Midline theta rhythm.
Thirty-six patients had a midline theta rhythm in the electroencephalogram that consisted of a train of rhythmic waveforms in the theta frequency range (4 to 7 Hz), which occurred as a focal rhythm in the midline leads and was usually most prominent in the central vertex lead. The activity consisted of sinusoidal or arciform waveforms that waxed and waned. There was variable reactivity of the midline rhythm to eye opening, alerting, and limb movement. Of the 36 patients, 28 had a seizure disorder, while the other eight had various conditions unassociated with epilepsy. The pattern was not associated with epileptiform activity, mu activity, a drowsy pattern, or medication effect. Although its mechanism of origin is uncertain, the midline theta rhythm appears to represent a nonspecific electroencephalographic pattern that can occur in a mixed group of patients with various diagnoses.