Question

Name two hypotheses that attempt to explain the biological function of sleep, and give research evidence for each.

Answer 1

Ans :

Hypothesis explaining biological function of sleep ;

1. Restorative theory :  

The Restorative Theory was put forward in 2006, during which a group of workers argued that sleep served as a behavioral state of the body to save energy by lowering our body metabolism.The workers sought to explain that the purpose of sleep was to reorganize and store information, arguing that the cortical neurons that are involved in memory and attentive learning needed to rest in sleep, especially during REM sleep. The workers noted that this probably explains why we feel mentally sharper after a good night's sleep, as compared to how we feel after staying awake all night long. Thus, in Restorative Theory it was hypothesized that REM sleep plays a vital role in memory retention and consolidation, removal of trivial or unwanted information, and storage of important data from memory, all taking place during REM sleep stage. The theory predicts that sleep helps replenish our stores of neurotransmitters, arguing that this is because most cortical neurons decrease their activity during sleep.

Another group of workers hypothesized that slow wave sleep also has some restorative effect, since it appears to be a period of rest for the brain. They noted that the brain areas that are very active during wakefulness show an increase in slow wave sleep.As it has been stated that sleep is generally a time of growth and repair, these workers also noted that there is a rise in certain growth hormones that have been shown to increase during period of slow wave sleep

Preservation theory :

In an overview, sleep was noted to be so essential that long periods of sleep deprivation eventually results in stress- related deaths. In the Preservation Theory it was stated that sleep (and the desire to sleep at night or under conditions resembling night) are the result of the evolutionary process to keep us away from trouble. Thus, the theory proposes that sleep is an adaptive behavior to keep us away from night and darkness when predator species enjoy advantage in vision and stealth. Workers further argued that over time, the “sleep when it is dark” and “work in the day light” behaviors were amplified by natural selection and are present in the brain neurochemistry.

Since the classical hypnotoxin experiments of Legendre and Pieron in 1910, the existence of some sleep-regulating substances was proposed, and a number of endogenous factors were actually listed. Most of the listed substances were prostaglandins or their synthesis inhibitors, and these factors were believed to be present in the cerebrospinal fluid. It was believed that these multiple endogenous factors are functionally linked, such that sleep regulation involves a complicated mutual interference mechanism among them. The time of that report heralded the period of more intense efforts in the search for a better understanding of the neurophysiologic factors in sleep.

Developmental theory :

Some group of workers proposed the Developmental Theory, during which they put forward the idea that sleep, especially the REM sleep, play important role in the development of the brain. In support of this proposal, the workers further observed that REM sleep is a major component of sleep for babies in utero and infants.

It was hypothesized that REM sleep activates the visual, motor and sensory areas of the brain. In the brain of babies, it is be lieved that REM sleep increases the ability of neurons to function properly and to make the correct connections. Observation from lamb fetuses through Plexiglas windows implanted on the uterine walls, showed that during REM sleep fetuses, as a result of not having air to breathe, nevertheless move their chest as if they were breathing. According to these workers, this suggests that REM sleep plays a role in preparing the infant on how to behave in the natural function even before they come out into the world