High-frequency components of the rat electrocorticogram are modulated by the vigilance states.

In view of the reports that in the human magnetoencephalogram, 40-Hz oscillations are more abundant in waking and REM sleep than in non-REM sleep, we performed a 24-h broad-band (0.25-64 Hz) spectral analysis of the electrocorticogram in unrestrained rats. Spectral power above 33 Hz was higher in waking and REM sleep than in non-REM sleep, and in the range of 6-38 Hz it was higher in REM sleep than in waking. Consistent frequency-specific changes in spectral power marked the transitions between vigilance states. The study demonstrates that the rat EEG exhibits state- and frequency-specific changes over a large frequency range.