theta rhythm definition by American Heritage Dictionary
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.
Variant of theta wave
any of the electrical brain waves having a frequency between four and eight hertz and associated with a drowsy, semiconscious state of mind
also theta rhythm