Researchers first recognized specific categories of sleep in the early 1950s by studying eye movements. Rapid eye movement (REM) sleep is vital to health, and usually occurs in cycles of 90 minutes. It is also linked to dreaming. Alzheimer’s Disease diminishes REM sleep, which may contribute to the irritability so often seen in advanced Alzheimer’s sufferers. Dreaming is recognized to be important to synthesizing daily experience, and conscious brain functioning.
Differences in Stages of Sleep
The two major types of sleep are Non-REM (categorized into four stages) and REM. The longer duration of sleep is Non-REM—and this accounts for approximately 80 percent of all time spent sleeping (according to the website of the University of Maryland Medical Center).
Non-rapid eye movement sleep (Non-REM sleep) occurs in four separate stages, with the first and second associated with light sleep—and the third and fourth stage termed “deep sleep”. During non-REM sleep, hormones are released that support the immune function. Intermittently, REM sleep occurs. This is when psychoneurologists believe the brain processes information through dreams. During REM sleep, muscles are completely relaxed. Researchers believe the loss of muscle tone functions to prevent sleeping people from acting out dreams.
Disorders of REM Sleep
In fatal familial insomnia (a rare and hereditary disorder), individuals develop a total inability to sleep. Following onset of symptoms, adrenal damage, body wasting, and subsequent death occurs within seven to 13 months. This rare condition provides evidence of how important sleep is to health.
Another rare condition is known as Rapid Eye Movement Behavioral Disorder (RBD), in which afflicted individuals attempt to act out their dreams. RBD is often associated with loud vocalizations, punching, sleep-walking, and a lack of awareness of such activities. Symptoms are not usually observed until over 40 years of age, and more typically in men than women (see: Boeve B. 1184:15, Ann N Y Acad Sci; 2010).
Parkinson’s Disease and Huntington’s Chorea are similarly accompanied in many sufferers by REM sleep disorders—as is Alzheimer’s Disease. In advanced Alzheimer’s cases, “sundown syndrome” occurs in which patients are apt to wander off at night. While the exact reason this frequently-observed syndrome occurs is unknown, some medical researchers believe it is related to development of RBD. Published clinical research has also suggested RBD affects individuals with Parkinson’s Disease and dementia associated with Lewy bodies in that it preceded symptoms of these two neurodegenerative diseases (see: Boeve B et al. 17:146, J Geriatr Psychiatry Neurol; 2004). This article also presented diagnostic criteria for RBD as determined by the American Academy of Sleep Medicine’s International Classification of Sleep Disorders, Diagnostic and Coding Manual.
How Dreams Enable Perception and Cognition
It is theorized by psychological researchers that dreams help human beings make sense of life’s occurrences. In turn, this enables an understanding of the relationship of the occurrence to the individual, and increases the ability to make decisions and cognitive judgments. Therefore, rapid eye movement (REM) sleep is vital to preserving cognitive brain processes and decision-making.