I have been reading my psychology textbook for my Intro to Psych class this week, and I was captivated by the section on sleep. I’ll summarize the most interesting parts here.

When you sleep, you move through five distinct stages, in roughly 90 minute cycles. First dropping off, even though you don’t notice it, there is a distint moment in which you fall asleep – by watching a readout of brain waves there is a sudden shift from alpha waves  -  the brainwaves associated with a relaxed, awake state – to the quieter and more erratic Stage1 waves.

During this phase (which seems to be what we might call “half-asleep”) you may have hallucinations, or feel sensations that don’t exist – you may feel like you are falling, making your body jerk. These sensations are called hypnagogic sensations. Fun word.

At about 20 minutes, you move into a slightly deeper sleep, Satge2. You could be woken easily, but you are definitely asleep. At any point from here sleep-talking may occur.

Then, in the ensuing minutes, you enter stage3 and then stage4,  at which point the delta waves – large, slow brainwaves – start to emerge. You are now deep asleep. It is at the end of this phase that most sleepwalking happens in children.

Finally, an hour after you fall asleep, a very odd thing occurs. You move back through the previous two stages of sleep and you enter REM Sleep – characterized by Rapid Eye Movement. Lasting about ten minutes, your brain activity increases – and your heart rate rises, your breathing gets quicker, and so on.

During this phase, every 30 seconds or so, your eyes dart around quickly (this gives the sleep stage its name).

This is when you dream – and though according to a study 37% of people claim they never have dreams they can remember in the morning, 80% will say they were just dreaming if woken during REM.

You then move through the cycles, and as morning gets closer spend more and more time in REM and Stage2.

Some intersted factoids:

Though the part of your brain that sends signals to move your muscles is active during REM, your brainstem blocks those signals. This means you are basically paralyzed, as no motor signals can get down to your muscles.

• People usually don’t snore during REM.
• Horses have to lie down to experience REM sleep. (they can sleep standing and do often)

• The “hypnagogic” sensations experienced when you are falling asleep also occur when you are waking up – specifically, if you go back to sleep in the morning and hang out in the half-awake phase
• Some people really do need more – or less sleep. Adult’s need for sleep varies between less than 6 and 9 hours. (I’m a 9 person, no doubt about it)
• The early morning light, picked up by your eyes, causes your eyes to send signals to a special part of your brain that adjusts your sleep cycle to the changing dawn and sunset times through the year
• The week after moving the clocks forward in the spring for Daylight Savings – and everyone losing an hour of sleep – accidents increase.
• Your brain cements memory and knowledge at night while you sleep.
• People who reported getting too little sleep generally reported lower satisfaction with their personal life than those who regularly get enough
• Your brain *does* have a sleep memory: your sleep debt racks up for two weeks before your body “forgets” it.
• If you are severly jet-lagged, spending the first day in your new location outside in the sunlight will help your body readjust quickly.

I was riveted. I hope you find it interesting too!