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All living organisms have a rest-activity cycle. The need for rest is essential for life and if it is prevented in animals, as shown experimentally, life-expectancy is drastically shortened. The need to sleep is unavoidable. This is unlike eating, for example, where an individual can starve himself to the point of death.
Studies of sleep have implicated certain areas in the brain that regulate the sleep cycle, which has enabled researchers to categorize the sleep cycle into specific stages. Knowledge of what occurs during the sleep cycle stages is helpful for understanding the consequences of .
Human sleep has been categorized into two distinct states: rapid eye movement (REM) and non-rapid eye movement (NREM). The flow between the two states during sleep is defined by the electrical pattern of the brain as recorded by electroencephalography (EEG) - a test where electrodes are strategically placed on the scalp to record the electrical activity of the brain. NREM sleep is the first type of sleep during the cycle and generally is characterized by a "slowing" of the body. NREM sleep is divided into four stages and the stages are separated by distinct EEG patterns. Stage 1 sleep is the transitional stage between wakefulness and sleep, and lasts about five minutes. Stage 2 has characteristic EEG patterns that differentiate it from stages 1 and 3, and it lasts for approximately forty to sixty minutes. Stage 3 and 4 sleep have similar EEG patterns and last for about twenty to thirty minutes together. These stages are important because they are required to reduce the need for sleep.
The EEG pattern during REM sleep resembles the waking state. Physically, the limb muscles become temporarily paralyzed, blood pressure rises, breathing becomes labored and the eyes move about rapidly. (Hence the name rapid eye movement.) Psychologically, this is the stage of dreams. Much has been written on the meaning of dreams: Sigmund Freud believed that dreams were a portal into the unconsciousness and a means by which to express primitive emotions that were unacceptable to address in the consciousness, and Carl Jung spent most of his career describing a framework into which the symbols of dreams could be understood. (To note, recent neuroimaging studies have supported Freud's theory at an anatomical level. During dreams, there is high activity in areas of the brain associated with emotions and motivation.) However, from a strictly scientific viewpoint that has a worldwide consensus, the "why" of dreams is unknown. What has been repeatedly shown is that REM sleep is needed for new learning. When an individual is deprived of REM sleep, they cannot recall newly learned material.
A typical sleep cycle averages an hour and a half, and there are four to six cycles per night in an average night's sleep of eight hours. The sleep cycle is not static and changes as the night progresses. The percent of Stage 3 and 4 sleep is highest in the beginning and decreases throughout the night, while REM periods increase in length throughout the night.
The sleep cycle is also dependent on age. Infants and children sleep more and spend more of sleep in REM. Also, as we age, the amount of Stage 3 and 4 sleep decreases, and the sleep cycle becomes fragmented and has less continuity. The need for sleep is the same, but adherence to a nightly schedule is not as strong as in the young. Thus, there is a higher frequency of daytime naps in the elderly.
There are two processes in the body that determine when it is time to sleep and they are independent of each other. The first process is called homeostasis - the medical term for equilibrium or balance. This is simply that the likelihood of sleep increases as the period of wakefulness increases. No matter how much one may try, if one stays up long enough, sleep will occur. The second is called circadian (Latin for about the day) rhythm, commonly referred to as the "biological clock." This is a clock in the body that is set by the light of day and the dark of night. The clock is located in a specific area of the brain called the suprachiasmatic nucleus, and it receives input from the retina of the eyes. Without this input, the clock will run a rhythm of 24.5 to 25 hours. This extra length poses a problem to blind individuals. Patients with total blindness have a sleep cycle that lasts a little bit longer each day and they usually have to take medication to adjust their cycle to the outside day and night.
Insomnia is the inability to fall asleep or remain sleeping for an adequate length of time. It is a very common problem, and an estimated 60 million Americans suffer from insomnia annually. Physicians use insomnia as a clue to look for an underlying cause. Anxiety, depression, drug use or a wide variety of medical conditions can cause insomnia. When the underlying cause is treated, the insomnia usually resolves. If an underlying cause is not found, the insomnia is "primary." And, there are a number of successful maneuvers to treat primary insomnia.
Jet lag is the fatigue, daytime sleepiness, insomnia, clumsiness, and lack of concentration that accompanies travelers after they have traveled through multiple time zones. The cause of jet lag is the failure of the biological clock to adjust quickly to the light-dark cycle of the new environment. Naturally, the body can adjust its circadian rhythm at the pace of around 1 hour per day. Jet travel overwhelms the body's ability to shift the sleep cycle and thus symptoms of insomnia result. There is no specific treatment that can override the circadian rhythm, yet there are maneuvers that facilitate the re-setting of circadian rhythm to the new time zone.
Narcolepsy is a disease that affects about 0.05% of the population, which makes it about as common as multiple sclerosis. Narcolepsy is Greek for "stupor attack" and it consists of immediate episodes of sleep that can be associated with loss of muscle tone. Patients also complain of excessive daytime sleepiness, even though they may be getting adequate sleep during the night. The sleep of narcolepsy resembles REM sleep and is associated with increased respirations and eye movements. If untreated, a patient usually has from 2 to 6 episodes per day that last from seconds to more than 30 minutes. The cause of narcolepsy is unknown, however it seems to run in families. Narcolepsy also occurs primarily in males and symptoms usually start in adolescence. Narcolepsy cannot be cured, however the symptoms can be treated.
Nightmares are common and 80 % of the adult population occasionally has them. The incidence is even higher in children. Basically, nightmares are dreams (and hence occur during REM sleep) in which the individual or someone close to the individual is put in some deadly or humiliating situation. In some cases the nightmare can disrupt sleep and the person can awake. Once the person awakes, he or she feels relief due to the realization that the person "was only dreaming." Why people have nightmares is unknown, but the frequency of nightmares increases with stress as well as withdrawal from alcohol and drugs. People typically do not seek treatment for nightmares as their frequency is usually low and they are tolerable. If an individual has persistent nightmares, his or her physician will look for an underlying cause to treat, such as anxiety or substance abuse.
About five percent of children, experience night terrors, though adults can also have them. A night terror is an abrupt awakening from sleep that is characterized by screaming, sweating, motor movements, and fear. While this can resemble a person waking from a nightmare, a night terror is different. Night terrors occur during stage 4 sleep and are not the result of dreams. Consequently, the person has no recollection of the terror when he or she awakens. Since they occur in stage 4, night terrors usually occur during the first half of the night. Most childhood cases resolve. Night terrors in adulthood are usually associated with a concurrent psychiatric diagnosis such as depression or posttraumatic stress disorder. However, an individual may have night terrors without an accompanying psychiatric condition.
Restless Legs Syndrome
Restless legs syndrome (RLS) is an unpleasant sensation of crawling or prickling in the legs that occurs at rest. The sensation is relieved after movement. RLS presents as constant leg movement during the day and insomnia at night (Patients have difficulty falling asleep due to their need to move their legs.) The condition was first described in the 1600s and study has shown that it affects about 5 % of the population, with the elderly having the most severe cases. The cause of RLS is unknown; however some conditions are associated with it, such as iron deficiency and pregnancy. Also, there may be a genetic component to RLS. Twenty-five to fifty percent of RLS patients have a family history of RLS. Treatment of RLS is directed at the underlying cause or exacerbating factor. In addition, there are interventions directed specifically at decreasing the urge to move one's leg.
Sleep apnea (Greek for "without wind") is a disorder of breathing that is a common cause of insomnia. Sleep apnea is a disruption of breathing that breaks up the sleep cycle and prevents a normal night of sleep. The majority of sleep apnea cases are due to an obstruction of the airway. This usually happens when the muscles of the respiratory system relax during sleep. Normally, this is not a problem. However, this may become a problem in certain patients with a predisposition for sleep apnea. Patients with obstructive sleep apnea are usually overweight and have fat tissue that obstructs the airway, are older and therefore more prone to having a loss of respiratory muscle tone, or have a small receding jaw or short neck that allows the tongue to obstruct the airway. Obstructive sleep apnea (OSA) is a common problem and affects approximately 4% of middle-aged adults. Patients with OSA are usually not awoken during the night and are not aware of the problem. They usually complain of insomnia, daytime tiredness, irritability, and depression. However, their bedfellows describe their partners as experiencing bouts of snoring, restlessness, and occasionally "choking" during the night. OSA is typically addressed by interventions alleviating the obstruction.
Somnambulism, more commonly known as sleepwalking, is an extremely dangerous disorder of sleep. Somnambulism is a disturbance of deep sleep (stages 3 and 4) in which the normal relaxation of the limb muscles is disrupted and the sufferer can get out of bed and walk around. Since somnambulism occurs in stages 3 and 4, most instances occur during the beginning of the night. The person suffering from this would still be asleep during these activities and would not be aware of his or her actions. This can be very dangerous because an individual may seriously hurt himself or herself: for example, fall down stairs or walk through glass. Fortunately, the majority of cases occur in children and most of the sleepwalkers do not actually walk. Instead they may make repetitive movements, e.g., sitting up or pulling at their pajamas. Most cases of somnambulism resolve by adolescence, however some arise or continue into adulthood. Somnambulism is usually addressed by maneuvers promoting a normal sleep cycle and by safety measures to prevent injury for residual episodes.top of page