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A waveform on an electroencephalogram having a frequency of 4 to 8 hertz, recorded chiefly in the hippocampus of carnivorous mammals when they are alert or aroused. Also called theta wave.
a pattern of brain waves (the′ta waves`) with a frequency of 4 to 7 hertz, occurring during light sleep.
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|Noun||1.||theta rhythm - the normal brainwave in the encephalogram of a person who is awake but relaxed and drowsy; occurs with low frequency and low amplitude|