Variations in slow wave activity during sleep in the rat

Scoring of human electroencephalogram (EEG) recordings usually includes subdivisions of non-rapid eye movement (NREM) sleep based on amount of slow wave activity. This procedure has revealed relationships between slow wave activity and many other variables. In animals, however, few experimenters have described variations in slow wave activity within NREM sleep. The present study quantifies, by filtering and integration techniques, variations in amount of slow wave activity during NREM sleep in the rat. Slow wave activity was found to be greatest at the start of the light period; the diurnal variation of slow wave activity within NREM sleep was correlated with variations in amount of NREM sleep. An amplitude criterion was used to define NREM sleep, but overall EEG amplitude during NREM sleep did not show the same diurnal variation as slow wave activity. The results indicate the value of measuring variations in slow wave amplitude during NREM sleep in animals in addition to overall EEG amplitude.