<p></p><h2><a name="_Toc29328813">EEG of Sleep</a></h2>

<p>In normal adults, a cycle of sleep
stages repeats throughout the night, about every 90 minutes. This is referred
to as “sleep architecture.”</p><h3>Sleep Architecture over the Course of an Evening of Sleep</h3><p></p><p style="text-align: center; "><img src="@@PLUGINFILE@@/Architecture%20of%20Sleep.png" alt="Architecture of Sleep" width="660" height="383" class="img-responsive atto_image_button_left"><br></p><p></p><p><b>NREM1</b> = Alpha begins to slow
and intermittently drop out of the record and we see a suppression of EEG
amplitude, overall. </p>

<p><b>NREM2</b> = The presence of
Vertex Sharp Waves, K-Complexes, and Sleep Spindles</p>

<p><b>NREM3</b> = The movement towards
complete slow waves (Delta and some low frequency theta)</p>

<p><b>NREM4</b>&nbsp; = Deep dreamless sleep, aka “Slow Wave Sleep
(SWS)</p>

<p><b>REM</b> = Rapid Eye Movement
Sleep</p>

<p>Some schools of thought now combine
Stage 3 and Stage 4 of sleep.</p><p></p><h3><a name="_Toc29328814"><br></a></h3><h3><a name="_Toc29328814">Vertex Sharp Waves</a></h3><img src="@@PLUGINFILE@@/V%20Waves.png" alt="V-Waves" width="402" height="683" class="img-responsive atto_image_button_left">Vertex sharp wave transients, appear in Stage NREM2 sleep. These midline sharp waves run down the vertex and are typically theta in frequency and are of high amplitude. A surround may present at the left and right leads. &nbsp;Vertex sharp waves are usually biphasic. They can occur individually or in runs (repeatedly for a brief time). The morphology of V waves varies in sleeping individuals. In some cases, they are sharply contoured, in other cases they can look like epileptiform discharges.&nbsp;<br><p></p><br><p></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p></p><h3><a name="_Toc29328815"><br></a></h3><h3><a name="_Toc29328815">Stage NREM 2 Sleep and Sleep Spindles</a></h3><p><a name="_Toc29328815"></a></p><h4><a name="_Toc29328815">Sleep Spindles</a></h4><a name="_Toc29328815"><img src="@@PLUGINFILE@@/sleep%20spindles.png" alt="Sleep Spindles" width="492" height="687" class="img-responsive atto_image_button_left"><br></a><p></p>

<p>Sleep spindles,
indicate the onset of Stage NREM2 sleep. They serve as a stabilizing mechanism
during sleep state, which will prevent the individual from awakening. Sleep
spindles are bursts of sinusoidal 12-14 Hz activity, that wax and wane (travel
in an envelope). They are seen over the fronto-central head regions, most often
with a maximum over the central midline. They last from half a second to two
seconds on average.</p><br><p></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p></p><h3><a name="_Toc29328816"><br></a></h3><h3><a name="_Toc29328816"><br></a></h3><h3><a name="_Toc29328816">K Complexes</a> </h3><img src="@@PLUGINFILE@@/K%20Complex.png" alt="K Complex" width="570" height="683" class="img-responsive atto_image_button_left"><p>K complexes usually appear
in Stage NREM&nbsp; of 2 sleep, and may also
seen in Stages N3 sleep.. K-complexes consist of a broad vertex sharp waves
accompanied by a run of sleep spindles.</p>

<p>The slow wave portion of
the K complex can exceed 1000 milliseconds in duration. The amplitude may
exceed 400 microvolts. K complexes appear spontaneously, or they can be
elicited by an auditory stimulus (the “k” in K-complex stands for “Knock”).&nbsp; Knocking a counter, clapping, or tapping a
pencil on a hard surface are good ways to elicit K complexes during EEG
recordings. K complexes should be of equal voltage over both hemispheres.</p><br><p></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p><br></p><p></p><p>Stage N3 sleep is
characterized by an increase in higher voltage slow waves in the theta and
delta range. Sleep spindles and K complexes may be present. As Stage N3 sleep
progresses, the frequencies seen are slower and the number of sleep spindles
decreases.&nbsp; </p>

<p>In NREM 4, delta increases, sleep
spindles are no longer present, and the EEG consists of generalized, high
voltage, irregularly shaped slow waves.&nbsp;
Deeper sleep stages are seldom seen in routine EEG recordings unless the
patient is sleep deprived and the recording period is lengthened.<b></b></p><p></p><h3><a name="_Toc29328818">Rapid Eye Movement (REM) Sleep</a></h3>

<p>REM sleep begins 60-90 minutes
after sleep onset. During REM sleep we lose muscle tone, except for eye
movements. Respiration and heartbeat may become irregular. </p>

<p>During REM sleep, small muscle
movements (phasic twitches), are seen in the face and extremities. Saccadic eye
movements accompany REM sleep, which can be seen under the person's closed
eyelids. The EEG in REM sleep is of low voltage, with a mixture of rhythms. It
may look very much the same as the EEG during wakefulness with eyes open,
except for the lack of EMG contamination.</p>

<p>If REM sleep that begins less than
one hour after sleep onset, it is called REM onset sleep. This can be an
abnormal finding indicating a sleep disorder called narcolepsy if accompanied
by other symptoms and repeatedly demonstrated.</p><br><h3>The Vigilance Model</h3><p>When you are recording an EEG, its advisable to avoid drowsy data, at all costs. Of course, we first have to know what a drowsy EEG looks like. To understand what data begins to look like as someone falls asleep, it is wise to reference the Vigilance Model.&nbsp;</p><p><br></p><h4>What is Vigilance?</h4><div>The
regulation of vigilance and its flexible adaptation to internal and
environmental needs are of fundamental importance for all higher organisms.
Vigilance has to be
adapted to the respective environmental situation, ensuring a high vigilance
level in situations of danger and a reduced vigilance level during times of
recreation.</div><div><br></div><h4><span>Vigilance stages</span></h4>

<div>These states correspond to different levels of alertness at the behavioral
level. Several stages can be separated during the transition from tense to
relaxed wakefulness and further on to drowsiness until sleep onset.</div><p></p><p></p><img src="@@PLUGINFILE@@/Vigilance%20Model.png" alt="Vigilance Model" width="673" height="500" class="img-responsive atto_image_button_left"><br>The VIGALL model of vigilance is meant to be applied to an eyes closed EEG, but it can be even more telling for an eyes open EEG, as you can see when someone descends from the common, eyes closed occipital alpha (A1), to anteriorized alpha (A2) (the first hint that they are getting drowsy and their vigilance is compromised) to a low voltage state (also called desynchronized or alpha drop-out, B1) until you see them descende into NREM2, which corresponds with the C state.&nbsp;<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br>The video just below shows an individual entering stage B1, where we see moments of alpha drop out, where it appears the EEG gets flat.<br>&nbsp;<video controls="true"><source src="@@PLUGINFILE@@/B1.mp4">@@PLUGINFILE@@/B1.mp4</video>&nbsp;<br>And these are the maps and a spectral plot that correspond with the B2 state, high theta and delta power:<br><img src="@@PLUGINFILE@@/Sleep.png" alt="sleep" width="700" height="444" class="img-responsive atto_image_button_left">&nbsp;<img src="@@PLUGINFILE@@/sleep%202.png" alt="sleep 2" width="655" height="560" class="img-responsive atto_image_button_text-bottom"><br>And the video below is someone actively in stage nREM2 of sleep, noted by the vertex sharp waves and beta spindles.<br><video controls="true"><source src="@@PLUGINFILE@@/NREM2.mp4">@@PLUGINFILE@@/NREM2.mp4</video><br>&nbsp;<br><p></p>