Our sleep consists of around 90 minute sleep cycles with four stages each, both at night and during naps. A nap can last anywhere from five minutes to three hours, and it can encompass all stages of sleep or just a few.
Stage 1 is the first two to five minutes of sleep after you fall asleep. The second stage lasts roughly 30 minutes. Body temperature decreases, muscles relax, and respiration and heart rate become more regular in Stage 2. Your neurons begin to fire in sync, causing waves of activity to sweep across the cortex, punctuated by fast bursts of neural activity known as sleep spindles. As you progress to Stage 3, or slow wave sleep, the rolling waves become more prominent as your neurons fire in unison. This phase lasts 20 to 30 minutes and is where your deepest sleep occurs. Then comes REM sleep, which lasts 10 to 20 minutes during a nap. The brain becomes more active in REM, similar to how it is when you are awake. The termination of REM indicates the conclusion of the sleep cycle.
The effectiveness of a nap is determined by a number of factors, including the stages of sleep that are included in the nap. Take a 30 minute siesta that primarily comprises of Stage 2 sleep. Long-term potentiation is linked to stage 2 sleep, a process that is thought to build connections between neurons, which is crucial for learning. A 20 to 30 minute nap falls short of Stage 3’s deep sleep, so it is very easy to wake up from.
Meanwhile, a 30 to 60 minute nap provides the benefits of Stage 2 sleep while simultaneously bringing you into Stage 3 sleep. By linking sleep spindles with slow waves, various brain areas work together to transfer information from short-term memory storage to long-term memory storage, maintaining and strengthening long-term memory. The most difficult stage to awaken from is Stage 3. While a 30 to 60 minute nap can be beneficial to the brain, the effects frequently do not appear until 15 minutes after waking up.
Naps lasting 60 to 90 minutes enter the REM stage. The prefrontal cortex, which is responsible for inhibition and cognitive control, is substantially less active during REM. In the meantime, the amygdala and cingulate cortex, which are involved in emotion and motivation, are quite active. Researchers believe that the combination of these factors causes weird dreams during REM sleep: the loss of inhibition and cognitive control may lead to irrational associations, which, due to the activity of the amygdala and cingulate cortex, might be between emotionally charged issues. Some studies believe that when we wake up, this stage will aid us in making innovative connections between ideas. Even though the nap is longer, but because the brain activity during REM is closer to awakening, it may be simpler to wake up from REM than Stage 3.
It is also important to consider the time of day. Our demand for deep Stage 3 sleep grows stronger as the day progresses. As a result, if you nap later, you may deprive yourself of the sleep pressure required to fall asleep at night. This does not occur during REM sleep. Morning naps are dominated by REM, noon naps have nearly equal amounts of REM and deep sleep, and evening naps have greater deep sleep.
On top of that, we appear to be roughly evenly split between nappers and non-nappers. Non-nappers may not benefit from napping in the same way as nappers do. This could be due to nappers’ ability to stay in a lighter sleep and pass through sleep stages more quickly, according to researchers. Non-nappers, on the other hand, may fall into a deeper sleep while napping, making them tired thereafter.
