Sleep

Nathaniel Kleitman and William Dement discovered the cycles of sleep through which we pass about 4 to 5 times every night. Each cycle contains the five stages of sleep and lasts approximately 90 minutes.

The first stage of the sleep cycle is a light sleep that lasts for about 5 to 10 minutes.

During stage 1 sleep, brain activity slows by 50 percent and produces theta waves, which occur four to seven times per second.

Myoclonic jerks are sudden jerks of the body due to uncontrollable muscle contractions during stage 1 sleep.

Hypnagogic imagery is often experienced during stage 1 sleep, which involves jumbled dream-like visions that flicker throughout our consciousness.

Stage 2 sleep accommodates for about 65% of the sleep cycle, lasting 10 to 30 minutes. During this stage, brain waves slow down, heart rate and body temperature decreases, and muscles relax.

Sleep spindles are abrupt bursts of electrical activity of 12 to 14 cycles per second that occur during stage 2 sleep.

During stage 2 sleep, sudden rising and falling of waves called K-complexes occasionally occur.

Stages 3 and 4 sleep are conceptualized as a single stage of sleep which lasts for about 25% of the sleep cycle for adults and 40% for children. These stages contain the deep sleep that is required in order to feel well rested.

During the deep sleep of stages 3 and 4, the brain experiences delta waves, which occur at one to two cycles per second.

Stages 3 and 4, as well as stages 1 and 2, are often referred to as non-REM sleep. The brain is less active than REM sleep, but dreams are still possible; 43 percent of non-REM periods generate dream reports.

Stage 5 is the final stage of the sleep cycle which lasts for about 15 minutes in earlier cycles and up to an hour during later cycles. During this stage, the brain experiences high frequency, low-amplitude waves, and heart rate and blood pressure increase.

REM sleep refers to rapid eye movements which occur during stage 5 of the sleep cycle. Vivid dreaming takes place during REM sleep.

A dream is the experience of images and sensations in the mind while asleep.

The activation-synthesis theory of dreaming presents that dreams are a result of the forebrain attempting to interpret meaningless brain activity from the pons.

Alan Hobson describes protoconsciousness as a primary state of brain organization that is present while dreaming, with which raw emotions and perceptions are dominant.

The neurocognitive theory of dreaming infers that dreams are products of cognitive and visuospatial abilities.

Apart of the neurocognitive theory where there is continuity between waking up and sleeping. This hypothesis also helps professionals distinguish dreams of people with hearing problems and disabilities.

Mark Solms' theory of dreaming claims that dreams are driven by the motivational and emotional control centres of the forebrain while activity in the prefrontal cortex is reduced. This results in vivid and emotional dreams that are logically incoherent.

Sigmund Freud's theory of dreams presents the belief that dreams represent disguised wishes that require interpretation.

In his book, The Interpretation of Dreams, Freud defines dream-work as the unconscious ciphering of sexual and aggressive impulses into meaningful symbols.

Freud describes dreams as the "Guardians of sleep" which suggests that dreams are a visual satisfaction that impacts the ID's desires.

Wish fulfilment refers to the symbols created by dream works, which represent how we wish things could be.

Lucid dreaming refers to the state of being aware that one is in a dream. This phenomenon occurs when one's consciousness features both waking and REM sleep, during which the individual can control the outcome of their dreams.

Sleep disorders interfere with the quality and amount of sleep one receives, which can result in distress during daytime activities.

Insomnia is a sleep disorder that involves difficulty falling, returning, and remaining asleep. Insomnia is often present in individuals with depression and medical conditions, and can be a result of stress, illness, and irregular sleeping patterns.

Narcolepsy is a sleep disorder that provokes sudden, unpredictable episodes of sleep that can last from a few seconds to an hour.

Sleep Apnea is a sleep disorder in which blockage of the airway causes difficulty breathing, resulting in snoring and being awakened many times throughout the night. While individuals with sleep apnea are often unaware of the awakenings, the lack of sleep and oxygen can lead to medical problems and an increased risk of death.

Night terrors, a generally harmless sleep disorder most common in children, refer to episodes of thrashing about while screaming, crying, and perspiring before falling back to sleep.

The sleep disorder of sleep walking involves a person acting awake while fully asleep. Sleep walking is most common in children, but occurs in 4 to 5 percent of adults.