Humans and many other animals sleep. A lot. But why? This puzzle has confounded scientists for decades. When we sleep, we cannot forage, hunt, or reproduce, all of which were essential to our cavemen ancestors. And yet Mother Nature decided that sleep is an essential and complex part of our biology.
It turns out that sleep has a variety of mechanisms that are essential to health, promote cognitive abilities, and improve memory. Unfortunately, many modern societies are sleep deprived without realizing it because we have gotten used to sleeping less. But that doesn't mean it's any less necessary.
Every night, your brain starts off in NREM sleep and transitions over to REM sleep in the early hours of the morning. NREM stands for non-rapid eye movement. There are 4 phases of NREM sleep, each of which is deeper than the preceding one, and your brain slows down to a fraction of its waking activity. The thalamus blocks all input to your sensory cortex, which is why you might not wake up even with noise around you. During this period of sleep, the memories you have made during the day are selectively transferred to your long-term storage.
REM sleep stands for rapid-eye-movement. As per its name, your eyes move rapidly under your eyelids at this point in the night. Neural activity increases to the degree of wakefulness, and your brain makes connections between memories that you might not have made when you are awake. This produces dreams.
How do you know if someone is truly asleep? This is regulated by the circadian rhythm and various hormones. Your circadian rhythm is your inner biological clock. A connected part of your body, called the suprachiasmatic nucleus, regulates this 24-hour cycle based on the amount of light present and melatonin hormones. This is why melatonin is in some sleep medicines, as it can change your 24-hour cycle.
When it is time to sleep another hormone called adenosine makes you feel sleepy. Because this hormone can only be purged by sleep, it will add up if you don't get enough sleep. That's why when you don't sleep, you feel increased urges to do so. Caffeine works by blocking the receptors for this hormone, but adenosine builds up behind the caffeine, causing a "crash" after its effects wear off.
The circadian rhythm and adenosine cycles aren't as perfectly lined up as you would think. They are slightly off of each other, which is why you may feel drowsy mid-day and early morning.
Sleep improves your memory and creativity through dreams, which also help people process difficult memories that they might have had. Part of the problem with PTSD is that the brain cannot properly file away painful memories, bringing them back night after night. On the other hand, losing sleep can impair memory and cognitive skills, and may cause difficulty with emotional control. In fact, if one does not get enough sleep, they might take "micro-sleeps" throughout the day, which can be fatal if it occurs while driving.
So how do you get good sleep? Studies have shown that blue light (emitted by electronics) and LED light can impair the release of adenosine, making it harder to fall asleep. Keep devices out of the bedroom and try to replace any LED lights. It is also difficult to sleep if even a small amount of light is in the room, which is another reason to replace LED.
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