Theta rhythm is largest in the back region of the brain when a person is resting (i.e., resting or tonic theta) and in the front region (frontal lobes [figure 1]) when the person is actively engaged in mental activity (i.e., active or phasic theta). The normal adult waking EEG record contains relatively little theta rhythm. Investigators have reported that tonic theta increases in several neurological states, such as Alzheimer’s disease; tonic theta also increases when cognitive activity decreases. Tonic theta power in alcoholics has been examined in the Collaborative Study on the Genetics of Alcoholism (COGA). Researchers compared eyes-closed resting theta (3–7 Hz) power in 307 alcohol-dependent study participants and 307 age- and gender-matched control subjects (Rangaswamy et al. 2003). The alcohol-dependent group had higher resting theta power at all scalp locations. In both male and female alcoholics, the increased theta power was most prominent at parietal regions (parietal regions are located at the top of the brain, in the back; see figure 1); in males this prominent theta also extended more forward to the central regions. Correlation of drinking
