Theta Waves
Theta waves are a frequency of electric wavelength that is produced by the brain. It can be measured by an electroencephalograph (EEG) either directly from the brain or through the use of electrodes that are attached to the scalp. One form of theta wave known as the hippocampal theta rhythm is a very strong signal that has been measured in many species of mammals. Cortical theta rhythms are lower frequency and have been recorded only in humans.