*6.3.1 Interictal background*

Background activity is normal at the onset of the disease. A characteristic 4–7-Hz diffuse theta rhythm, usually predominating over the central-parietal areas (central theta waves), is often present, intermixed with normal waking activities and increasing during the drowsiness. In some children, background may be diffusely slow. During sleeping, physiological features are usually seen at the onset, while diffuse slowing with loss of sleep architecture can occur during the evolution, mainly in the severe forms of the spectrum [11].
