The average adult sleeps 7 1/2 hours a night in five 90 minute sleep cycles. Each of these five sleep cycle is composed of five separate levels of sleep: Alpha, theta, delta, rapid eye movement (REM) and then back to theta. The first three sleep levels last 65 minutes. REM lasts 20 minutes and the final level of sleep lasts 5 minutes. The number of hours you sleep is less important than the number of complete sleep cycles you have when you sleep. Five complete sleep cycles a night is optimal.
But why do we sleep? The science on sleep is still a work in progress. But there are a few things they do know for sure:
- Sleep helps form memories – The hippocampus and neocortex send signals back and forth to each other thousands of times during the REM portion of sleep. This process allows memories to stick.
- The REM (Rapid Eye Movement) phase of the sleep cycle is where most of your dreaming occurs. It is also known for the side to side movement of your eyes. Do you know why your eyes move from side to side? That movement oxygenates your eyes. Why is oxygenating the eyes so important? Because the cornea has not blood cells to provide oxygen to the eyes. Without enough Oxygen the cornea warps and becomes less transparent and will develop scars, making it hard to see.
- Sleep makes your brain cells bigger – Sleep increases the size of your myelin sheath. The myelin sheath insulates the axon branches on each brain cell. Without the myelin sheath brain cells would not communicated with each other. The thicker the myelin sheath the faster brain cells communicate with each other. Individuals who have thicker myelin sheaths around their axons are smarter than those who have thinner myelin sheaths.
- Sleep restores willpower – When willpower is depleted we become unable to focus and think clearly, causing us to make bad decisions.
- Sleep allows our conscious mind to communicate with our subconscious mind – Sleep enables offline communication between the conscious mind (aka neocortex), which shuts down during sleep, and the subconscious mind (limbic system and brain stem). This is important because the subconscious mind is regularly taking in sensory data that is invisible to the conscious mind. When we experience intuition, this is actually the conscious mind telling us something the subconscious mind communicated to it during the last sleep cycle.
- Sleep makes learning stick – During REM sleep what we’ve learned the day before is transported to the hippocampus. If we do not complete at least four 90 minute sleep cycles a night, long-term memory storage becomes impaired. Completing at least four sleep cycles the night after learning a new skill or the night after studying for a test locks in the new skill or study material. If we get less than four complete 90 minute sleep cycles the night after learning a new skill or the night after studying for a test, it is as if we did not practice the skill or did not study at all because it never fully gets transferred to long-term memory.
Now you know why we sleep. So, go gets some sleep.