Theta waves are seen when one is drowsy. It is difficult to determine twin similarity using squiggly EEG waves like those shown above. To simplify our task, we can use a computer to draw a picture, called a spectrum, that tells us how much of each type of EEG wave is present. These spectra were obtained from twins who were relaxing with their eyes closed. As you can see, what really makes the twins' spectra look the same or different is the amount of EEG alpha that is present.
Some twins produce a great deal of alpha, causing their spectra to have a peak.
Others generate little alpha and therefore have spectra that look relatively flat. In this relaxed state, MZ twins tend to generate the same amount of alpha, producing strikingly similar EEG spectra. DZ twins show far less similarity. If EEG is determined mostly by genes, this is just what we would expect to see. Please be patient.