Biological Psychology - Sleep

Ultradian Rhythm

A cycle less than 24hrs. 90 minute BRAC (basic rest / activity cycle). Can become more or less alert during the day - 90 minute waves of more sleepy and less sleepy. 90-120 minute sleep stage cycles. Hormones, heart rate, temperature and appetite vary in their ultradian rhythms.

Hobson's Activation-Synthesis Theory

Holds that the order within dreams is a function of beliefs, memories and parts of the brain trying to make sense when the visual cortex is activated, but the rest of the brain isn't. The brain is trying to make sense of this happening.

Narcolepsy

Hypersomnia, it is frequent periods of sleepiness affecting around 1 in 2000 people. Main symptoms are gradual or sudden attacks of sleepiness, cataplexy (muscle weakness triggered by strong emotions), sleep paralysis (an inability to move whilst waking up), hallucinations (dreamlike experiences the person has difficulty distinguishing from reality when going to sleep or waking up). Can be treated with stimulants (modafinil or dexamphetamine). Can affect animals, particularly dogs. There are similarities between narcolepsy and REM sleep - a 90 minute cycle, cataplexy is similar to the muscle tone loss and active muscle inhibition in REM sleep, hallucinations are like REM dreaming. There is no reason for the emotional trigger though, so it is not like REM in that sense.

Sleep Disorders

Hypersomnias (too much sleep), hyposomnias (too little sleep), parasomnias (everything else). The pathophysiology of many sleep-wake disorders is poorly understood. They are generally a combination of biological, pyschological and social factors (Schwartz & Roth, 2008).

Drugs Affecting Sleep

Hypnotics - promote or increase sleep, like benzodiazepenes (valium, librium, etc.). They can provide short term relief, but are not recommended long term as there is an addiction potential. They also have a rebound effect, producing insomnia rather than treating it, so there is a need to take more to overcome this problem. Anti-hypnotics - reduce sleep like cocaine derivatives, amphetamines, antidepressants and SSRIs. They increase DA, noradrenaline and adrenaline, suppressing REM. Alcohol - increases SWS and suppresses REM in the first half of the night, followed by a REM rebound in the second half. A change in the balance of REM sleep is disruptive and reduces sleep quality.

Prolonged Sleep Deprivation

Illness and eventually death in rats (Rechtschaffen et al, 1980s). Human generic condition of fatal familial insomnia - a genetic mutation in families that stops the person sleeping properly. Less than 5hrs or more than 9hrs results in a 15% increased risk of mortality (Kripke et al, 2002).

Procedural Memory

Implicitly knowing 'how' to do something - it's dependent on REM sleep. Greater REM in infancy for new learning. The distinction between declarative and procedural memory may be simplistic - for some, procedural task optimal performance occurred after both SWS and REM were experienced (Gais et al, 2000).

Sleep and Mood

Increased depressive mood in students sleeping less than 6 and three quarter hours compared to over 8 and a quarter (Wolfson and Carskadon, 1998). Weekend fluctuation is linked with depressive mood. Children with sleep problems are 60% more likely to suffer anxiety disorders aged between 21 and 26 (Gregory et al, 2005). Most studies into this are questionnaires, so cannot determine causality, but treatment of sleep problems often leads to improvements in mood (Dahl, 1996).

Adaptive (Circadian) Theories

Meddis (1977) believed sleep was a behaviour developed through evolution that keeps animals safe during inactive periods and conserves energy. Alison & Chichetti (1976) found that the size of animal and danger of attack accounted for 58% of the variability in length of sleep between species. But bigger animals have less energy loss than smaller ones (e.g. humans vs mice), so don't have the same conservation needs. Advanced animals can adopt relaxed wakefulness so sleep adds little to energy conservation compared to resting.

Sleep Dependent Memory Consolidation

Memories are better consolidated during sleep compared to awake (we move experiences into long term memory through sleep). Neural pathways are reactivated during sleep, transferring new memory traces from the hippocampus to the cortex. Even a nap can be sufficient to do this.

Sleep & Other Cognitive Functions

Motor functions - hand-eye coordination deteriorates with sleep deprivation (Williamson & Feyer, 2000). Speech - verbal fluency and articulation (Harrison & Horne, 1997). Language - snoring and poorer performance in language subjects at school (Andreou & Agapitou, 2007). Driving ability - 20% of motor accidents occur between midnight and 6am.

Why We Sleep

No universally agreed upon theory, but main theories are - recuperation and adaptation.

Moruzzi & Magoun's Active Theory (1949)

Now known to be an active process characterised by a distinct cyclical pattern of neural activation and deactivation - cutting sensory input does not induce sleep.

Parasomnias

Para means around sleep. REM Behaviour Disorder (RBD) happens when sleep occurs without normal atonia, so the person acts out dreams. Periodic Limb Movement Disorder (PLMD) affects around 10% of children and adults. These are common in children, but usually outgrown - night terrors (pavor nocturnus) usually occuring in NREM sleep; sleep talking (somniloquay) occurs in both REM and NREM sleep; sleepwalking (sonnambulism) runs in families and occurs in SWS, it is distinct from RBD because it is not acting out a dream; bedwetting (nocturnal enuresis) which can be cured with training. Sleep paralysis is common in narcolepsy as well as parasomnia.

Polysomnography

Participant stays in sleep lab overnight. Channels measure EEG (electroencephalography), EOG (electro-occulography - the movement of the eyes), EMG (electromyography - tone of muscles), respiration. The 'gold standard' sleep test, but expensive, labour intensive and time consuming to analyse. Not suitable for everyone as some people have trouble with the sensors, which produces abnormal sleep for them.

Short Sleep

People who can function on very little sleep - it's most likely down to their genes (p.Tyr362His - 'the Thatcher gene'?).

Methods of Measuring Sleep

Polysomnography (PSG), actigraphy, pulse oximetry, questionnaires, Epworth Sleepiness Scale.

Sleep and Executive Functions

Prefrontal cortex is sensitive to sleep disruption which controls functions of planning, inhibition, working memory, problem-solving, goal-directed behaviour, etc. Longer sleep periods in children (even half an hour) can accelerate their development (half hour by two years - Sadeh et al, 2003).

Sleep Deprivation

Recovery from a prolonged period of deprivation (3 days or more) sees changes in SWS (increases) and REM (rebounds). Randy Gardner spent 264 hrs awake (11 days) trying to break the record for staying awake in the sixties. Researchers observing him afterwards saw cognitive and behavioural changes including loss of concentration and short term memory, moodiness, short temper, paranoia, hallucinations and delusions (although hallucinations were not psychotic). He spent more time in SWS and marked REM rebound and never fully recovered the sleep he lost. There are ethical issues around sleep deprivation procedures and it has been found to affect mental processes over physical ones.

Epworth Sleepiness Scale

Scoring on a scale of 0 to 3. Questions concerning how likely the test subject would be to fall asleep during a number of situations. Final score is the addition of items - if the score is over 10, it suggests excessive daytime sleepiness. Daytime sleepiness is related to nocturnal sleep problems and curtailment of sleep.

School Performance

There is a link between sleep, attention and executive performance. Daytime sleepiness as a result of poor sleep shows strongest link with school performance, particularly for younger children (Dewald et al, 2010). Students with higher grades report longer, more regular sleep and earlier bedtimes on school nights, along with less weekend fluctuation than their peers with poorer grades (Wolfson and Carskadon, 1998).

REM & Dreaming

There is a strong correlation between REM sleep and visual dreaming. Everyone dreams, but dreams aren't always remembered - the probability of recalling a dream falls to 0 within 8 minutes of slow wave sleep after REM, and this is why we usually only remember morning dreams. Dreams are often about relevant things that may have happened during the day - biological psychologists see meaning in the creation of the story and see them like a hallucinatory image, caused by activation of the visual cortex. Dreaming is potentially a side effect of learning and consolidation of memories.

Changes in REM with Age

There is an increase in 'active' sleep in infancy, similar to REM sleep, but not. Need for active sleep starts in the womb. Active sleep fills approximately 60-65% of total sleep time of infants born 2-4 weeks prematurely. Full term infants spend 50% of total sleep time in active sleep. This falls to 40% by 3-5 months old. Children reach an adult level of 20-25% REM sleep by 2-5 years old and show little change in this after 10 years. Active sleep may be to do with brains forming memories and connecting neurons (developing).

Early Sleep Stages

There to transition you into deeper stages of sleep. If you get there quicker, you have more efficient sleep.

REM Sleep

Theta and beta activity - we are asleep, but there is a lot of brain activity. It's known as paradoxical sleep (or emergent stage 1 sleep) due to this brain activity. We lose muscle tone and don't move about. Rapid eye movements characterise the stage. Eye movement can be measured on an EOG. REM sleep gets longer as you move through the night, cycling up and down the sleep stages.

Sleep Wake Cycle

Two process model - homeostatic sleep drive builds during the day driving the body towards sleep and reminding it to do so. The cicadian alerting system from the SCN alerts the body to the time of day (sleep gate). Melotonin rises through the night and decreases towards morning - it is involved in the rhythm of sleep but not sleep itself.

Bremer's Passive Theory (1937)

Until the fifties, sleep was viewed as an inactive state caused by a lapse in waking state when there is insufficient stimulation to keep the brain awake.

Obstructive Sleep Apnoea Syndrome (OSAS)

Upper airway becomes obstructed causing difficulty breathing during sleep. Hypoxia is where oxygen saturation decreases. Hypercarbia is increased carbon dioxide. Results in frequent awakenings and fragmented sleep. Caused by genetics, hormones, old age, obesity or deterioration of brain mechanisms that control breathing. Consequences include sleepiness during the day, impaired attention and depression. Treated with weight loss if obesity is the cause, removal or tonsils and adenoids, positive pressure, a mask at night that increases pressure to keep airwaves open).

How Much Sleep is Needed

Varies from person to person, but an average of 7.5hrs is deemed to be a good quality sleep (quality is as important as quantity).

Snoring

(Archibold et al, 2004; Blunden et al, 2005) Oxygen desturations and associated night wakings.

Actigraphy

Activity monitoring with watches / activity trackers. Can be used in a more natural setting than a lab, including home. The device accelerometer uses an algorithm to calculate each minute asleep or awake. Valid, reliable and non-invasive. .8 concordance with PSG, correlating with what you get from this test.

Circadian Rhythm Disorders

An advanced sleep phase disorder - sleep phases are delayed. This is only a problem when they interfere with every day life and an individual cannot adjust. Possible treatments include bright lights in the morning (chronotherapy) that cause an advance delay sleep phase, melatonin, delaying sleep phase until the desired bedtime is achieved. Jet lag and shift work can cause circadian rhythm disorders, but this is temporary.

Sleep Problems in Atypical Development

Around 80% of children with neurodevelopmental disorders and visual impairments suffer from some sort of sleep problem or disorder. It can have a huge impact on family life if left unmanaged.

Long Sleep

Associated with ill health and early mortality. Only the young should sleep a lot, as we should need less sleep as we get older.

Stages of Sleep

Awake - beta activity (13-30Hz), a fast wave pattern. Relaxed - alpha waves (8-12Hz). Sleep - stage 1 is theta waves (3.5-7.5Hz), stage 2 is sleep spindles and K complexes, stage 3 is slow wave sleep (SWS) or delta activity (< 3.5Hz). We cycle back up the stages, but go into REM rather than back to stage 1. In stages 3 and 4, neurons fire more slowly.

Species Variation in Sleep Length

Bats - 19hrs a day; cats - 14.5hrs a day; horses, goats, sheep - 2-3hrs. Large herbivores take less sleep, omni and carnivores need more. Nocturnal animals have longer sleep, and burrowing creatures (maybe connected to safety). There is an adaption theory that is sleep patterns due to lifestyle - low nutrients in food sources for large herbivores, so constantly eating, and predators short sleep).

Central Sleep Apneoa

Cessation of breathing during sleep due to a lack of thoracic effort, or the neurological feedback mechanism does not respond quickly enough to CO2. Results in an inability to maintain normal respiration rate, known as periodic breathing. Characterised by periods of hyperventilation followed by no breathing and paralleled by alterations in oxygen saturation of the blood (this is normally 95-100%, but if it drops to 90% it is deemed abnormal). Daytime sleepiness is an outcome. It is different to OSAS in that there is an abnormal drive to breathe, whereas OSAS is characterised by a normal drive to breathe that is obstructed.

Questionnaires

Cheaper than other sleep test methods. Subjective measures of sleep are taken - Epworth Sleepiness Scale measures daytime sleepiness in general, Stanford Sleepiness Scale measures current alertness, Pittsburgh Sleep Quality Index (PSQI) measures sleep quality and disturbance, sleep diaries, Children's Sleep Habits Questionnaire (CSHQ). Subjective measures, so individual may not be aware of own sleep characteristics, with misconceptions about their own sleep. There is also poor concordance between parental reports and objective measures, and questionnaires are reliant on memory.

Biological Rhythms

Circadian rhythm, ultradian rhythm, infradian rhythm.

Infradian Rhythm

Cycle is greater than 24hrs. Hybernation for example.

Circadian Rhythm

Daily cycle of around 24hrs - circadian means about a day long. Internal (endogenous) 'biological clock' governs patterns of behaviour and physiological change. We become trained to external clues (zeitgebers - German for 'time giver') - daylight, for example. Diurnal means active during the day (like humans). Nocturnal means active at night. Crepuscular means active at dawn and dusk (rabbits). Without a light 'clock' they will free run to a 24-25hr cycle. Changes can occur due to jet lag, shift work, etc.

Insomnia

Difficulty initiating and / or maintaining restorative sleep, despite opportunity for a full nights sleep. Most common sleep disorder in children and adults, with a prevalence of around 4% (but figures may be inflated by sleep state misperception). Most common in older people who use alcohol, tobacco and caffeine, and can be associated with depression. The treatment is sleeping! Encouraging good sleep habits, but there is also psychotherapeutic treatment too. Categorised as onset insomnia (trouble falling asleep), maintenance insomnia (trouble staying asleep), termination insomnia (waking to early and being able to return to sleep), failure of sleep induction mechanisms or excess arousal.

Good Sleep Hygiene

Do - have a regular schedule, even at weekends; ensure bedroom is cool and dark; use dim lighting an hour before bed; exercise a few hours before bed. Don't - use stimulants like caffeine or nicotine; drink alcohol to get to sleep; take daytime naps; watch TV or use a computer an hour before bed; go to bed too hungry or too full.

Pulse Oximetry

Doesn't measure sleep, but is used alongside it. A device is worn on the finger or toe measuring heart rate and oxyhaemoglobin (oxygen saturation of blood). Can be used to screen for sleep apenia (where person stops breathing in the night) and other sleep disorders with oxygen loss in blood during sleep.

Sleep and Physiology

Energy conservation - glycogen restoration in the brain. Growth and repair - a growth hormone is released at the start of SWS. Cardiovascular system - OSAS causes elevation and disregulation of blood pressure with a later risk of cardiovascular disease, organ damage. Immune functions - sleep deprivation makes it more likely to catch colds and takes longer to recover; cortisol suppresses the immune system. Appetite - short sleep duration results in reduced leptin (which suppresses appetite) and elevated ghrelin (which stimulates the appetite); there is a vicious circle between obesity and OSAS. Type II diabetes - cortisol increases following sleep deprivation and this counteracts insulin. A reduction in SWS slows insulin response in glucose and impairs both glucose and carbohydrate tolerance. Affects glucose metabolism as an effect of impaired sleep.

Factors Affecting Sleep

Environmental temperature - too hot is worse than too cold, we are unable to regulate body temperature during REM sleep. A hot bath can help reduce temperature in bed, accelerating temperature fall and helping get into stage 3 sleep quicker. Exercise - do this in the late afternoon or early evening and it is beneficial to sleep. Like a bath, it raises body temperature so it falls at bedtime and triggers sleep. Exercising late in the evening stimulates the heart, brain and muscles and so just delays sleep.

Declarative Memory

Explicitly saying you 'know' something - it's dependent on SWS.

Associations Between Sleep and ADHD

Half of ADHD sufferers experience sleep problems, mainly increased movement, bedtime refusal, obstructive sleep apnea (OSAS). Improving sleep has been found to help other symptoms of ADHD, and deficits often improve after adenotonsilectomy (Andreou and Agapitou 2007; Gozal 2008).

Polyphasic Sleep

Several sleeps a day up until about 3 years old, then we start sleeping only at night (monophasic pattern).

Sleep and Attention

Sleep disturbance leads to problems in attention (Fallone et al, 2001; Gruber et al, 2012). Chronic short sleep deprivation is worse than acute. An increase in weekend 'catch up' sleep indicates weekday sleep deprivation and this is associated with reduced attention (Kim et al, 2011).

Restoration Theories

Sleep enables repair (but of what?). Sleep deprivation doesn't affect physical performance (Takeuchi et al, 1985). Exercise increases SWS but only if a corresponding brain temperature increase occurs (Horne, 1988). Increasing mental activity increases SWS (Horne and Minard, 1985). These findings suggest restoration is cerebral - with increased brain complexity and overall size, sleep becomes less important for energy conservation through immobilisation and more important for cerebral recovery (Horne).

Sleep & Biological Rhythms

Sleep is a naturally occurring state of reduced consciousness, sensory activity and voluntary movement that is needed by all mammals and birds, as well as most reptiles, amphibians and fish. It is an emergent higher brain function.

Electroencephalography (EEG)

Sleep is characterised by frequency, amplitude and the shape of particular wave forms in an EEG. Frequency is the number of cycles per second of a wave pattern (referred to as Hertz). Amplitude is the size of the wave from peak to trough (Voltage).

Changes in NREM with Age

The first and second stages of sleep are known as non-REM sleep. Stage 3 is maximal in early childhood - 25-40% of their sleep time is spent in slow wave sleep. Children have longer sleep duration with shorter sleep cycles. Sleep efficiency decreases with increasing age - older adults wake more at night. They have a mild increase in stage 1 sleep, a marked decrease in stage 3 sleep, and relative preservation of REM sleep (REM and SWS are determined to be most important for quality sleep). Older adults require more time in bed to obtain a quality 7-8 hrs sleep.

Endogenous Clock in Mammals

The internal biological clock is in the suprachiasmatic nucleus of the hypothalamus (SCN). This is a small structure in the centre of the brain with functions of feeding, motivation, sex and sleep. Photosensitive cells in the retina pass light information to the SCN via the retinohypothalamic pathway (this pathway is independent of vision, so blind people are affected too). SCN sends a signal to the pineal gland to release melotonin - the gradual decrease in core body temperature in the evening acts as a signal. Everything is reset in the morning light and serotonin activity promotes wakefulness. Cortisol acts as a 'switch' to switch parts of the immune system into 'daytime mode' - there's a marked increase in it when we wake, but we are not fully sure of what it does when waking and it decreases during the day. The SCN lies above the optic chasm.