What are the Sleep Cycle, and is it Important in Sleep Disorders?
Sleep is a natural, recurring state of body and brain, characterized by altered awareness, primarily reduced sensory activity, decreased motor activity and inhibition of most non-voluntary muscles during REM sleep, the stage in which dream sleep begins. Sleep is most typically noted as periods of time during which an individual’s body remains awake and alert, although it may be partially awake and sometimes aware of external stimuli. At various times during sleep, the body may react to stimuli with arousal and/or sleep. Various theories suggest that sleep is needed to repair and maintain normal brain function and plasticity. Others believe that sleep is necessary for the regeneration of cellular structure.
There are many factors that can determine when an individual needs to sleep. These include: The timing of light and darkness; environmental stress, such as sleep deprivation or the presence of a physical illness; an inability to fall asleep within a reasonable amount of time after waking; and an inability to stay asleep during the night. A person who awaken at a normal hour but do not go to sleep and wake up at the same time every day tends to be highly creative and perceptive, but is unable to recall events that happened during the night. People who regularly skip sleep are often highly irritable and moody. The tendency to sleep less than normal also makes people more sluggish, confused and impulsive.
Children have a habit of sleeping through the night, but they eventually learn to sleep through the day. Children require nine hours of sleep each night to maintain normal development. An eight-hour sleep schedule is more common among children than adults, and requires only four hours of sleep during the night. Rapid eye movement sleep (REMS) is a neurological process during which the eyes move rapidly from one location in the brain to another during sleep.
When the body is in REM sleep or dreaming, it enters what is called the dream stage. During this time, the brain is relatively inactive, enabling it to be susceptible to implanted hypnotic suggestions. The most common cause of dreams is stress. As a result, it is possible to program the brain to ignore stressful stimuli such as a dream, thereby promoting good sleep and waking up rested and alert the next day. Neurofeedback, or biofeedback, has been used to teach people to recognize when they are entering a dream state and then to use positive affirmations to bypass the stress-inducing thought patterns during the dream stage.
Although the length of the average sleep cycle has not been fully understood, there is evidence that humans tend to sleep for about seven hours, including a few short naps during the night. About two-thirds of the total sleep time is spent in the REM (Rapid Eye Movement) stage of sleep, which is thought to be important for determining arousals and REM sleep. Other studies indicate that sleep duration is largely influenced by the amount of physical activity during the previous day.
Babies, like all other animals, spend most of their sleep in the REM stage. In the early days of the study, it was believed that REM sleep was primarily the stage when new memories were formed. Later researchers have indicated that, at least in adults, the main determinant of REM sleep is not necessarily the presence or absence of a distinct memory. Instead, it appears that REM sleep contributes to the accumulation of neurofibrillary protein, which accumulates in the cerebral cortex, particularly in the periaqueductal grey matter. This protein is thought to contribute to the formation of memories and can even act as a protective measure against Alzheimer’s disease.