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.
