The science of sleep is a modern one – in fact most scientific information on sleep has been gained in the last 25 years. This is a list of 20 very interesting facts about sleep.
Facts 1 – 10
1. The record for the longest period without sleep is 18 days, 21 hours, 40 minutes during a rocking chair marathon. The record holder reported hallucinations, paranoia, blurred vision, slurred speech and memory and concentration lapses
2. Ducks at risk of attack by predators are able to balance the need for sleep and survival, keeping one half of the brain awake while the other slips into sleep mode.
3. It’s impossible to tell if someone is really awake without close medical supervision. People can take cat naps with their eyes open without even being aware of it.
4. Anything less than five minutes to fall asleep at night means you’re sleep deprived. The ideal is between 10 and 15 minutes, meaning you’re still tired enough to sleep deeply, but not so exhausted you feel sleepy by day.
5. Dreams, once thought to occur only during REM (Rapid Eye Movement) sleep, also occur (but to a lesser extent) in non-REM sleep phases. It’s possible there may not be a single moment of our sleep when we are actually dreamless.
6. Humans sleep on average around three hours less than other primates like chimps, rhesus monkeys, squirrel monkeys and baboons, all of whom sleep for 10 hours.
7. Diaries from the pre-electric-light-globe Victorian era show adults slept nine to 10 hours a night with periods of rest changing with the seasons in line with sunrise and sunsets.
8. Most of what we know about sleep we’ve learned in the past 25 years.
9. The extra-hour of sleep received when clocks are put back at the start of daylight in Canada has been found to coincide with a fall in the number of road accidents.
10. Experts say one of the most alluring sleep distractions is the 24-hour accessibility of the internet.
Facts 11 – 20
11. British Ministry of Defence researchers have been able to reset soldiers’ body clocks so they can go without sleep for up to 36 hrs. Tiny optical fibres embedded in special spectacles project a ring of bright white light (with a spectrum identical to a sunrise) around the edge of soldiers’ retinas, fooling them into thinking they have just woken up. The system was first used on US pilots during the bombing of Kosovo.
12. The 1989 Exxon Valdez oil spill off Alaska, the Challenger space shuttle disaster and the Chernobyl nuclear accident have all been attributed to human errors in which sleep-deprivation played a role.
13. The “natural alarm clock” which enables some people to wake up more or less when they want to is caused by a burst of the stress hormone adrenocorticotropin. Researchers say this reflects an unconscious anticipation of the stress of waking up.
14. Tiny luminous rays from a digital alarm clock can be enough to disrupt the sleep cycle even if you do not fully wake. The light turns off a “neural switch” in the brain, causing levels of a key sleep chemical to decline within minutes.
15. REM dreams are characterised by bizarre plots, but non-REM dreams are repetitive and thought-like, with little imagery – obsessively returning to a suspicion you left your mobile phone somewhere, for example.
16. Certain types of eye movements during REM sleep correspond to specific movements in dreams, suggesting at least part of the dreaming process is analagous to watching a film
17. Elephants sleep standing up during non-REM sleep, but lie down for REM sleep.
18. Some scientists believe we dream to fix experiences in long-term memory, that is, we dream about things worth remembering. Others think we dream about things worth forgetting – to eliminate overlapping memories that would otherwise clog up our brains.
19. Dreams may not serve any purpose at all but be merely a meaningless byproduct of two evolutionary adaptations – sleep and consciousness.
20. Scientists have not been able to explain a 1998 study showing a bright light shone on the backs of human knees can reset the brain’s sleep-wake clock.