The Stages of the Sleep Cycle

Every night, when you to sleep, you transition through a number of stages, each of which is characterised by different types of brainwave, with a different effect on your sleeping body. Each cycle of sleep lasts 90 - 110 minutes. Let's take a look at the different stages in the sleep cycle. 

NREM Stage 1: alpha - theta waves (4 - 7 hz)

Stage 1 is a very light stage in the sleep cycle, which is it easy to be awoken from. Muscle atonia begins to set in, which causes twitches and hypnic jerks. Hypnagogic hallucinations occur, which often manifest as swirling, abstract colours which hypnotise you into sleep. You begin to lose self-awareness and consciousness and most sensory attachment to the external world as your brainwaves slow.

NREM Stage 2: mixed EEG activity

Stage 2 is marked by the brainwaves slowing even more, and a loss of virtually all muscle tone, so that your body cannot physically act out your dreams when you enter REM (Rapid Eye Movement) sleep. There are brief bursts of higher-level brain activity, known as 'sleep spindles' or K-complexes'. This is a light, dreamless stage of sleep, in which you spend almost half of your sleep time.

NREM Stages 3 & 4 - deep sleep: delta waves - below 4 hz

Stages 3 and 4 of the sleep cycle are known as deep, delta or slow-wave sleep, which is characterised by delta brainwave activity and a complete lack of consciousness. The sleeper is less responsive to external environmental stimuli and less likely to awaken as a result. This is a dreamless stage in the sleep cycle, when somnambulism (sleep-walking) is most likely to occur.

REM Sleep - paradoxical sleep: theta waves

REM sleep is characterised as paradoxical sleep - marked by higher levels of brainwave activity. This is when dreaming takes place. Gamma waves (30 hz and above) may be observed in lucid dreamers, this being a form of brainwave activity associated with higher perception and consciousness. 

REM sleep occurs throughout the sleep cycle. Here is an illustration of a typical 8 hour sleep cycle:

The longest, more intense and vivid dreams take place in the 4th and 5th periods of REM sleep, right at the end of the 8 hour sleep cycle, after approximately 6 hours of sleep. This means this is the optimal time for lucid dreaming to occur. The 4th an 5th stages of REM sleep can last between 45 - 60 minutes.

If you tend to wake naturally (without the use of an alarm clock), it is likely that you awaken directly from a dream, when it is fresh in your memory. It is possible to directly re-enter the dream if you allow yourself to immediately fall back asleep. 

The amount of sleep needed on average differs from person to person, and is also dependent on other variables such as age and general health. Newborn babies require the most sleep (14 - 17 hours per day), while adults tend to require approximately 7 - 9 hours of sleep on average. 

If you awaken with an alarm clock, you risk waking mid-cycle, which can be an unpleasant feeling - and you may miss the last periods of REM sleep, which are perfect for dreaming and more pleasant to wake up from. This problem can be overcome by understanding your sleep cycle, or employing the new technology and apps which can monitor your sleep cycle and wake you up once a cycle is complete.

EEG machines can be used to monitor how long a dream lasts. The EEG machine reads brainwave activity - and as you can see from the diagrams above, each stage in the sleep cycle has it's own distinctive brainwave activity associated with it. EEG brainwave monitoring indicates that dreams which occur in early stages of REM sleep last only a few minutes. As you then transition through different stages in the sleep cycle, including the deep, delta-wave sleep, it is unlikely that you will have a vivid memory of these early, fleeting dreams.The majority of the first sleep cycle is dedicated to non-REM sleep, due to the need to prioritise restful and restorative healing sleep.

Time may be experienced differently in dreams - there may be some time distortion - in particular time dilation, where the passage of time is experienced as being much longer within the dream. Generally, it's likely that dream time is relatively commensurate with real time, but it can be very difficult to judge the length of a dream from the first person perspective. Some people report that their normal, non-lucid dreams are experienced as stretching over days, weeks - even months or years. 

Just like normal, non-lucid dreams, lucid dreams can last from minutes up to the full period of REM sleep (i.e. 60 minutes). Lucid dreams may be cut prematurely short due to heightened arousal and the intense excitement of the experience waking the dreamer up. Lucid dream stabilisation can significantly help in prolonging the lucid dream experience as well as enhancing the clarity of the lucid dream.

There are a number of ways in which you can 'hack' the sleep cycle in order to maximise your chances of successfully experiencing a lucid dream - see The Dreamhacker Series | Hacking the Sleep Cycle (2) for a beginner-level tutorial on this topic.

Below, are some neuroimaging of the brain, showing different levels of mental activity and inactivity during REM sleep and comparisons to brain activity during wakefulness and NREM (delta, slow-wave) sleep.

Cannabis & Dreaming

It is commonly reported by many oneironauts that smoking or ingesting cannabis before sleep dramatically reduces the ability to recall any dreams from that night. When regular cannabis smokers take a break from using cannabis, they often find their dreams are more bizarre and vivid than usual, as a result of the 'REM rebound effect'. 

Cannabis (or marijuana) is known to affect various stages of the sleep cycle, not just REM sleep. Some of the sleep activities affected by cannabis use are not involved in the dreaming process. The chemicals found in cannabis - cannabinoids - closely mimic the activity of chemicals found naturally in the brain. These chemicals and their biological pathways constitute the body's endocannabinoid system which is responsible for regulating sleep; this will be unsurprising to many who are familiar with the effect of smoking or eating cannabis. THC (tetrahydrocannabinol) has been found to ease insomnia and quicken the sleep process for non-insomniacs alike. This was confirmed in a study by Cousens & DiMascio (1973) who studied the effects of THC as a hypnotic, testing a sample of 9 insomniacs. The same result - quickening of the sleep process - was found in non-insomniac subjects in a study by Gorelick et al (2013). A study into THC and cannabidinol use by Carlini & Cunha (1981) found that cannabis had both hypnotic and anti-epileptic effects on subjects. Taking either substance before sleep was found to significantly increase the overall length of sleep, although with some higher doses, the subjects reported 'hangover' type feelings the morning after, which were not reported in subjects administered with the lower dosages. Cannabis has also been found to increase the amount of time sleepers spend in deep (delta/slow-wave) sleep stages, the part of the sleep cycle in which restorative and reparative processes occur - see Feinberg et al (1975). A study into the effect of illicit recreational drugs on sleep by Schierenbeck et al (2008) confirmed this with empirical evidence. While deep sleep is increased with cannabis use, the one downside for dreamers is the fact that REM sleep is noticeably reduced, leading to a consequential loss of dreaming.

Strangely, cannabis use has also been found to have benefits for some sufferers of sleep apnea (25% of males and 9% of females with the condition). Sleep apnea has been linked to a number of other health problems, including diabetes and heart disease. Researchers are now trialling cannabis (in pill form, named 'dronabinol') as an alternative treatment to the disorder, which causes pauses in breathing during sleep. Initial studies by Prasad et al (2013) had positive results which they are hopeful will be replicated in a larger-scale research study.This is optimistic - currently many sufferers of sleep apnea leave their condition untreated and those who do seek medical help are encumbered by a sleep mask, which is uncomfortable and often disregarded as a long-term solution.

So, the main effect that cannabis use has on dreaming, is to reduce the amount of time the sleeper spends in REM (rapid eye movement) stages of sleep, the period in which most dreaming occurs. During the night, the sleeper will experience 4 stages of sleep, spending the longest periods in deep sleep and REM sleep.

1. Stage 1 - A very light stage of sleep which occurs at the beginning of sleep and lasts 5 - 10 minutes. The sleeper can be awakened very easily and if aroused, the sleeper will believe they were fully awake.
2. Stage 2 - A period of light sleep which lasts approximately 20 minutes as the body prepares itself for deep sleep. The temperature drops and the heart-rate slows.
3. Stage 3 (slow wave/deep sleep) - A deep period of sleep which lasts approximately 30 minutes. Delta brain waves are slow as blood flow is directed away from the brain and towards the muscles, restoring physical energy. If the sleeper is aroused during this stage of the sleep cycle, they usually feel disorientated and groggy.
4. Stage 4 (REM sleep) - The longest stage of sleep, during which most of our dreams occur. This stage of the sleep cycle is characterised by increased breathing and heart-rate and rapid eye movements. The paradoxical states of heightened brain activity (for dreaming) and muscle paralysis/immobilisation are also key features.

The REM and slow wave stages of the sleep cycle are closely interrelated; the longer you spend in deep sleep, the less REM sleep you experience If you become sleep deprived, the brain will automatically compensate for the previous lack of deep sleep, which again, lessens the amount of time spent in REM sleep. This is because the damaging effects of sleep deprivation are thought to be caused by a deficit in the restorative deep sleep, during which the body and brain heals and repairs itself from daily wear and tear. Using cannabis before bed has also been found to reduce the density of rapid eye movements in sleepers, a confirmed in a study by Lucidi et al (1996), although lower density of rapid eye movement has been linked to a more restful, relaxing sleep, so it is not all bad news! Most of the studies on cannabis and sleep have focused on the effects of THC, but in contrast, some research suggests that the other compounds in cannabis - namely, CBD - may interfere with the effects of THC and even promote wakefulness - see Nicholson et al (2003).

Regular cannabis smokers find that they experience an atypically high amount of REM sleep when they quit or take a break from cannabis use. The REM rebound effect leads to longer, denser amounts of REM sleep, during which many oneironauts or test subjects report extremely vivid, easily recalled dreams. The sleep distrurbances which occur during withdrawal from cannabis onset around 24 - 72 hours after cessation of cannabis use and may persist for up to 6 - 8 weeks afterwards, which is one positive aspect for oneironauts and dream explorers! However, the REM rebound effect is not unique to cannabis use; other substances which interfere with the sleep cycles - such as alcohol and medications - may also cause REM rebound, much the same way that sleep-deprived individuals undergo a deep-sleep rebound effect when they finally get to sleep. This is an amazing example of how the brain seeks to finely tune and balance the sleep cycles to ensure our wellbeing and health - and also points to the biological necessity of REM/dream sleep, which has been perceived by some, as being of secondary importance to deep sleep, because the latter tends to be 'prioritised' over the former, when an individual is deprived of sleep. Studies into the effect of substances on REM sleep and the REM rebound effect may shed new light on how the body and brain copes when deep sleep in nurtured and the sleeper is deprived of REM sleep only. This may help scientists discover the true nature of REM sleep and why it is so important to our emotional, mental and physical health. However, some research has indicated that spending more time in REM sleep may be linked to depression and other forms of mental imbalance. Because the brain is very active during REM sleep, it is likely that this stage in the sleep cycle is not responsible for rest or repair of the brain and that deprivation of REM sleep impacts little on memory or learning. 

Further, there have been indications that medical cannabis could be used to help treat those who suffer from nightmares or post-traumatic stress disorder. Clinical trials have confirmed that because cannabis interrupts REM sleep, synthetic cannabinoids may be successful in reducing nightmares, with 73% of subjects experiencing significant reduction or cessation.

All Sex & Violence: Freud's interpretation of dreams & evolutionary theory

A compelling theory which argues that Freudian Wish Fulfilment Theory can coexist with biological research into the physiological state of REM sleep. McNamara presents research which suggests that dream content is mostly violent or sexual and likely to influence waking behaviour. His explanation for REM sleep and dreaming is that it contributes to the process of mating and reproduction, consistent with Darwin's theory of sexual selection.

Patrick McNamara is Director at the Evolutionary Neurobehavior Laboratory at the Boston University School of Medicine. He has spent two decades analysing dream content in the hope that he might prove correct his hypothesis that sex forms the subtext of all dreams, reinstating Freud's debunked theory. McNamara, in his very recent article published in Aeon Magazine, states that from the offset he perceived Freud as a 'secular saint' who was 'willing to take an unbiased look at himself through the raw material of his dreams'. Freud's famous 'Irma's Injection Dream', which occurred on 23rd July 1895 and recorded and analysed in The Interpretation of Dreams (1900) was used as the basis for Freud's psychoanalytic technique of dream interpretation (see my previous article on 'Irma's Injection') and is regarded as the 'specimen dream' of psychoanalysis generally. McNamara argues that 'Irma's Injection' is clearly a sexual dream, a sexual wish fulfilment - the dream takes place at a party celebrating Freud's wife's birthday, but his attention is focused on Irma, whom he interpreted as representing a young widow he desired to treat. His friends, including Otto, were portrayed as male competitors. Further, the chemical formula for trimethylamine - the substance which Irma had been negligently injected with by Otto (causing a white patch in the back of her throat) appeared in bold type before Freud's eyes, alerting him to the cause of her discomfort in the dream. Freud's friend and colleague Wilhelm Fliess had referred to the substance as a 'product of sexual metabolism' found in semen. The connotation of 'injection' and the female throat - representative of the vagina - are also quite obvious in a sexual interpretation of the dream content. However, this interpretation has been heavily criticised by those who claim that psychoanalysis and Freudian dream interpretation is based on idiosyncratic associations which are open to endless alternative explanations.

By the time McNamara commenced his career into dream research, criticism of Freudian dream interpretation was full-blown - from 1953 onwards, after Nathaniel Kleitman (a physiologist at the University of Chicago) and his student, Eugene Aserinsky, discovered that dreaming occurred during REM sleep, Freud's theories of sexual wish fulfilment in dreaming were upended completely and discredited as mumbo-jumbo. A new cognitive-based approach to dream content emerged, replacing psychoanalytic theory, treating dreams as ethereal, disembodied products of a neutral information-processing and largely mechanistic brain. Researchers such as J Allan Hobson saw dreams as nothing more than fanciful ad hoc images caused by random neural impulses rippling from the brainstem, the engine of REM sleep. McNamara argues that the physical condition of REM sleep does not preclude Freudian theory - REM could coexist alongside Freud's theories that dreams have a deep unconscious meaning and purpose and some form of evolutionary function. In the late 1970s, whilst working in a Chicago detox centre, McNamara had a sudden and clear revelation: a elderly, ravaged alcoholic male whom he was washing suddenly leapt up with a full erection, lifted a metal table over his head and threw it at a wall, shouting expletives in a sing-song tone. McNamara was informed that the old man was suffering from delirium tremens as a result of alcohol withdrawal. The 'DTs' are characterised by an atypical transition state between REM and wakefulness and the enactment of dreams - which was what occurred with the old man to turn him from a frail invalid to a raging bull.

McNamara state that during REM sleep, males experience prominent erections, while in females the clitoris becomes engorged. Studies using functional magnetic resonance imaging have shown that the brain's reward circuits and centres are very active during REM. This lead McNamara to conclude that there must be some link between dreaming and sex.

During his academic career in neuroscience, McNamara gathered a large quantity of dream reports and noticed certain thematic patterns, becoming increasingly convinced that men and women dreamed drastically different types of dreams, with sex as a common theme. Often men were engaged in some form of violent or aggressive struggle or adventure, while women experienced dream scenarios were they would be communicating with friends. McNamara used the DreamBank.net resource for obtaining dream records - the site is managed by psychologists at the University of California at Santa Cruz, and contains over 20,000 dream reports and was able to find support for his hypothesis that male dreamers are more likely to experience dreams where they are physcially aggressive, while females tend to dream of subtlety denigrating other female competitors rather than physical acts of violence. After he became a Professor at Boston University in the mid-1990s, McNamara confirmed his observations in rigorous studies, which showed that men dream of other men more than they dream of women; and women dream about men and women equally. While male dreamers engage in physical violence against other men, women use verbal insults, rejections and exclusions. 

McNamara believed his research supported Freud's theory that all dreams are about wish fulfilment - i.e. sex. This explained why males dream of violence: in our evolutionary past, this was the way to access fertile females. Females engage in verbal aggression because discrediting competition by spreading adverse or negative gossip was a reproductive strategy. 

In one particular literature review, McNamara found ample evidence that sex hormones surge during REM sleep and dreaming. Prolactin (which enables lactation in females and stimulation of the testes in males) rises rapidly as sleep commences as peaks at 3 am - 5 am, the period during which REM predominates. Release of prolactin can be blocked by sleep deprivation. Similarly, oxytocin (linked to bonding during sex) and testosterone, both of which are linked to the sex drive, peak at 4 am. This correlates with the fMRI studies which show peak activation of the midbrain - especially the pleasure-seeking areas of the brain linked with sex and addictive behaviours such as drug use - occurs during REM sleep. 

However, establishing an incontrovertible link between REM sleep, dreaming and sexual wish fulfilment (under Freud's model) required more evidence. McNamara would need to correlate specific dreams with particular mating strategies in life. He found that the most reliable measure was 'attachment orientation'  - a quality associated with sexual and emotional intimacy. 

Current attachment theory holds that people fall into a few broad categories: (a) in a happy relationship (securely attached to their partner); (b) not in a relationship, but desperately wanting to be (preoccupied and anxious): (c) in an unhappy relationship (preoccupied or anxious); or (d) dismissive about relationships (avoidant). If dreaming represents wish fulfilment, then dream content, dream recall and dream sharing should be lower in those who are satisfied with their current attachment orientation i.e. securely attached, dismissive and avoidant; and higher in those who wish to change their status i.e. anxious/preoccupied. His Boston University study involved hundreds of voluntary subjects from all categories of attachment orientation. The coders who analysed the dreams recorded from the subjects were blind as to the purpose of the study. McNamara was surprised by the results of his study. He found those that were anxious/preoccupied were more likely to recall dreams than those who were securely attached. They took less time to reach REM periods during sleep and their dream content involved higher levels of aggressive and competitive behaviours than the other groups. Both the anxious/preoccupied and the securely attached recalled more dreams than the dismissive/avoidant groups. For McNamara this was the typical pattern predicted based on the theory that dreaming is directly related to long-term sexual and relationship strategies. The anxious/preoccupied subject is passionately interested in forging a relationship with a romantic or sexual target and therefore recalls vivid dreams with emotional content relating to intimacy, whereas the dismissive/avoidant subject suppresses the subconscious desire for sexual intimacy, which is reflected in the dream content. 

McNamara also decided to compare aggression in REM dreams with non-REM (NREM) dreams, which occur in even more shallow sleep states. If it transpired that high levels of aggression only occurred during REM dreams it would strengthen the case that links sex to this physiological state i,e. the hormone surges, activation of the brain's pleasure centres and the stimulation of the genitalia etc. Fifteen subjects were fitted with a 'nightcap' designed by sleep researcher Robert Stickgold at the Harvard Medical School. The nightcap was programmed to beep at random, waking subjects so that they could recall their dreams, during REM, NREM and daytime wakefulness. Coders then scored dream content according to aspects of aggression. Social interactions between men and women and men and men were more likely to be depicted in dreams than wake reports. Aggressive social interactions initiated by the dreamer were more frequent in REM dreams than NREM dreams or wake reports. Friendly interaction initiated by the dreamer was more likely to occur in NREM dreams than REM sleep. Subsequent analysis revealed that where the dreamer was male, targets of aggression could be reasonably interpreted as competition for a sexual or romantic mate. 

With finding from the US National Institutes of Health, McNamara was able to replicate the findings of this study in a fully-equipped sleep lab, using electroenchephalogram (EEG) technology to measure brainwaves, which added rigour and precision to the empirical results. Hundreds of college-age subjects were carefully selected and slept in the sleep lab for several nights.They were subjected to a series of specially balanced awakenings so that all subjects were given the opportunity to recall both REM and NREM dreams. This latter study confirmed the findings of the earlier one, but also revealed new compelling evidence. For example, in dreams involving aggression, the dreamer was the aggressor in 58% of REM dreams, but only 29% of NREM dreams. Where the dream involved friendly social interaction, the dreamer initiated the friendly behaviour in 71% of NREM dreams, but only 42% of REM dreams. In both studies the REM-NREM different was most marked in males and the target of aggression was were competitors relative to the dreamer. 

McNamara questions why humans are exposed to such risks present in REM sleep states if all dreams relate to sex. The REM sleep period is 'dangerous' in biological terms, because the major anti-gravity muscles of the body are paralysed or inhibited and the thermoregularity reflexes are suspended making it impossible to produce internal heat. REM sleep is also associated with intense automatic nervous system (ANS) storms or instabilities. The ANS regulates key physiological processes such as heartbeat - which is why heart attacks commonly occur in the early hours of the morning in the dream-rick REM sleep periods. To summarise, every 90 minutes during sleep we enter a dangerous period of 'twilight' during which our reward centres are activated and we are sexually stimulated, but partially paralysed so that we cannot take advantage of these activations. As key physiological functions of the body collapse, we are forced to 'watch' things which we know as 'dreams'. McNamara asks why evolution would expose us to such risky biological changes which leave us vulnerable to predation and unable to regulate our temperature which could lead to disease. An erratic ANS system presents further danger. If REM sleep has an evolutionary function it must be an essential one.

MxNamara found his answers in Charles Darwin's The Descent of Man and Selection in Relation to Sex (1871). Darwin's theory of natural selection concerns the evolution of new species by selection of traits that adapt to the environment across generations. However, his theory of sexual selection concerns the emergence of traits and behaviours that enhance the chance of finding a mate and reproducing. Darwin's theory of sexual selection addresses criticisms of his theory of evolution which argue that not all traits help a species to survive. Darwin's explanation was that the spectacular tail or the reindeer's elaborate antlers do indeed expose the species to predators, hinder the animal's movement and have high energy consumption, but many traits of sexually reproducing animals boost reproduction rather than survival in the environment. The peacock's tail acts as a marker of fitness and fertility, attracting peahens and the reindeer's antlers are a weapon to be used in aggressive combat with male competitors during mating season. The objective was to intimidate competitors so much they would give up the fight for the fertile females. The pressures of sexual selection made it an imperative that male species develop weapons and adornments, thus giving a reason why animals develop non-adaptive, costly traits.

McNamara applied Darwin's theory of sexual selection to REM sleep and dreaming. He drew on research into REM Behaviour Disorder, a condition by which the neurons which cause paralysis are destroyed , allowing dreamers to physically move during REM sleep and dreaming. Male dreamers with REM Behavioiur Disorder tend to dream that their partners are under threat or being attacked by other males and physically enact the dream, by defending themselves with actual violence whilst asleep. REM paralysis is therefore a form of evolutionary protection which prevents us from acting out our dreams.

There has been debate into the effect of REM sleep and dreaming on waking life behaviours. Dylan Selterman of the University of Maryland has addressed which topic directly, conducting  a study into couples. He asked the subjects, all of whom were in committed relationships, to record their dreams and daily activities for two weeks. Selterman found that dreaming about some form of romantic interaction with a target significantly predicted interactions and behaviours with others the following day, in waking life. If the dreamer dreamed of sexual intercourse with their partner, they tended to report more romantic or sexual intimacy the next day - but only if the relationship was going well. If the dreamer dreamed of conflict with a partner, greater conflict was experienced the next day.

McNamara states that these results appear to confirm the obvious - that dreams influence waking behaviours, but when you apply the theory of sexual selection to this common-sense interpretation, we are able to draw the conclusion that dreams prefer to influence sexual behaviours. This is McNamara's overall explanation for the purpose of dreaming.   

The material for this article was sourced from Patrick McNamara, 'How Sex Rules Our Dreams' Aeon Magazine (2014) and written by Tallulah La Ghash based on his research.