lecture 9- sleep

What is the physiological control during wakefulness?

• some processes show natural variability:

  • Brain wave activity

  • Breathing

  • Heart rate

• Others are tightly regulated:

  • Body temperature

  • Blood pressure

  • Blood gases

  • Blood glucose levels

What are the physiological changes during sleep?

• overall physiological demands are reduced

• Bodily processes become more stable:

  • Brain wave activity

  • Breathing

  • Heart rate

• Many show a downward shift:

  • Body temperature

  • Blood pressure

  • Metabolic activity

What are psychophysiological measures?

• electroencephalogram (EEG)- measure electrical activity via small electrodes

• Electrooculogram (EOG)- records eye movements using electrodes by outer corners of eyes

• Electromyogram (EMG)- records muscle activity using electrodes below chin or leg to assess body movement.

What is the first stage of sleep?

From alpha to theta.

• EEG shows mix of fading alpha (8-12Hz) and emerging theta (4-7Hz) activity = slower and more irregular.

• Shift marks onset of true sleep

• EOG records slow rolling eye movements

• EMG shows noticeable drop in muscle tone but some twitches or hypnic jerks may appear

What is the second stage of sleep?

Sleep spindles and K-complexes.

• brain activity slows further and body goes into deep relaxation

• Typically last longest proportion of sleep cycle

• EEG shows theta waves punctiated by 1-2 second burst of high frequency 12-14Hz activity= sleep spindles

• K complex can be observed- high amplitude pattern of brain activity

• EOG-eye movements stop

• EMG - muscle activity decreased further, steady but reduced

What is the third stage of sleep?

Deep sleep/ slow-wave sleep.

• marks deep restorative sleep where growth and repair occurs

• Hardest stage to wake from, disorientation common if awakened.

• Sleepwalking and night terrors tend to occur here

• EEG- dominated by delta waves, slow high-amplitude activity

• EOG- eyes still

• EMG- very low muscle tone, fully relaxed body

What is the last stage of sleep?

Rapid eye movement/REM sleep.

• occurs about 90 mins after sleep onset, repeating several times through night

• Brain highly active

• Most vivid dreaming occurs

• EEG- low voltage, mixed-frequency resembling wakefulness

• EOG- burst of rapid eye movements beneath closed eyelids

• EMG- near complete loss of muscle tone (atonia), body effectively paralysed.

What are sleep cycles?

• sleep alternates between stages 1-3 and REM roughly every 90 mins

• Early cycles= larger proportion deep N3 (slow wave)

• Later cycles- larger proportion REM, 3 decreases

What are the main sleep theories of why we sleep?

• recuperation theories

  • Restore physiological balance disrupted by wakefulness.

  • Being awake uses energy and stresses bodily systems, sleep repairs, recovers, replenishes

  • Maintaining homeostasis

• Adaptation theories

  • Evolutionary adaption

  • Evolved as part of 24 hour biological rhythm- circadian cycle

  • Sleep to avoid harm and conserve energy when activity would be least effective or most dangerous

What happens when deprived of sleep?

• cognitive- poor focus, memory relapses, slower reactions

• Emotional- irritability, stress intolerance, low mood

• Social/behavioural- reduced motivation, poor judgement

• Physical- immune suppression, appetite disruption, fatigue

What are the neurocognitive consequences of sleep deprivation?

• universally reduces daytime performance

• Causes microsleeps, lapses, attention failures due to wakefulness EOG-state instablity

• Impairs key cognitive domains- executive attention, working memory, higher order reasoning

• Prefrontal cortex functions are vulnerable

• Effects worsen over time

What is the sleep - deprived students case study?

• students kept awake for several nights

• Initally managed to study until 3am, strong sleepiness set in

• Next day remained fairly alert when active, struggled to focus during quiet tasks at night

• Cycle repeated

• Shows the sleep-wake rhythm persists even without actual sleep- internal adaptive clock

• Increasing fatigue and concentration problems support recuperation theory

What is the case study of Randy Gardner?

• 17 year old student attempted to break world record for wakefulness- stayed awake for 11 days

• Showed severe lapses in attwntion and motivation

• Distorted perception and mood changes

• Impaired cognitive and motor performance

• After few nights of recovery sleep, normal functioning returned- recuperation. Lost sleep leads to deficits reversed by rest.

• On first recovery night, he slept 14 hours

• After that quickly returned to 8 hour routine.

• Didn’t need to repay full sleep debt

• Sleep controlled by adaptive timing mechanisms

Is sleep a state of adaptive inactivity?

• adaptive behaviour shaped by ecological and evolutionary pressures

• Variation in duration cannot be explained by recuperation alone

• Predators sleep much more And mammals with lower risk of predation e.g. sloths

• Also correlated with metabolic rate and foraging needs

• Higher energy demands may sacrifice sleep to maximise feeding

Do all animals sleep?

• evidence is less clear for reptiles, dish, invertebrates

• Some species exhibit sleep like states without classic EEG

• Possible that sleep serves different functions in different groups

• Challenges idea of recuperation

• Sleep is flexible, forms that suit species adaptive survival needs

What evidence is there that birds sleep mid-flight?

• birds can sleep with one hemisphere while keeping other awake during flight- unihemispheric sleep

• Adaptive solution to balance rest with ecological demands.

What are the main limitations of adaptive theories?

• largely drawn from animal studies/ observation

• Less directly testable

• Sleep had costs like predation or lost foraging opportunities

• Doesn’t explain how lack leads to physiological and neurocognitive collapse

Why do we dream?

• early civilisations- medium between earthly world and the Gods

• Greeks/romans- dreams had prophetic powers

• Aristotle- dreams arise from continued movements of sensory organs during sleep

• Physiological theories

  • Freud

  • Threat-simulation theory

  • Expectation-fulfiment theory

• Neurobiological theories

  • Activation-synthesis theory

  • Continual activation theory

What is Freud’s psychological theory?

• dreams triggered by unacceptable repressed wishes, often of sexual nature

• Dreams we experience (manifest dreams) are Disguised versions of real dreams (latent)

• To understand people, expose meaning of latent dreams by interpreting manifest dreams

• No convincing evidence

What is threat-simulation theory?

• dreams often contain threatening scenarios that prepare us for dealing with threats

• When rehearsed during dreams, neurocognitive mechanisms for perception and avoidance can be trained.

• Children’s dreams are particularly threat-laden- rehearsal is most adaptive in early development

• However many dreams are non-threatening

What is expectation-fulfilment theory?

• dreaming allows emotional arousals that haven’t been expressed during day to be discharged

• Can free up space in brain to deal with tomorrow’s emotional cues

• Dream content is emotional charged and reflects waking concerns

What is activation-synthesis theory?

• info supplied to cortex during REM sleep is largely random

• Dreams are the cortex’s effort to make sense of the random signals

• Fragmented and unusual nature of dream narratives supports idea of cortex synthesising incoherent neural signals

• Changes in neurotransmitter activity underlie REM physiology, aligning with AST’s mechanistic account

What is continual activation theory?

• The continual-activation theory- function of sleep is to process, encode, and transfer data from short-term memory to LTM through called consolidation.

• also NREM sleep processes conscious-related memory (declarative memory) and REM sleep processes the unconscious-related memory (procedural memory).

• Research strongly supports the role of sleep, particularly REM and slow-wave sleep, in memory consolidation.

What is the role of hypothalamus in sleep?

• constatin examined dead victims of serious viral infection - encephalitis lethargica - which led to the deaths of about 1.5 million people in 1915-1926 epidemic.

• majority of patients slept for more than 20 hours per day, arising only to eat and drink. cognitive function was intact, but they would soon return to sleep.

• A minority of patients had difficulty sleeping.

Individuals with excessive sleep symptoms had damage in the posterior hypothalamus. 

• Individuals with the opposite problem (i.e. insomnia) had damage in the anterior hypothalamus.

What is reticular formation?

• Bremer experimented in cats, severing their brain stem in several areas:

1. Transection between the inferior and superior colliculi to disconnect their forebrains from ascending sensory input → continuous SWS.

2. Transection (cutting through caudal to    the colliculi (“encéphale isolé”, or isolated brain) cutting most of the same sensory fibres → normal sleep cycle

• structure involved in wakefulness was located somewhere in the brainstem between the two main transections. 

• Partial transections at the cerveau isolé which severed the reticular formation core but left sensory fibres of the brain stem intact produced continuous SWS.

• Sensory input from body (e.g., pain, temperature etc.) is insufficient for waking.

• Must be an internal ascending arousal system.

• Electrical stimulation of the reticular formation of sleeping cats awakened them

• Proposed that low levels of activity in the reticular formation produce sleep and that high levels produce wakefulness

• Similarities between REM and wakefulness suggest that the same brain area might be involved in controlling both.

• REM sleep is controlled by nuclei in the caudal (rear) reticular formation, each controlling a different aspect of REM:

  • Atonia (loss of muscle tone)

  • Rapid eye movements

  • Cardiorespiratory changes

What is circadian control of sleep?

• Circadian rhythms are biological cycles that repeat roughly every 24 hours and help coordinate many body functions, including sleep.

• rhythms are driven by the body’s internal clock, located in the hypothalamus. runs slightly longer or shorter than 24 hours.

• needs external cues- zeitgebers, which reset or synchronise the circadian system.

• Light is the strongest zeitgeber, but there are others such as food timing, social routines, and exercise.

Time- deadlines, timetables etc create pressure to stay awake at specific times which can temporarily override homeostatic fatigue signals, keeping the arousal system on.

• Cognitive zeitgebers can: Delay sleep onset, increase arousal in anticipation of events, create misalignment when schedules conflict with circadian rhythms, add to social jet lag

• When cognitive and biological timing are misaligned, the result is poorer alertness, slower cognition, and reduced sleep quality.

• Melatonin - a hormonal zeitgeber released by the pineal gland in a daily, light-sensitive cycle. Levels rise after dark

  • Mainly acts as chronobiotic- shifts timing of circadian rhythm

What is the suprachiasmatic nucleus (SCN)?

• the SCN of the hypothalamus is the circadian clock

• Receives light inputs from retina and resets the clock everyday accordingly to the day-night cycle.

• most active during the day and least active at night.

• Light-induced activation of SCN inhibits the production of melatonin by pineal gland

How does shift work effect sleep?

●In shift work, zeitgebers stay the same but workers are forced to adjust their natural sleep patterns to meet the demands of changing work schedules.

●It can take 1 day for the circadian rhythm to adapt to 1 hour change in light/dark cycle.

●Shift work disorder is related to fatigue, poor performance and poor memory as well as a risk of other health problems

What are sleep disorders?

○Insomnia includes all disorders of initiating and maintaining sleep.

○Hypersomnia includes disorders of excessive sleep or sleepiness.

●Another type of sleep disorders includes those related to REM-sleep dysfunction.  

Parasomnias: abnormal behaviours emanating from or associated with sleep

What is insomnia?

• 16.2% of adults globally have insomnia, and about 7.9% have severe insomnia

• Can be defined in several ways (e.g., sleep onset, frequency of sleep-difficulty, sleep duration)

• Many cases of insomnia are iatrogenic (medically-created) and caused by tolerance and later withdrawal symptoms to sleeping pills

• Other causes can include stress, anxiety, environmental factors, pain, medications etc.

• can be associated with sleep apnea where the patient stops breathing many times each night and only wake up to breathe again and then drift back to sleep.

• Periodic limb movement disorder is characterised by periodic involuntary movements of the limbs, often involving twitches of the legs during sleep, but patients are unawarE

What is narcolepsy?

Disorder of hyper-insomnia characterised by 4 key symptoms:

1. Sleep attacks - overwhelming urge to sleep.

2. Cataplexy - sudden paralysis during which a person remains conscious (often triggered by an emotional experience).

3. Sleep paralysis - inability to move just as one is falling asleep or waking up.

4. Hypnagogic hallucinations - dreams that occur during periods of sleep paralysis.

What are the causes of narcolepsy?

• Orexin implicated

• Reduced levels of orexin found in cerebrospinal fluid of narcoleptics and in brains of deceased narcoleptics

• Autoimmune: Certain genetic variants may cause T-cell to attack orexin-releasing neurons after infection

• Family history is a risk factor. However, only 25% concordance in twin studies so we must be careful not to overstate heritability

What are NREM parasomnias?

Confusional arousals

•Disoriented behaviour during arousal from NREM sleep.

•Last for seconds to minutes.

•Poor recall of events the following day.

Sleepwalking

•Affects up to 17% of children and 4% of adult population.

•Combination of moving with the persistence of impaired consciousness.

•Linked with anxiety, fatigue, alcohol, medications and mental disorders.

What are REM parasomnias?

REM sleeping behaviour disorder

• Loss of normal atonia: dream enactment behaviour

• can often result in injuries

• More frequent in males >50 years old.

• Associated to neurodegenerative disorders (Parkinson’s, dementia).

• Some genetic component.

• Treated with clonazepam, a benzodiazepine.

Isolated sleep paralysis (inability to move)

• Paralysis is maintained after waking from REM sleep.

• can also occur when falling asleep.

• person is fully aware of what is happening.

• can last for seconds to minutes.

• sometimes accompanied by hallucinations.

• first appears during adolescence but most often in 20s and 30s.