Understanding the stages of sleep

While sleep is an element necessary for maintaining optimal health, ever wondered what happens when you fall asleep? You may sleep for six to seven hours or seven to nine hours a day, but what goes on in the brain and body during a sleep session is an aspect that scientists are actively researching.In the first few sleep cycle stages, the mind progresses from wakefulness and moves on to light sleep and finally, deep sleep. It is called non-rapid eye movement sleep (NREM). In REM (rapid eye movement), the brain is aroused with activities.

An electroencephalogram (EEG) is used to measure brainwave frequency amplitudes and differentiate various sleep stages.

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Stage 1

In this stage of sleep, a transition takes place – from being awake to entering sleep. The brainwave frequency in the EEG is slower when compared to that of a wakeful state, but this is the lightest one in the sleep cycle. Skeletal muscles show the presence of muscle tone (muscle movements). Breathing continues at a regular rate and slow eye movements continue.

Stage 2

In this stage, eye movements stop and brainwaves slow down. There is a burst of rapid waves at irregular intervals called ‘sleep spindles.’ In this stage, sleep has intensified and if a person is woken up by a stimulus, they realise that they have been disturbed by an external force.

Stage 3 and 4 (slow-wave sleep/deep sleep)

In these stages, brain waves slow down further into what is termed as ‘delta waves’ which are interspersed with occasional faster waves as you enter deep sleep. Body temperature drops and so do heart rate, blood pressure and muscle tone. Eye movements are absent during deep sleep and this is the deepest and most restorative phase of sleep.

REM Sleep

REM sleep is associated with various activities right from brain development to emotional processing. Here, a person’s eyes move rapidly behind the closed eyelids, leading to the heart rate going up, brain waves slowing down and breathing becoming irregular. It is almost like a wakeful state, but with the eyes closed. People experience a temporary loss of muscle tone in this stage.

Sleep experts explain the stages of sleep

“There are four to five stages of sleep. The light stage of sleep (stages 1 and 2) is when our heart rate and body temperature drop. This is the stage when procedural and declarative memory consolidation happens,” explains Dr Yishan Xu, clinical psychologist and an expert in behavioural sleep medicine, Los Altos, California, USA. Declarative memory or explicit memory is where facts and events are stored. Rapid learning and conscious recall are hallmarks of this memory. Procedural memory or implicit memory is related to skill development and learning. These memories work automatically as they function without conscious involvement.

Dr Xu adds, “stages 3 and 4 are important for children and teens to grow, as the body during these stages of sleep releases growth hormones. But as we age, less time is spent in these stages. This is the stage when the body repairs and regrows tissues. The muscles and bones are built and the immune system is strengthened. This is also the stage when sleepwalking, night terrors and bedwetting occur.”

What happens during REM?

This is the stage of sleep where the brain is aroused with mental activities; a person’s voluntary muscles become immobilised and this stage begins after 90 minutes after falling asleep. This is also the stage where dreams occur. Temporary muscle paralysis will help a person from acting out the dreams. There are times when people can wake up during REM, but they may not remember these moments.

Dr Vivek Anand Padegal, director of pulmonary and sleep medicine, Fortis Hospital, Bengaluru and diplomate in sleep medicine from the American Board of Sleep Medicine, says that it is important to get seven to nine hours of sleep a night at a stretch. “It is better than getting fragmented and disturbed sleep at different times during the day, even if it is more in length and quantity. REM sleep is very important but getting more or too little of it is disadvantageous and bad for health. I would suggest healthy sleep hygiene and necessary lifestyle changes to get the most out of sleep,” he says.

Dr Xu says that if the normal stages of sleep are disturbed, our bodies will miss opportunities to relax and recover. “The impacts of it will be felt the next day – (a person will be) groggy, fatigued, lacking in focus as well as concentration, and prone to impaired or impulsive decision-making,” says Dr Xu.

How do sleep stages work in babies?

For the first four to six months after birth, the circadian rhythm (also called the body clock) isn’t fully developed and in effect, babies might sleep more during the daytime; they could be wide awake at night or vice versa, which could be puzzling to new moms and dads.

“A baby goes through different depths and stages of sleep. A neonate (newborn baby) might sleep 16-18 hours a day which translates to six to eight sleep cycles. Sleep stages are different in babies: it may be categorised as quiet sleep, active sleep and indeterminate sleep,” says Dr Sreedhara MS, consultant neonatology and paediatrics, Rainbow Children’s Hospital, Bengaluru.

He says that through the EEG, experts can analyse how good or bad the sleep is. They determine how regular a baby’s breaths are, how deep the sleep is and how easy is it to awaken her/him. They also monitor body movements and vocal sounds.

Ways to sleep well

Dr Yishan Xu recommends four steps to getting better sleep:

Stick to the same wake-up time

It is more important to wake up at the same time every day than it is to go to bed at a regular hour.

Sleep is more important than work

Research shows that even going to bed 15 minutes earlier is beneficial as that little extra sleep will help you perform better the next day.

Manage sleep anxiety better

Don’t worry too much about disturbances; don’t force your sleep. If you are not sleepy, relax. You fall asleep naturally when you are less worried.

Quality sleep is better than sleeping long hours

Even if you sleep for fewer hours, you still go through these sleep stages and the body will get what it needs for basic functioning. High-quality five hours of sleep is much better than fragmented or disturbed eight hours of sleep. Improve sleep quality first. Then you can slowly expand your sleep quantity.