EEG power spectra in sleep-onset insomnia.

EEG power spectra of 12 primary, drug-free, sleep-onset insomniacs and 12 age-matched normal sleepers were compared. Subjects slept for 3 consecutive nights in the laboratory, during which EEGs from C3A2 and O1A2 were continuously recorded on FM tape, in addition to standard EOG and EMG leads. The first unambiguous minute of record from each sleep stage, including wakefulness prior to sleep, was selected from the first sleep cycle of night 3. Analog EEG data from 0.5 to 30.5 Hz were digitized at 128 samples/sec, cosine tapered, and subjected to FFT with a resolution of 1 Hz. Sleep latencies of insomniacs (52.0 min) and normals (12.6 min) differed (P less than 0.001). There were no other sleep stage differences. Non-parametric statistics showed that, during wakefulness, insomniacs had significantly more beta activity and less alpha activity than normals. During stage 1, insomniacs had significantly more beta activity than normals. There were no differences during stages 2, 3, or 4. During REM sleep the insomniacs again had significantly more beta activity than the normals. Data from both EEG leads were generally consistent. Thus, insomniacs have increased beta and decreased alpha activity relative to normals prior to the onset of stage 2 sleep. This agrees with our previous finding of increased presleep physiological activity in insomniacs. However, the present data also suggest that a CNS component of this activity, reflected by increased beta EEG, is reactivated during REM sleep.