5 Amazing Facts About What Happens to Your Body When You Sleep

12% of People Dream in Black and White

Dreams are an important mechanism of the human mind. What seems like a series of random thoughts and events is actually the brain trying to make sense of the day, remembering things that are important, forgetting things that aren’t, and overall preparing our biological computers for tomorrow. While most people dream in full color, around 12% of the population is tuned to TCM (so to speak), and often experiences dreams in only black and white. The analogy to television is an apt one, as researchers discovered in 2008 that people under the age of 25 almost never dreamed in monochrome, while members of the boomer generation and older had dreams devoid of color roughly a quarter of the time. Although it is difficult to prove definitively that TV is to blame, the number of people who reportedly dream in grayscale has slowly fallen over subsequent decades.

Poor Sleep Reduces a Human’s Pain Threshold

Having a poor night’s sleep comes with a multitude of real-world side effects, including sluggishness, irritability, and poor concentration. Over the long term, things get even more dire, as poor sleep can contribute to obesity, high blood pressure, and an overall weaker immune system. Sleep can also have a surprising correlation with how much pain a human can withstand. In 2015, a National Sleep Foundation poll discovered that two out of every three people experiencing chronic pain also suffered from sleep deprivation. Statistics like this inspired scientists from UC Berkeley to figure out how exactly sleep is entwined with pain tolerance. After studying two dozen healthy young adults, the researchers realized the neural mechanisms that evaluate pain signals and activate appropriate relief measures are disrupted when someone doesn’t get enough sleep. Just another reason (among many) that you should always try to get a good night’s rest.

Not Every Person Needs the Same Amount of Sleep

Some people seem to tick along just fine on five hours of sleep while others can’t even think straight on anything less than nine hours. That’s because the common recommendation of getting eight total hours of sleep is really an average — not a rule. Although a common indicator for how much sleep you need is often based on age (for example, kids need more sleep than adults because they’re still growing), differences also occur from person to person. Scientists have identified a significant portion of humans who require less than six hours to feel well rested because these sleep champions actually have a mutated gene that codes certain receptors that affect the sleep-wake cycle. These people experience higher-quality sleep that takes up less time than the average human needs to spend getting shut-eye.

Your Muscles Are Paralyzed During REM Sleep

Dreaming occurs during a process known as REM (rapid eye movement) sleep. The name comes from the physical movement of our eyes while experiencing dreams. During these bouts of REM sleep, of which there are four to six per night, brain activity changes and causes paralysis in our muscles. This normal effect of REM sleep is what’s known as muscle atonia, and it’s designed to keep humans from injuring themselves in their sleep. However, sometimes a person’s muscles still retain function during REM sleep and can cause a person to act out their dreams. This is known as REM sleep behavior disorder, and can be a real danger to the dreamer, or in some cases, the dreamer’s partner.

The reverse is also possible, as sleep paralysis occurs when someone wakes from REM sleep only to discover that they can’t move their body or speak. Both of these sleep disorders (along with many others) are types of parasomnias.

Extreme Sleep Deprivation Can Lead to Psychosis

While being a poor sleeper can have serious side effects, getting no sleep at all can be downright deadly. Throughout the day, our bodies burn energy and create a byproduct in the brain known as adenosine. The buildup of this nucleoside is what causes us to feel sleepy. In fact, caffeine works by blocking adenosine from binding, making us more alert as a result. While we sleep, a waste clearance system known as the “glymphatic system” essentially removes this buildup of adenosine while using cerebrospinal fluid to remove toxic byproducts throughout the central nervous system. After sleeping the required eight (or so) hours, the brain is refreshed and ready for the day ahead. However, if someone puts off going to sleep for a long period of time, adenosine builds up in the brain and eventually disrupts our visual processing system, which in turn triggers hallucinations and, in rare cases, even death. In other words, spending one-third of our lives in bed may seem like a waste of time, but sleeping may be the most important thing we do every day.