Functions of Sleep
There are many unknowns about the physiological purpose of sleep. Despite of the progressive discoveries at the moment it is not easy to develop a unique theory about the functionality. Sleep is a necessary and unequivocal conduct and its deprivation causes death, but what is its true value? In recent decades, many theoretical explanations have been proposed about the function of sleep and looking for answers, converge disparate theories, that attempt to explain the ultimate goal of our need to sleep, but it is still insufficient to give a universally accepted explanation. There are three main functions attributed to the NREM sleep, that are articulated in separate theories: Energy Conservation, restoration (physical and neurological) and protection. As for the theory of REM sleep memory consolidation is the one, that has more followers among the authors of sleep theories.
Theory of energy conservation
The dream, according to this view, serve to conserve energy. Energy expenditure arising during the day should recover in the sleep state (sleep), when the body has low levels of oxygen consumption, decreased heart rate and decreased muscle tone (these physiological changes occur only during the NREM state) . These authors also note the decrease in body temperature that would result in energy savings. The nocturnal energy conservation would serve to offset the increased energy demand following the principles of homeostatic self-regulation. Proponents of this theory are in sleep similar to a previous state of hibernation.
The restorative function is based on the need to rehabilitate the body after the efforts made during the day. The approaches, that lead to theories defined restorative sleep as an essential condition to reestablish physical and brain activity after a period of wakefulness. Sleep as a physiological restoration period. This recovery combat the physical and neurological fatigue generated by the body during wakefulness. This line of thought used to favor the obvious cognitive impairments that occur after sleep deprivation, impaired mental performance, memory problems and changes in the mood state such as irritability and depression.
The point of view of the theory of protection provides a preventive approach. Raised with the same ultimate results restorative function, unlike this one, it argues that sleep is the preventive measure to preserve the body develops to the future day wear. There is not a later restoration wear but a prevention.
Theory of memory consolidation
REM sleep is related to the strengthening and consolidation of memory and in this direction are studies, that have detected increased activity in brain areas that handle memory and emotions towards the other stages ,where there is no mnéstica capability recording.
To understand how the creative process works, that many studies put in the REM phase, has been a constant desire of human beings. Recent scientific studies link the creative processes of great geniuses with theories developed in dreams. These investigations define the REM sleep stage as a time of conflict resolution. In this research, a recent article in PNAS shows, that REM sleep enhances creativity in a conflict resolution. To this study raises more or less correctly, that Paul McCartney composed his legendary song Yesterday while during sleep and like Dmitri Mendeleev has seen his famous periodic table of elements in dreams. This approach has been called the sleeping brain creativity.
The main theories discussed are complemented by other less impact with less experimental support. Behavioral theories or adaptive theories, that defend the dream as a way of adaptation to the environment to ensure survival like the theory of the integrity of the neuronal synaptical network, the thermoregulatorial theory and another group of theories, where sleep is the responsible processes of cerebral maturation, cerebral detoxification or the process of removing toxic substances. This great variety of theories and hypotheses, that attempt to explain the function or functions of sleep coexist in the same field of research, because they are not contradictory and their approaches are complementary. All the theories are interrelated and define sleep as a complex state requiring a multifunctional explanation to its functionality.