What is Sleep Architecture?
You may have heard this term used before, it refers to the different stages that make up our sleep. Understanding these stages of sleep help scientists and clinicians target treatments for insomnia.
Sleep is divided into two stages: Non-rapid eye movement (NREM) and Rapid eye movement (REM). NREM is further divided into four stages, numbered 1-4. Stage 1 is the drift off into drowsiness and it usually lasts about 5 -10 minutes. If you were awakened at this time, you’d probably feel like you never fell asleep.
In stage 2, brain waves slow and eye movements stop. You may observe some muscle twitching in someone in this stage of sleep. Stages 3 and 4 are deep sleep and brain activity will show slow delta waves. Stages 3 and 4 are responsible for the restorative effects of sleep and allowing us to wake feeling refreshed.
NREM sleep cycles throughout the night usually lasting 90-110 minutes for each cycle. This means usually 90 minutes after falling asleep, you enter REM sleep, which is when we dream. When we cycle through NREM, it goes Stage 1, 2, 3, 4, 3, 2, REM. Therefore, we enter into a lighter stage of sleep when we are dreaming. Our brain has heightened activity but our muscle groups are paralyzed. This paralysis is temporary and normal during this stage of sleep as it prevents us from acting out our dreams. Some disorders of sleep inhibit the muscle paralysis and the person can sleep walk or act out their dreams while their brain is still sleeping.
There are several REM periods throughout the night, the first one lasting about 10 minutes and each subsequent one getting longer. It is thought that the last REM period lasts about 1 hour. This means you can have several dreams throughout the night, but since the last one is the longest, it is this dreamtime that you are most likely to remember.