A comparison of electrophysiological changes during the sleep onset period of psychophysiological insomniacs, psychiatric insomniacs and normal sleepers
The EEG of the sleep onset period of
psychophysiological insomniacs, psychiatric insomniacs and
controls was compared using power spectral analysis (FFT).
Eighteen drug-free subjects were equally divided into three
groups according to their responses in the Brock Sleep and
Insomnia Questionnaire, the Minnesota Multiphasic
Personality Inventory and the Sleep Disorders Questionnaire.
Group 1 consisted of psychophysiological insomniacs, group 2
included insomniacs with an indication of psychiatric
disturbances, and group 3 was a control group. EEG, EOG and
EMG were recorded for two consecutive nights. Power
spectral analysis (FFT) of EEG at C4 from the sleep onset
period (defined as lights out to the first five minutes of
stage 2) was performed on all standard frequency bands,
delta: .5-4 Hz; theta: 4-8 Hz; alpha: 8-12 Hz; sigma: 12-15
Hz beta: 15-25 Hz. Psychophysiological insomniacs had less
alpha during wakefulness than the other two groups and did
not show the dramatic drop in alpha across the sleep onset
period, which characterizes normal sleep. They also had
less delta, especially during stage 2 on night 2. They also
showed less delta in the last quartile of the chronological
analysis of the sleep onset period. Psychiatric insomniacs
showed lower relative beta power values overall while
psychophysiological insomniacs showed higher relative beta
power values during wakefulness. This microanalysis
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confirms that the sleep onset period is generally similar
for psychiatric insomniacs and normal sleepers. This may be
due to the sample of psychiatric insomniacs being
heterogeneous or may reflect a sleep onset system that is
essentially intact. Psychophysiological insomniacs have
higher cortical arousal during the sleep onset period than
do the psychiatric insomniacs and the controls. Clear
differences in the sleep onset period of psychophysiological
insomniacs exist. The dramatic changes in power values in
these two groups are not seen in the psychophysiological
insomniacs, which may make the discrimination between
wakefulness and sleep more difficult
