One of the more intriguing aspects of human behavior comes packaged in an extremely natural and habitual act — sleep. Most of us take this routine of sleeping as part of the day, and slide in and out of it rhythmically, systematically. When we do, though, our bodies and minds enter this realm of unknown — theoretically, a passive state of rest for the body and mind. However, due to the many subtle and spontaneous reactions in physical and mental functioning, experts now term sleep as a dynamic rather than a passive state of being.

Sleep follows a circadian rhythm that is regulated by many factors such as light (in the external environment), fatigue and stress (within the body and mind) and the production of certain hormones such as adenosine and melatonin. During daytime, the presence of sunlight triggers production of hormones like cortisol and adenosine, which promote alertness and wakefulness. As recedes and darkness sets in, the eyes register the change in quality of light, transfer the message to the brain cortex — and this stimulates production of melatonin, which promotes drowsiness and tiredness. Interestingly, the optimal concentration of these hormones through the day and night varies significantly from person to person. This may explain why some people prefer to stay up and wake up late, while others prefer to sleep and wake early. Newborns usually spend 14-18 hours in a day sleeping, and this decreases to 8 hours a day in adulthood.

Sleep is mainly comprised of two stages — the non-rapid eye movement (NREM) and the rapid eye movement (REM) phases. The former is a state of lighter sleep, while the latter is a deeper state. The NREM phase is followed by the REM state, and this cyclical progression occurs about 4 or 5 times in each 8-hour sleep period. As the name suggests, there is no eye movement in the NREM phase, and the overall muscle tone is maintained. This is the stage that is achieved just before the act of falling asleep and also precedes the act of waking up. The REM phase is characterized by complete relaxation in muscle tone, and cessation of physical activity. However, the brain becomes much more active during the REM phase; the thalamus, reticular nuclei and hypothalamus in the brain especially show increased activity (as observed by studies recording an increase in blood flow to these areas). Dreams commonly occur at this stage of sleep.

This is where strict definitions do not hold good, where rigid theories don’t always hold true. When we are dreaming, there is a certain part of our mind and being which is aware and conscious, yet some other parts of the brain that are completely at rest. Experts suggest that various types of dreams exist, that range form the dreamer not being in his or her own dream (dreams of childhood) to one where the dreamer is actively reflecting upon the ongoing dream and making deductions and judgments on the events happening in the dream (lucid dreams). This is an interesting lead to the contemplation about the distinction between dreams and reality.

The more I ponder over this, the more baffled I get. The contrast in this state of sleep is amazing — while the body recharges, the mind is replete with huge amounts of activity. Mental activity, when it occurs during the day, tires and stresses the human mind. Yet, one wakes up refreshed even after a night of sleep filled with dreams. Advances in funded sleep studies, establishment of numerous sleep analysis centers across the country have revealed a tremendous amount of information about the state of sleeping; but many aspects of sleep still remain a mystery.

Related Articles

• Yoga and Paradoxical Wakefulness
• Go to Bed Angry!
• Sleep Is Important for Next Day Memory Formation
• The Sad Implications of Sunday Sleep Problems
• Sleep and Obesity – A New Link