activity, heart and respiration rates increase and become irregular
What is brain activity like during NREM sleep
Energy use rate, and general firing rate, are at their lowest point of the day- mental processes are minimal
What is oxygen use like in REM sleep
Oxygen consumption is higher than when the brain is awake and doing difficult maths problems
What fractino of sleep is spent in nonREM
75%
How is nonREM sleep divided
4 distinct stages
NREM stage 1
Transitional sleep (lightest stage), slow rolling eye movements, lasts a few mins
NREM stage 2
Lasts 5-15 mins, slightly deeper than stage 1, eye movements almost cease
NREM stage 3
Slow high-amplitude delta rhythms, eye movements almost cease
NREM stage 4
Deepest stage, delta rhythms of 2Hz or less, may last 20-40 mins in first sleep cycle
What obligatory refractory period exists in sleep cycles
Period of about 30mins between periods of REM
What are ultradian rhythms
Recurrent cycles repeated throughout a 24 hour day
eg sleep cycles
How do bottlenose dolphins sleep
1 hemisphere at a time- 2 hours of NREM sleep on one side, then 1 hour awake on both sides, then switch hemisphere
Effect of sleep deprivation in rats
Rats progressively lose weight while consuming much more food, become weak, accumulate stomach ulcers and die- seem to lose ability to regulate body temp and metabolic needs
What happens if people are repeatedly deprived of REM sleep by waking them up as they enter it
Sleepers attempt to enter REM sleep much mroe frequently than normal
Experience REM rebound when they are allowed to sleep undisturbed, proportional to the duration of their deprivation
What is the activation synthesis hypothesis of sleep
Random pons charge activates random areas of the cerebral cortex, eliciting associations and memories that are synthesized into dreams
What studies suggest REM sleep is important in memory
Depriving humans of REM sleep can impair their ability to learn tasks
Increased duration of REM sleep following intense learning
What neurotransmitters do the brain stem modulatory neurons release during waking
NE and serotonin enhance the waking state
How do the diffuse modulatory systems affect the thalamus
Control the rhythmic behaviour of the thalamus, which in turn controls many EEG rhythms of the cerebral cortex
Why does sensory info to the cortex get blocked during deep sleep
Slow, sleep-related rhythms of the thalamus up to the cortex block the flow of sensory info
How do the brain stem modulatory systems prevent movement during REM sleep
Descending branches of the diffuse modulatory systems inhibit motor neurons during dreaming
What is the ascending reticular activating system
The region of the brainstem containing many sets of ascending modulatory systems- named by Moruzzi after brainstem lesion experiments
What modualory system sets of neurons increase their firing anticipating awakening/during arousal
Locus coeruleus, raphe nuclei, basal forebrain and brainstem, midbrain, hypothalmus
Modulatory systems-what does the locus coruleus release
NE
Modulatory systems-what does the raphe nucleus release
Serotonin
Modulatory systems-what does the basal forebrain and brain stem release
AChs
Modulatory systems-what does the midbrain use as a neurotransmitter
Histamine
Modulatory systems-what does the hypothalamus use as a transmitter
Hypocretin/orexin
What do neurons of diffuse modulatory systems collectively synapse on
Directly synapse on the thalamus, cerebral cortex and many other regions
What is the general effect of diffuse modulatory systems during arousal
Depolarisation of neurons, increasing neuronal excitability, suppressing rhythmic forms of firing
What is hypocretin/orexin
A small peptide neurotrasmitter expressed mainly by neurons whose cell bodies are in the lateral hypothalamus
What do the axons of hypocretin-secreting neurons project onto
Cells of the cholinergic, noradrenergic, serotonergic, dopaminergic and histaminergic modulatory systems
Summarise the roles of hypocretin
Promotes wakefulness, inhibits REM sleep, facilitates neurons that enhance motor behaivour, regulates neuroendocrine systems
What disorder often results from loss of hypocretin neurons
Narcolepsy
What is narcolepsy
Excessive daytime sleepiness, cataplexy (sudden muscular paralysis while consciousness is maintainted ie REM sleep), sleep paralysis
What happens to the firing rates of brain stem modulatory neurons when enter NREM sleep
General decrease in firing rate (NE, 5HT, ACh)
What areas of the brain are more active durign REM sleep than waking
Extrastriate cortical areas, limbic system
What neurotransmitter likely causes the thalamus and cortex to behave like they do in the waking state during REM sleep
ACh released by nuclei in the pons, increased at onset of REM sleep
What is REM sleep behaviour disorder
Individuals act out their dreams due to disruption of the brain stem systems that usually mediate REM atonia
What are some examples of sleep promoting factors
Adenosine, NO, interleukin 1, melatonin
What suggests adenosine is a sleep promoting factor
Caffeine is an adenosine receptor antagonist
Administering adenosine increases sleep
Waking related changes in adenosine only occur in sleep-related regions
What occurs to levels of NO and adenosine throughout the day
Levels progressively increase during waking periods and sleep deprivation, and gradually decrease during sleep
How does adenosine exert its effects as a sleep promoting factor
Adenosine inhibits diffuse modulatory systems for ACh, NE and 5HT that promote wakefulness
May do so by disinhibiting the VLPO
What is adenosine
Neuromodulator released by some neurons and glia, used to build DNA/RNA/ATP
How does NO work as a sleep promoting factor
NO triggers adenosine release
What suggests NO works as a sleep promoting factor (other than causing adenosine release)
Wake-promoting cholinergic neurons of the brain stem express particulalrly high levels of the enzyme for NO
What cytokine has been suggested as a sleep promoting factor
Interleukin 1 synthesised by glia in the brain and macrophages- levels increase during waking, and peak before sleep onset, promoting NREM sleep even when not sick
What is melatonin
A hormone secreted by the pineal body that is a derivative of the amino acid tryptophan
Why is melatonin been called the ‘dracula of hormones’
Release is inhibited by light, released only when the envronment darkens (when we become sleepy in the evening), peaks in the early morning hours and falls to baseline when we awake
What does melatonin do
Helps initiate and maintain sleep
What are circadian rhythms
The daily cycles of daylight and darkness that result from the spin of the Earth
What physiological and biochemical processes in the body rise and fall with daily rhythms
Body temp, blood flow, urine production, hormone levels, hair growth, metabolic rate
What are zeitgebers
Environmental time cues that allow us to become entrained to day-night rhythms eg light/dark, temp
Where i the SCN located
Consists of a tiny pair of neuron clusters in the hypothalamus, located either side of the midline bordering the third ventricle
What tract provides RGC input
The retinohypothalamic tract
Where does the SCN send output to
Primarily the hypothalamus, thalamus
What is the neurotransmitter identity of SCN output neurons
GABA- presumably they inhibit the neurons they innervate
May rhythmically secrete neuromodulator vasopressin
What is the 24 hour molecular cycle of the SCN based on
A negative feedback molecular cycle based on gene expression eg clock gebes
What does CLOCK gene stand for
Circadian locomotor output cycles kaput
Summarise how the negative feedback molecular cycle works in SCN
Genes are transcribed to produce mRNA and proteins
After a delay, proteins send feedback and interact with the transcription mechanism to decrease gene expression
Cycle lasts 24 hours
How are cells in the body kept having a circadian rhythm?
Cells have their own circadian clock driven by the same gene transcriptino feedback loops driving the SCN clock, but these clocks are unde the control of the SCN
What is the effect of the SCN influencing the ANS, body temp, hormones etc
Each of these processes regulates many of the body’s circadian clocks eg body temp effects the clocks of peripheral tissues
How does the SCN control synthesis and secretion of melatonin
SCN projects to the pineal gland
Which part of the brainstem promotes sleep
The ventrolateral preoptic nucleus VLPO
How does the ventrolateral preoptic nucleus promote sleep
Sends GABAergic outputs to all major cell groups in the hypothalamus and brainstem involved in arousal, primarily active during sleep
Where do orexin neurons have mutual projections with
VLPO neurons- orexin neurons reinforce the arousal system but don’t directly inhibit the VLPO
Where does the VLPO receive inhibitory input from
Noraderaline and serotonin- the arousal systems it inhibits during sleep
What is a flip-flop switch
A circuit with mutually inhibitory elements that sets up a self-reinforcing loop- activity in one side disinhibits itself by shutting down inhibition from the other side
Why may sleep use a flip-flop circuit
Flip-flop circuits tend to avoid transitional states, as when one side begins to overcome the other the switch flips
Sleep-wake transitions ARE abrupt
What is the result of one side of a flip-flop neural circuit being weakaned
Homeostatic forces cause the switch to ride closer to its transition point, meaning increased transitions between sleep/wake eg narcolepsy
What is the result of adenosine reinfocing the arousal system via mutual VLPO projections
Stabilises the flip-flop switch
This may be why narcoleptic people, lacking orexin, have a destabilised flip-flop switch
What is the DMH
The dorsomedial nucleus of the hypothalamus
What dos the dorsomedial nucleus of the hypothalamus receive input from
SCN
What output does the dorsomedial nucleus of the hypothalamus provide
One of the largest sources of output to the VLPO and orexin neurons, mainly GABAergic neurons
What does the dorsomedial nucleus do
Integrates info from the SCN with feeding/temp etc, allowing circadian rhythms to be set at optimal phases for survival
Does the dorsomedial nucleus promote or inhibit sleep
Promotes wakefulness by inhibiting sleep through GABAergic projections to the VLPO and orexin
Very active during wakefulness
What genes are involved in the molecule cycle of gene expression underlying circadian rhythms
Circadian locomotor output cycles kaput (produces CLOCK), cryptochrome (produces CRY), period 1-3 (produces PER1-3), brain and muscle, ARNT-like (produces BMALI1)
