22 January 2013
Sleep and Dreams
Professor Glenn Wilson
Historically, it was difficult to study sleep. Not much can be gleaned from observing recumbent persons and questionnaires are no use because people remember little of their experience during sleep. The breakthrough came in the 1950s with EEG recordings of brain electrical activity (“brain waves”) when it was confirmed that sleep is anything but dormant.
When awake there is usually a regular wave of around 10cps, called alpha rhythm. As the person falls asleep the waves become slower and less regular, indicating a state called orthodox sleep. After about an hour, an active pattern returns even though the individual looks deeply asleep. This was dubbed paradoxical sleep because the brain is very much awake, even though muscle tone is low. Because rapid bursts of eye movements occur under the closed eyelids it is often called REM sleep.
Orthodox sleep is interspersed with around five periods of REM sleep of progressively longer duration through the course of the night. About a quarter of adult sleep is REM-sleep, rather more in young children and about half the sleep of newborn infants (it probably begins in the foetus around 30 weeks into pregnancy). REM does not occur in reptiles, appears only briefly in birds, but is strongly evident in mammals, especially predators. Predators generally sleep more than grazing animals because their meals are intermittent and they can afford to sleep without fear of attack.
When people are deprived of sleep for any reason there is deterioration in performance, particularly on tasks requiring sustained concentration, and eventually behaviour becomes shambolic. The individual becomes progressively incoherent and irritable and after a few days may experience delusions and hallucinations. The disruptive effects of sleep deprivation have been used as a basis of persuasion in interrogation (brain-washing). Keeping a prisoner awake through the night and plying them with monotonous questions helps extract confessions (albeit often false).
We need sleep for biological restoration. It promotes cell growth and regeneration and bolsters immune functioning. By shutting down most of the body’s machinery, resources can be focused on repairing damage. Sleep also supports memory consolidation. If people are told that certain learning will be retested 14hrs later, they selectively remember that material, but only after having a sleep (Van Dongen et al, 2012). Mander et al (2011) found that subjects given a 90 minute nap had refreshed learning capacity compared to those who had not slept. The effect was linked to the number of sleep spindles produced by the sleeper (fast oscillations particularly in Stage 2 sleep). The authors believe the spindles reflect a transfer of memories from short-term storage (hippocampus) to “hard-drive” (prefrontal cortex).
If people are woken when REMs commence, depriving them specifically of dream-sleep, the proportion of REM sleep increases to make up what was lost. This suggests that REM-sleep is an essential aspect of sleep. Different sleep phases may have different functions and alternate so that whatever time we have to wake up we will have received some benefit from each. Those whose life style places greater demands on their body (e.g., athletes) seem to require more orthodox sleep; those whose brain is developing fast (children) need more REM sleep.
Our circadian rhythm (day-night cycle) is controlled by an oscillator located in the hypothalamus near to input from the eyes (the suprachiasmic nucleus). This modulates the production of the hormone melatonin secreted by the pineal gland in the centre of the brain (more in darkness). Since the circadian rhythm is entrained by light jet-lag and shift-work confuse it. A second biological clock located in the pons (brainstem), which has a 90 min. oscillation, is responsible for triggering REM-sleep.
Since the circadian rhythm is entrained by light it is confused by jet lag and shift work. Northerly migration may also interfere with sleep patterns. Some historians think that the ancestral norm was to have two sleep periods in the night, with an hour or so of activity in between. Artificial light and industrialisation could have changed our ideas about natural sleep patterns and added to our anxiety about insomnia (Brown, 2006). Perhaps the long winter nights in Northerly latitudes favours segmented sleep, just as early afternoon siestas are common in the long days of the Mediterranean summer.
Bunker experiments show a drift towards a 25 hour cycle as though the brain waits a while for darkness then goes to sleep regardless. This is why rotating of shift work towards later bedtimes makes for easier adjustment than anti-clockwise schedules The total proportion of time spent in sleep (around one-third) does seem to be something of a biological imperative. It may even be possible to have too much sleep; one study found that 11 hrs led to diminished performance on exacting tasks compared with the usual 8 hrs, while another found mortality was lowest for people who slept only 7 hrs per night (Kripke et al, 2002).
Insomniais a widespread problem. It is linked with conditions such as depression and chronic pain but occurs also in otherwise healthy people. It may be due to temporary life circumstances like a broken love affair or anticipation of an exciting event. However, some people (chronic worriers) have difficulty sleeping regardless of circumstances, while others (e.g., psychopaths, who feel no anxiety even when they ought to) tend to be “good” sleepers.
Sleep difficulties increase with age. This is partly because of accumulating aches and pains but older people often need less sleep than young people without realising it. They lie in bed tossing and turning when they might be better to reduce their sleep time. More women complain of sleeplessness than men and more married people than single, suggesting that partner snoring is often responsible.
Complaints of sleeplessness are often exaggerated because it is easier to remember the times we are awake during the night than the times we are asleep. When insomniacs are observed in a sleep lab their EEG records often suggest that their sleep pattern is fairly normal even though in the morning they maintain they hardly slept a wink. Various devices for monitoring one’s own sleep patterns are marketed (e.g. mobile phone aps connected with forehead electrodes).
The use of hypnotics (sleeping pills) is widespread but probably unwise. Not only are they fairly ineffective in terms of increasing sleep times but much the effect they do have is placebo (Huedo-Medina, 2012). They may also interfere with sleep by reducing the amount of time spent in REM or deep sleep. Many are addictive (including barbiturates, benzodiazepines, z-drugs and melatonin) and have unpleasant side-effects, including memory impairment and fatigue. When eventually stopped, there is reboundwhich can include vivid dreams, nightmares, anxiety and insomnia worse than that experienced initially.
How should insomnia be dealt with? The bedroom should be made cool, dark and quiet and should be reserved strictly for sleeping (and sex). All office equipment should be removed, especially screens that emit light. Sleep times should be regular and stimulants such as caffeine avoided in the evening. Exercise in the daytime is recommended but not too near bedtime. If one still cannot sleep, then rather than lying there fretting, it is better to get up and do something else until properly tired. It may be a case of adjusting to less sleep as one gets older, rather than battling to retain an old regime. If a particular worry keeps one awake, then it is best to resolve the issue in some way (e.g., writing a letter). If all these measure fail, then cognitive behaviour therapy should be sought.
Sleep apnoearefers to interruptions in breathing during sleep, often connected with snoring and obstruction to the airways. This results in daytime sleepiness and fatigue, accident proneness and susceptibility to a wide range of medical conditions. Treatment approaches include avoiding alcohol and drugs, losing weight, oral devices that maintain open air passages, singing and playing wind instruments that strengthen the throat muscles, like the didgeridoo (Puhan et al, 2006). A small proportion of patients may require surgery.
Narcolepsy is something like the reverse of insomnia. This refers to daytime drowsiness and sudden sleep attacks that can occur at any time of day (often embarrassingly) even if the individual has had a full night’s sleep. Since it may involve vivid dreams and temporary paralysis it appears to be an intrusion of REM-sleeping into waking life. The condition may go with cataplexy – sudden muscular weakness brought on by strong emotion. It is partly hereditary but occasionally linked with head injury or neurological damage (e.g., viral). Various drugs including stimulants and antidepressants may be helpful, as well as controlled daytime naps.
Everybody has dreams, totalling about 2 hours per night and becoming more common towards morning. A few people (6%) deny dreaming but this seems to be because they don’t remember them (they usually do if woken during REMs). Dreams typically last 10-20 mins, about as long as the events would take to enact in real-life. Background stimuli are often incorporated (e.g., a doorbell ringing may introduce a visitor to the dream or music evoke a party scene).
Dreams feature visual content and contain strong emotions (e.g., anxiety and abandonment, but also positive feelings like joy). They may be surrealistic and defy the laws of physics. Usually they depict the dreamer as a central character with little power to determine events (Blagrove, 2009). Lucid dreams (those of which the dreamer is conscious) do permit more control over the narrative. These seem to be a hybrid of REM dreams and waking consciousness (Voss et al, 2009). Some people are able to train themselves to achieve this state and harness them for creative or treatment purposes.
People with disabilities are not usually disabled in their dreams; paraplegics can walk and deaf-mutes communicate normally (Voss et al, 2011). This suggests either some kind genetic programming or the operation of “mirror neurons” which allow copying from observation. However, people who were blind by age 5 do not dream in visual images and also have fewer REMs (Hurovitz et al. 1999). Colour-blind people dream in the colours they experience and older people (who grew up with black and white TV) are less likely to report coloured dreams.
Because dreams occur most obviously during REM-sleep, it has been suggested that the rapid eye movements represent scanning of the dream image and some experiments support this idea. Violent dreams are accompanied by greater REM activity, so both may suggest a high level of brain activity. Dreams do occur during orthodox sleep but are usually shorter in duration and more like day-to-day thinking.
Genital erection occurs during REM sleep, even in infants and older men. This does not depend on a sexual content to the dream; it just reflects the state of the autonomic nervous system at the time. However, it may increase the likelihood of sexual content in the narrative. However, only about 8% of dreams are sexual (Zadra, 2007) the themes reflecting waking interests. “Wet dreams” are common, particularly in adolescent males who do not have sexual release in real life (Yu, 2012).
The “interpretation” of dreams is a creative process in its own right, telling as much about the interpreter as the dreamer. Dreams were seen as inspired by the gods in many ancient cultures, as a way of connecting with ancestors, or as future portents. They can certainly alter the future, as when we “sleep on a problem” and come up with a solution in the morning. The loose associations of dreams can create new ideas (Stickgold et al, 2001); some major discoveries appear to have been prompted by dreams. The involvement of symbolism in dreams has long been recognised. In Genesis Ch.41 Joseph interprets Pharaoh’s dream of 7 lean cows eating 7 fat cows as meaning 7 years of plenty and 7 years of famine.
Freud (1900) maintained that dreams emanated from unconscious desires (especially sexual) but required psychoanalytic interpretation because the symbolisation was there to hide the meaning from the dreamer. Climbing stairs or shooting a gun would be seen as disguised sexual intercourse. The problem for Freud is that some people dream directly of intercourse as well as climbing stairs. Why would they need to suppress it on one occasion and not another? The ancient Greeks actually reversed Freud’s theory. If a Greek dreamed of sleeping with his mother he might conclude that his Motherland was about to bestow an exceptional honour upon him (Eysenck & Wilson, 1973).
Most modern psychologists think Freud’s idea is far-fetched. Eysenck (1957) argued that the purpose of symbolism in dreams is not to avoid the censor, but adjectival (adding colour and precision). You may dream of your mother as a cow or a queen, depending on whether her nutritional or authoritative aspect is emphasised.
Some theorists think the meaning of dreams is “in the eye of the beholder”. According to the activation-synthesis theory of Hobson & McCarley (1977) dreams are the forebrain’s attempt to stitch together random sensations generated by the brainstem during REM sleep. Interpretation is “like reading cookie fortunes”; we find ways of connecting them with our own preoccupations. Hobson’s critics point out that dreams are not random but follow continuous narratives and have recurrent themes. Also, damage to the brainstem does not prevent them from occurring (Solms, 2000). More recently, Hobson (2009) has described dreams as a form of protoconsciousness that begins in foetal life and is a precursor to mature cognition.
The cybernetic theory (Newman & Evans, 1965) views dreams as the experiential by-product of the “off-line” brain discarding junk and shunting important memories into appropriate files where they can accessed again if required. This would account for the fact that dreams are notoriously hard to remember; they are themselves part of a memory consolidation process (Diekelman & Born, 2010). Dreams often connect with the experiences of the day because it is mostly these that are being sorted and stored.
Continuity theory highlights the many similarities between waking thoughts and dreaming. Domhoff (2011) believes we have exaggerated the extent to which they are bizarre and emotional. He hypothesises that dreams arise from a neural system involving the limbic and paralimbic systems and the associational forebrain that is active in mind-wandering and day-dreaming. He calls this the waking default system and lesions to it affect waking thought and dreams in much the same way.
The continuity theory would explain why dreams focus on everyday concerns about the past, present and future. A good example is W.S. Gilbert’s Nightmare Song (from Iolanthe). Although the Lord Chancellor maintains it is unrequited love that “robs me of my rest” and “weaves itself into my midnight slumbers” analysis of the patter shows that his anxiety actually focuses on the things that would annoy a middle-class Victorian man like Gilbert (the stress of public transport, leeching friends and relatives, immature lawyers, business rivals and insecure investments). The song may be fictional but it tells us much about the preoccupations of its author.
The threat simulation theory (Revonsuo, 2000) maintains that dreams and nightmares have an evolutionary function in providing us with a virtual reality in which we can rehearse our reactions to dangerous situations (c.f., the appeal of horror movies). This would account for the fact that a high proportion (80%) of dreams contain threatening themes (Valli & Revonsuo, 2009). Interestingly, major media events do not seem to feature directly. Hartmann & Brezler (2008) found no increase in dreams relating to aeroplanes or tall buildings following the 9/11 attacks, and no exact replays of the events. There was, however, an increase in the overall emotional charge of their dreams.
Non-REM sleep contains interesting phenomena. Enuresis, sleep-talking and sleep-walking occur mostly in deep sleep (Stage 4). Night terrors may be accompanied by sitting up with a look of horror and calling out. Such activities are often accompanied by brief, unpleasant dreamlike experiences suggesting that the individual is acting out dreamlike thoughts (Arnulf et al, 2009). In REM sleep this would not be possible because the dreamer lacks muscle tone.
Sleep-walking occurs in roughly 4% of the population. It is associated with stress, extreme tiredness, alcohol, OCD and use of SSRI antidepressants but cause and effect relationships are unclear (Ohayon et al, 2012). Serious injury is rare; sleepwalkers usually come to no harm, avoiding obstacles and returning to bed after a few minutes and remembering nothing about it in the morning. There is no great danger in waking a sleepwalker but it can be difficult because they are usually in deep sleep.
Other parasomnias include sleep sex, binge eating, teeth-grinding and violent outbursts in which a partner is attacked. These also occur mostly in deep sleep and nothing is remembered on waking. Sleep disorder has been used successfully as a defence against rape (and even murder) but can be difficult to substantiate, especially if the perpetrator has no family history of sexsomnia and has got out of their own bed and gone elsewhere to commit the act.
Why do we so often have nightmares that involve helplessness (e.g., creatures pressing down upon us) and inability to move the limbs in response to some threat? This is easily understandable when we realise that in dream-sleep we are effectively paralysed, perhaps precisely in order to prevent us from acting out dangerous dreams. The experience of sleep paralysis is associated with being half awake, especially during early REM episode when just falling asleep, and it may account for many reports of ghosts, evil presences, sexual abuse and alien abduction (Santomauro & French, 2009).
The fact that a third of our life is spent in sleep would, in itself, be sufficient justification for studying it scientifically. However, the discovery that it is not just a passive state but a highly active process of profound biological and psychological importance, has led to great efforts in recent decades to further our understanding of it. Despite that, we are far from unravelling all of sleep’s mysteries.
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© Professor Glenn Wilson 2013