How long should your naps be? - Sara C. Mednick
Your eyes get heavy and gradually...
close...
But wait!
It’s only lunchtime
and you still have so much to do.
Would taking a nap help?
Or would it derail your day?
Our sleep, both at night and in naps,
is made up of approximately 90 minute
sleep cycles with four stages each.
A nap can last anywhere from five minutes
to three hours,
so it can include full sleep cycles
or just a few stages.
As you fall asleep, you enter Stage 1:
the first two to five minutes of sleep.
Stage 2 comes next, for about 30 minutes.
In Stage 2, body temperature drops,
muscles relax,
and breathing and heart rate
become more regular.
Your neurons start to fire in unison,
creating waves of activity
that sweep across the cortex,
punctuated by rapid bursts
of neural activity called sleep spindles.
As you enter Stage 3,
or slow wave sleep,
the rolling waves increase as your neurons
fire in coordination.
This phase lasts about 20 to 30 minutes
and is where your deepest sleep occurs.
Then, you enter REM sleep, which lasts
about 10 to 20 minutes in a nap.
In REM, the brain becomes more active,
more like your brain activity while awake.
The end of REM signals
the completion of a sleep cycle.
OK, but will a nap make you feel better?
Well, that depends on a few things—
especially what stages of sleep
the nap includes.
Take a 30 minute nap,
which consists mainly of Stage 2 sleep.
Stage 2 sleep is associated
with long-term potentiation,
a process that's thought to strengthen
the synapses between neurons,
which is essential for learning.
A 20 to 30 minute nap stops short
of Stage 3′s deep sleep,
making it relatively easy to wake up from.
A 30 to 60 minute nap, meanwhile,
has the benefits of Stage 2 sleep
and also takes you into the deeper sleep
of Stage 3.
During Stage 3, multiple brain areas
work together to transfer information
from short-term memory storage
to long-term storage,
stabilizing and strengthening
long-term memory
by coupling sleep spindles
with slow waves.
Stage 3 is the most difficult stage
to wake up from.
So while a 30 to 60 minute nap
can have cognitive benefits,
those benefits often don’t kick in until
about 15 minutes after waking up.
60 to 90 minute naps enter the REM stage.
While in REM, the prefrontal cortex,
which is largely responsible
for inhibition and cognitive control,
becomes much less active.
Meanwhile, the amygdala
and cingulate cortex,
regions associated with emotion
and motivation, are highly active.
Researchers have posited that
the combination of these things
leads to bizarre dreams during REM sleep:
the decrease in inhibition and cognitive
control might lead to wild associations—
and, thanks to the amygdala
and cingulate cortex activity,
those associations can be
between emotionally charged topics.
Some researchers think this stage might
help us make innovative connections
between ideas upon waking.
Because the brain activity during
REM is closer to waking,
it may be easier to wake up from REM
than Stage 3,
even though the nap is longer.
The time of day also matters.
Our need for deep Stage 3 sleep
progressively increases
throughout the day.
So if you nap later,
you may rob yourself of the sleep pressure
needed to go to sleep at night.
This doesn't happen for REM sleep.
Longer periods of REM occur
during morning hours,
so morning naps are dominated by REM,
midday naps have about equal parts
of REM and deep sleep,
and evening naps contain more deep sleep.
On top of all this, it seems
that we’re just about evenly split
between nappers and non-nappers.
Nappers consistently show
cognitive benefits from napping,
but non-nappers may not.
Researchers think this could be
because nappers
are able to stay in a lighter sleep
and move through sleep stages more easily.
Meanwhile, non-nappers may experience
more deep sleep while napping,
making them groggy afterward.
So will a nap help?
Well, there’s only one way to find out...
