Everyone does it. Everyone suffers if we don’t do it. Sleeping. We spend a whole third of our lives sleeping (or we’re supposed to) and yet… we don’t understand it. Getting a proper amount of shut-eye is essential for normal brain development. Sleep deprivation affects all of our cognitive skills, from memory to innovation and ideas. Sleep is a vast, integral and unavoidable portion of our life, and while we can record what happens during sleep, and what happens when we deprive ourselves of it, scientists still do not know why we conk out.
As the day wears on we become more tired, and thus it would make sense that our body would need to rest, recuperate, and save energy by shutting down for around 8 hours. However, sleeping that long uses the same amount of energy as being awake for 8 hours, give or take about 50 kCal –the equivalent of a piece of toast. Energy saving is not the solution.
As we fall asleep, our body and brain goes through the famous REM (rapid eye movement) sleep, as well as 4 stages of non REM sleep – light sleep, true sleep, and two stages of deep sleep. Light sleep is that point where you are only half asleep, some people twitch slightly, and you can be awoken quite easily. True sleep begins about 10 minutes after light sleep does, and our heart and breathing rates slow down over the course of 20 minute blocks. True sleep makes up the largest proportion of human sleep. During deep sleep our heart and breathing rates are at their lowest, and in the fourth stage we have limited muscle activity and rhythmic breathing. If woken during deep sleep, people do not adjust quickly or well to their sudden consciousness, remaining groggy or disorientated for minutes afterwards.
Humans have from 3 to 5 REM periods per night, during which the brain is very active and we have dreams and nightmares. Brain activity during REM resembles wakeful brain activity more closely than it does during non-REM sleep. Possibly to prevent us acting out our dreams, most of our muscles are effectively paralysed during REM. Breathing rate and blood pressure rise, as if the body were active. If we are woken during this stage, we are much more likely to remember our dreams.
People average anywhere from 5 to 11 hours of sleep per night, and there is some debate about what the amount is, despite the folk wisdom of ‘8 hours’. If you ask Jim Horne from Loughborough University’s Sleep Research Centre, “The amount of sleep we require is what we need not to be sleepy in the daytime.” The world record for longest period without sleep that any human has maintained without stimulants, was set by Randy Gardener in 1965: 11 days. After 4 days he started to hallucinate, then believed he was a famous footballer, however he maintained remarkable functionality as the study went on and reportedly could still beat the scientists at pinball.
Though we remain confused about the origins of sleep, we do know that it is pretty much universal among animal species. From humans to snakes, to way back down the chain of evolution and invertebrates like jellyfish, nearly all animals have a regular sleep, or sleep-like state, and their behaviour suffers if they don’t get enough. A Python needs up to 18 hours sleep a day, our house-cat companions require just over 12, and yet a giraffe only needs less than 2 hours a night.
Healthy sleeping habits have been linked to immune-system health, better consolidation of memories, healthier appetite, improved energy levels, reduced stress, even reduced risk of heart disease or diabetes (remember folks, correlation is not causation! Some of these factors are still being studied). Even gene expression has been found to be altered by disturbed sleep. Similarly, our sleep can suffer as a result of our daytime lives. Stress, eating habits, hormone levels, bedtime routines, and exercise routines all have their impact.
Even though we need less sleep as we get older (from 16 hours as infants to 7-8 hours as adults), studies have shown that we don’t adapt to sleep deprivation like some other animals. Even if a sleep-depriving schedule becomes habitual, our reaction times, judgement and other faculties remain impaired until we get enough rest. Furthermore, the longer we go not getting enough sleep, the more we get into what is called ‘sleep debt’. The amount of sleep we need to feel better increases the longer we go without sleep.
So make sure you crash, hit the hay, catch some z’s. Nod off, turn in, get more than forty winks if you can. Because it could just be that you bed is your basic best friend when it comes to mental and physical health this exam season.
Aisling Brennan – Science Writer