Analysis of the vigilance stages in the rat by fast Fourier transformation

The characteristics of the power density spectra of the frontal and occipital cortical EEG between 1 and 31 Hz as well as the total power of the neck muscle EMG during an 8-second epoch were used to differentiate 8 vigilance stages in normal rats. The following stages and the time spent within these stages during a 6-hour recording (9.00-15.00) were evaluated: waking with active EMG (about 127 min), waking (7 +/- 3 min), theta-waking (25.5 +/- 9 min), classical sleep I (dozing; 107 +/- 11 min), classical sleep II (41 +/- 6 min), paradoxical sleep (PS; 30 +/- 9 min), transitional phase (PS spindles; 9.5 +/- 4 min) and transitional dozing (13 +/- 3 min). Two additional stages were differentiated in rats suffering from petit mal: paroxysmally occurring spikes and waves and an especially marked transitional phase. The absolute power spectra of these vigilance stages (except active waking) were plotted as well as the statistically analyzed deviations from the mean power spectra of all epochs without active EMG. A comparison between the mean power spectra of a control recording and a recording after oral application of 10 mg/kg diazepam indicates that these differences are less marked than between the vigilance stages.