Sleep 101, Part 2
What’s Really Going on Between the Sheets?
Before the 1950s, scientists believed we just drifted off to sleep and that our brains and bodies went into ‘shutdown’ mode, a passive state that allowed recovery from the previous day. With advancements, researchers have learned that sleep is way more complicated and far more active. In fact, while we are getting our Zzz’s, our bodies are going through various patterns of activity.
The Sleep Cycle A sleep cycle lasts about 90 minutes, through five stages of sleep. The first four stages make up Non-Rapid Eye Movement (NREM) sleep and the fifth stage is when Rapid Eye Movement (REM) sleep occurs.
NREM Sleep Across these four stages, we move from very light sleep during Stage 1 down to very deep sleep, in Stage 4.
Stage 1 Within minutes of nodding off, your brain produces alpha and theta waves and your eye movements slow down. This brief intro to sleep lasts about 5-7 minutes, is quite light, and allows for easy waking. This is the stage where catnaps occur.
Stage 2 During this stage, which is also fairly light and lasts 10-25 minutes, the brain has sudden increases in brain wave frequency, known as sleep spindles, followed by brain wave slowing. If you want to power nap, this is the stage to wake after.
Stages 3 & 4 Stage 3 is the beginning of deep sleep, as the brain begins to produce slower delta waves. There is no eye movement or muscle activity, and it is harder to be woken up. As we move into Stage 4, our brains produce even more delta waves and we move into an even deeper and more restorative sleep. We produce growth hormones for tissue repair, boost immunity, and generate energy for the next day. This stage lasts about 20-40 minutes.
REM Sleep As the name implies, during this final stage of sleep, we have bursts of rapid eye movement. We enter this stage about 90 minutes after initially falling asleep, and each stage can last up to an hour as the night progresses. This is the stage where dreaming occurs. It is thought that our eye movements relate to visual images in our dreams, but this has not been confirmed, nor has the actual reason for the eye movement. This stage is important for learning and memory, as this is when we consolidate and process information from the day, so it can be stored in long-term memory.
What happens over a typical night? It is not as simple as putting four to six of these 90-minute cycles together. Over the course of the night, the amount of time we spend in each stage of sleep begins to shift. During the first 2-3 sleep cycles, we spend more time in deep NREM (Stages 3 and 4), whereas during the final 2-3 cycles, we spend more time in REM sleep. But, we also know that the more restorative NREM sleep tends to occur in the earlier hours of the night (e.g. 11pm-3am) and more REM sleep in the later hours (e.g. 3am-7am), showing us why the general notion that going to bed earlier is better for us.
Join me next month when we explore how we can extend our sleep, improve Stages 3 and 4, and ensure our most restful sleep.