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Electro-oscillographic recordings show that when rats wake up, behavioral manifestations such as head dorsal extension and snout and eye movements (which occur in this sequence), occasionally followed by brief ear and limb twitches, are preceded by and are simultaneous with theta waves (around 6.5 Hz in frequency) in neocortical areas 3 and 17 and in the hippocampus. Heart rate increases when the animal passes from synchronized sleep to relaxed wakefulness to exploratory behavior. During desynchronized sleep theta waves, similar to those found during alertness, usually precede and are simultaneous with rostrum and eye movements and brief ear and limb twitches. Heart rate also increases during dreaming activity. A high degree of coherence (near 1.0) was found among theta bursts in different hippocampal areas in both highly attentive alertness and dreaming. It is suggested that theta waves are related to attention as part of some kinds of behavior and of the process of dream shaping and expression, both characterized by consciousness.

Establishing the stationarity and statistical distribution of potentials recorded from the nervous system is crucial for the application of frequency analysis. Both parameters were determined in the electrocorticograms of six adult Wistar rats during wakefulness and desynchronized sleep, during both of which desynchronization prevails. Stationarity of the signals was found to occur during at least 20 s in both states of the wakefulness-sleep cycle. A normal distribution was also found for at least 6.7 s. These findings provide strong support for the use of frequency analysis of brain waves as a reliable method to quantify neural electro-oscillograms.

The electrical activity of the posterior thalamic nuclear complex was studied in rats and related to the simultaneous hippocampal electro-oscillogram. Electrocorticographic tracings and spectral analysis showed that during attentive wakefulness the electro-oscillogram peaked at 8 Hz and in desynchronized sleep it oscillated at regular frequencies between 8 and 9 Hz. In quiet wakefulness, frequency was lower (around 6 Hz) and during synchronized sleep rhythmicity disappeared. The electrophysiological patterns during wakefulness and desynchronized sleep are proposed to be linked to the retrieval and combination of information for the generation of attention and dream content.