iPaulina

Several theories have been made; the first salient one is to conserve energy. We save one hundred calories per night by sleeping: our metabolic rate drops by 10%, the digestive system is less active, heart and breathing rates slow and, apart from the brain, the whole body slackens. The second theory is the evolutionary protection theory, also known as the inactivity theory, which claims that sleep is to avoid predators; for example, some animals hunt during the night and sleep during the day to avoid being spotted by predators. A flaw in this theory would be its failure to explain why sleep-deprived humans fall asleep during the day. The third theory is the restorative theory, which states that sleep allows the body to replete areas that were depleted throughout the day. Although this theory is endorsed by scientists’ findings of tissue growth, hormone releases, and protein synthesis, there is little evidence to suggest that the body undergoes more reparation during sleep than during rest or relaxation. The final and most prominent theory is the brain plasticity theory. During the day, the brain is saturated with information; according to this theory, sleep is an opportunity for this information to be processed in neural reorganisation and for memories to be stored.

The four stages of sleep: N1, N2, N3 and REM 

N1, N2, and N3 are all classified as NREM (non-rapid eye movement) sleep. N1 and N2 make up over half of someone’s sleep time and are considered ‘light sleep’, meaning that someone in these stages is easy to wake up. N3 is considered ‘deep sleep’; in this stage, predominant delta-wave brain activity has been observed via an electroencephalography (EEG) in the thalamus and cortex. In the thalamus, the delta-waves are synchronised with the reticular formation (a set of interconnected nuclei spanning from the base of the cranium to the midbrain). Delta waves release melatonin and DHEA, the youth hormone, called so because delta waves (needed for growth, repair, and the immune system) occur most in infants and decline as you get older. REM is the peak of our sleep cycle, and the three prior stages lead into this climax. We dream during both NREM and REM sleep, but the type and quality of our dreams vary.

What happens when we dream?

During REM sleep, the brain is highly active: there are many similarities between REM sleep activity and activity during waking hours. Using positron emission tomography (PET), it is possible to perform a study of cerebral physiological and biochemical processes. This has revealed that people experience temporary paralysis, where their arms and legs are disconnected from the cerebellum, so that they cannot act out their dreams. The reason for dreams is a very contentious subject but some would say that it serves as a ‘rehearsal,’ training your brain to know how to react in various situations that could arise when awake. Dreaming plunges you into a scenario that you have no control over (with the exception of lucid dreams) and tests your reaction. The part of the brain responsible for this is the amygdala, which regulates ‘fight or flight’ responses. However, others would say that instead of looking into potential future situations, dreaming reconsolidates past ones. It acts as a safe environment to reprocess upsetting memories or relive good ones that will ‘last a lifetime’; in other words, dreaming is a natural form of self-therapy.

Clémence (UIV)