00:00
When we think about sleep, there are a number of stages and
we can understand those by their description
what's happening for the patient and changes in the brain.
And we evaluate those
with EEG or electroencephalography. So let's walk through
some of those stages
of sleep. The first is the awake stage and we can be awake
with our eyes open or
awake with our eyes closed. When we're awake with eyes open,
the person is alert
and active and there are prominent beta waves; low
amplitude, very high frequency
waves because the brain is thinking in their stimuli and
things going on. When we
close our eyes, there is a reduction in the stimuli that are
entering our brain through
the eyes. We see a decreased level of alertness in our
relaxation of the brain and
accordingly we see the development of alpha waves on the
brain as that basal
rhythm comes out and there is a reduction in all of that
high frequency thinking
that occurs when the eyes are awake and open. As we move
into sleep, the first
part of sleep early in the night is non-REM sleep and the
first stage is stage 1.
01:09
This is characterized by a transition from wakefulness to
sleep. Patients become
somnolent or drowsy during that early phase and this is the
lightest sleep.
01:21
Typically the EEG pattern during that stage 1 of sleep are
theta waves. As the brain
moves from the alpha calm of wakefulness to the deep sleep
of delta wave sleep.
01:33
Stage 2 sleep is characterized by patients becoming less
responsive and the brain is
going deeper and deeper into sleep. The heart rate goes
down, temperature begins
to decrease, and the body prepares for deep sleep as well as
REM sleep. This is the
longest stage in terms of the total duration of sleep
calculated over the course of
the night. And on EEG, we see theta waves. Sleep spindles
which are bursts of
high frequency, low amplitude activity and K complexes which
are large
discharges of waves. The sleep spindles help to put the
brain to sleep and those K
complexes help to maintain arousal in case the body needs to
wake up for any
reason. And then the brain moves into a slow wave or deep
sleep. And this is
characterized by stage 3 sleep. In this stage, restfulness
occurs. This is the deepest
part of sleep. It is much more difficult to arouse
individuals from this deep stage 3
sleep. Body tissue growth occurs. This is where the brain
and body will repair and
this decreases in duration over the course of life with age.
Here, we see on the EEG
delta waves. These are the highest amplitude, lowest
frequency waves as the brain
is very calm and relaxed and in deep sleep. Next, we see REM
sleep and the
majority of REM sleep occurs very late at night after the
onset of deeper slow
wave sleep. REM sleep is our dream sleep and this is where
the body and brain
will dream. The EEG shows mixed low voltage pattern. In
fact, it looks very much
like an awake brain on the EEG. If we look at electroocular
recordings, we see
rapid eye movements and that's what's characteristic of this
phase of sleep. The
eyes are moving and we can see that both on the electrodes
as well as just looking
at a patient's eyes. We see irregular sharply peaked eye
movements during this phase.
03:40
And very importantly if we record muscle activity through an
EMG. We see atonia
of voluntary muscles. We don't need to be acting out our
dreams and so during REM
sleep the body and muscles have no tone and there is no
movement, inactivity due
to inhibited alpha motor neurons. In certain disorders like
REM behavior disorder,
the brain lose and body loses this atonia with the ability
to act out dreams, and
that's REM behavior disorder. On the EEG, it looks very much
like someone who
is awake. There are beta waves, those high frequency, low
amplitude waves that
occur during REM sleep. So let's look at some of those EEG
patterns. In normal
wakefulness, we see alpha and beta waves. You can see
they're very low amplitude
and high frequency as the brain is thinking and processing
stimuli and many things
are happening in the brain. In stage 1 sleep as the brain
prepares for sleep, we see
theta waves, slightly higher amplitude, slightly lower
frequency as the brain moves
in to a slower wave of sleep. In stage 2, there is this
competition between sleep
promoting signs and wakefulness promoting activity. The
sleep spindles are these
really high frequency low amplitude spindles that put the
brain to sleep and the K
complexes are arousal complexes all occurring on top of
those theta waves. And
findings on the EEG that appear as you see here are
indicative of stage 2 sleep.
05:18
Slow wave sleep that you can see here is very high
amplitude, low frequency
waves that give this stage of sleep its name of slow wave
sleep and here we're
looking at delta waves. And then as we move into REM sleep,
we see the brain
really looks awake. We see the return of beta waves, low
amplitude, high activity
as the brain is processing all the things that are happening
during those dream
states. Now let's talk about some of the environmental
factors that are associated
with sleep and impairments in sleep. Alcohol can
significantly change sleep and
reduce the amount of REM sleep that the body will experience
over the course of
night. Caffeinated drinks change our ability to get to sleep
and maintain a high
quality of sleep. Large meals before bedtime change the
ability of the brain and
body to get in to that REM sleep and the duration of slow
wave sleep. Exercise can
impact sleep. Napping during the day can impact sleep. Light
exposure around
bedtime also changes activity that suprachiasmatic nucleus
and can alter the ability
to get to sleep.