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Scenario:
You are planning a descriptive study of insomnia and intend
to monitor its associated physical sleep structure, i.e. you intend
to use both self-report and PSG data. Generally, 30-second segments
(epochs) of the PSG recordings are analyzed for unique or dominant
waveforms and scored accordingly for stage type. The waking EEG
is characterized by very mixed frequency, low amplitude brainwaves.
You know that
non-rapid eye movement (non-REM) sleep progresses from light to
deep sleep as characterized over time by production of increasingly
slower and higher amplitude, more synchronized brainwaves. Non-REM
sleep begins with transitional sleep (stage 1) that is characterized
by low voltage, mixed frequency EEG with a prominence of brainwave
activity in the 2-7 Hz (cycles per second) range. Light sleep
(Stage 2) is characterized by the appearance of intermittent high
voltage waveforms called K complexes. They have a well-delineated
negative (upward) component that is followed by a positive component
(downward) that usually lasts <5 sec on a background of low voltage,
mixed frequency waves. Stage 2 light sleep also has the appearance
of sleep spindles (waveform bursts with a mean frequency of 11.5
to 16 Hz for a duration of 0.5 seconds or more).
The basic
feature of non-REM deep sleep (Stages 3 & 4) is the progressing
amount of high amplitude, low frequency (slow) delta waves in
the 0.5 to 2.0 Hz range, which is referred to as slow wave sleep
(SWS), or called deep or delta sleep. Stages 3 and 4 of deep sleep
are distinguished only by differing proportions of the sleep 30
sec. epoch that are occupied by slow waves > 75µV in amplitude
(stage 3 = 20-50% and stage 4 = >50% of the epoch). In REM sleep
(Stage 5), there is a desynchronization of the brainwaves showing
as faster, mixed frequency waves with lower amplitude, sawtooth-looking
EEG waves, while eye movements are seen on the occulograph channels.
Click
here for a table summarizing these features.
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