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Insomnia as
a symptom is assessed by self report of the quality and amount
of sleep, by definition. Sleep patterns, however, can be physiologically
assessed using somnography, referred to as polysomnography (PSG).
Various PSG sleep variables have been investigated as possible
physical correlates for insomnia. Because there is not always
a perfect, or even close, correlation between perceived and PSG-measured
sleep variables, PSG evaluation is not recommended for the routine
clinical assessment of insomnia (although it may be necessary
to rule out other sleep-related disorders). From a research perspective,
however, PSG sleep assessment is important for revealing variants
of insomnia and expands the realm of measurement for describing
insomnia and responses to treatment.
PSG results
cannot be thought of as surrogate indicators of the symptom of
insomnia, i.e. the presence or absence of PSG sleep changes do
not definitively indicate the presence or absence of insomnia.
The use of PSG assessment, however, broadens the means by which
to probe insomnia within the technological limitations of this
non-invasive measure of brain function.
PSG incorporates
recordings of surface brainwave activity (electroencephalogram,
EEG), facial muscle tension (electromyogram, EMG), and eye movements
(electrooculogram, EOG) on separate recording channels of a polygraph
(called somnograph). The EEG during sleep reflects the summation
of neuronal synaptic events that can be recorded by surface electrodes
placed on the scalp, generally according to standard placements
(Rechtschaffen
and Kales, 1968). Click
here for a diagram of standard electrode placements.
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