Sleep Restoration

The multiple theories proposed to explain the functions of sleep reflect the current incomplete understanding of the subject.

It is likely that sleeping as a function evolved to fulfill some primeval function, but has taken over multiple functions over time as organisms have evolved. An analogy would be that to the larynx, which performs multiple functions, such as controlling the passage of food and air, phonation for communicating and social purposes, etc. These are all functions of the larynx, but just one of them likely represents the original function. Some of the many proposed functions of sleep are as follows:

Wound healing has been shown to be affected by sleep. A study conducted by Gumustekin et al. in 2004 shows sleep deprivation hindering the healing of burns on rats.

A study by Bonnet and Arand in 2003 indicates that sleep affects metabolism. Comparing normal human sleepers and sleepers with sleep state misperception insomnia, where patients complain of poor sleep but have normal sleep by electroencephalographic (EEG) criteria, the researchers found significantly greater metabolism values for the normal sleepers.

It has yet to be clearly proven that sleep duration affects somatic growth. One study by Jenni et al in 2007 recorded growth, height and weight, as correlated to parent-reported time-in-bed in 305 children over a period of nine years (age 1-10). It was found that "the variation of sleep duration among children does not seem to have an effect on growth". It has been shown that sleep, more specifically slow-wave sleep (SWS), does affect growth hormone levels in adult men. During eight hours sleep, Van Cauter, Leproult, and Plat found that the men with a high percentage of SWS (average 24%) also had high growth hormone secretion, while subjects with a low percentage of SWS (average 9%) had low growth hormone secretion.

There are multiple arguments supporting the restorative function of sleep. We feel rested after sleeping, and it is natural to assume that this is the basic purpose of sleep. Overall metabolic rate goes down during sleep and certain anabolic hormones such as growth hormones as mentioned above are secreted preferentially during sleep. Sleep among species is, in general, inversely related to the animal size and basal metabolic rate. Rats with a very high basal metabolic rate sleep for up to 14 hours a day whereas elephants and giraffes with lower BMRs sleep only 3-4 hours per day.

Energy conservation could as well have been accomplished by resting quiescent without shutting off the organism from the environment, potentially a dangerous situation. A sedentary non-sleeping animal is more likely to survive predators, while still preserving energy. Sleep therefore does something else other than conserving energy. Most interestingly, hibernating animals that wake up from hibernation go into rebound sleep because of lack of sleep during the hibernation period. They are definitely well rested and are conserving energy during hibernation, but need sleep for something else. Rats kept awake indefinitely develop skin lesions, hyperphagia, loss of body mass, hypthermia and eventually septicemia and death.

Anabolic/catabolic

Non-REM sleep may be an anabolic state marked by physiological processes of growth and rejuvenation of the organism's immune, nervous, muscular, and skeletal systems (with some exceptions). Wakefulness may perhaps be viewed as a cyclical, temporary, hyperactive catabolic state state during which the organism acquires nourishment and reproduces.

Ontogenesis

According to the ontogenetic hypothesis of REM sleep, the activity occurring during neonatal REM sleep (or active sleep) seems to be particularly important to the developing organism (Marks et al., 1995). Studies investigating the effects of deprivation of active sleep have shown that deprivation early in life can result in behavioral problems, permanent sleep disruption, decreased brain mass (Mirmiran et al. 1983), and an abnormal amount of neuronal cell death (Morrissey, Duntley & Anch, 2004).

REM sleep appears to be important for development of the brain. REM sleep occupies majority of time of sleep of infants, which spend most of their time sleeping. Among different species, the more immature the baby is born, the more time it spends in REM sleep. Proponents also suggest that REM-induced muscle inhibition in the presence of brain activation exists to allow brain development by activating the synapses yet without any motor consequences which may get the infant into trouble. Additionally, REM deprivation results in developmental abnormalities later in life.   However, this does not explain why older adults still need REM sleep. Aquatic mammal infants do not have REM sleep in infancy REM sleep in those animals increases as they age.

Animal studies have demonstrated that sleep is essential for survival. Consider studies that have been performed with laboratory rats. While these animals will normally live for two to three years, rats deprived of REM sleep survive an average of only five months. Rats deprived of all sleep survive only about three weeks.  In humans, extreme sleep deprivation can cause an apparent state of paranoia and hallucinations in otherwise healthy individuals. However, despite identifying several physiological changes that occur in the brain and body during sleep, scientists still do not fully understand the functions of sleep. Many hypotheses have been advanced to explain the role of this necessary and natural behavior.  The following examples highlight several of these theories:

The theory of restoration recognizes the need for an organism to replenish its energy stores and generally repair itself after a period of energy consumption and breakdown (wakefulness). The brain remains active during sleep, and the low metabolic rate characteristic of sleep is thought to be conducive to biosynthetic reactions. There is little, if any, evidence that more repairs occur during sleep than during rest or relaxed wakefulness. In fact, whole-body protein synthesis decreases during sleep, which is consistent with sleep being a period of overnight fasting.

Sleep is one of nature’s greatest inventions and blessings of life. It is a periodic rest of the body, which is absolutely essential for its efficient functioning. It has been called "most cheering restorative of tired bodies."  Sleep is an indispensable condition and is absolutely necessary for the recuperation of energy. We go to bed fatigued and get up refreshed. Sleep repairs the wear and tear of the body and mind incurred during waking hours. Nothing is so restorative to the nerves as sound and uninterrupted sleep. Sleep is thus a vital element throughout the life of all mammals and most other animals and birds in the animal kingdom.  It is a basic need in man’s mental as well as physical life.

During sleep most of the functions of the body are carried on at the lowest level possible in health. Heat production is from 10 to 15 per cent below the basal level. The mechanism regulating the body temperature is less sensitive than in the waking state and are depressed by 0.5 to 1.0 degree F. The rate of the heart is reduced by 10 to 30 beats per minute and a decline in blood pressure of about 20 mm occurs in quiet restful sleep. The urine volume is considerably reduced, but its concentration in solids is increased. The tone of all the skeletal muscles is lessened. The eyes are usually rolled upward and the pupils constricted. Loss of sleep exerts serious detrimental effects upon the nervous system.

Long periods of wakefulness may cause profound psychological changes such as loss of memory, irritability, hallucination and even schizophrenic manifestations. During the last World War, prisoners in Nazi concentration camps who were kept awake for days by strong lights and blaring wireless sets, collapsed.

Excerpts taken from this article are licensed under the GNU Free Documentation License. They use material from Wikipedia topics "Lucid Dream" and/or "Sleep".