Posterior slow waves of youth (PSWY) occur amid the alpha rhythm (AR) and are evident because of their longer wave duration. Occurrence when the AR is present does not indicate that PSWY are a form of the AR because they may either disrupt the AR or occur as waves superimposed on the AR (Cervone and Blum, 2007). Similar to the AR, PSWY have a posterior field that is maximal at the occipital poles and they are present only in relaxed wakeful states with the eyes closed. PSWY usually are evident with bipolar montages, but sometimes are better seen with longer interelectrode distances. Channels that include occipital and central electrodes depict PSWY well (Kellaway, 1990).

The PSWY waveform is variable. The wave polarity is inconsistent and the wave duration typically ranges from 0.3 to 0.5 seconds (Niedermeyer, 1999). Most commonly, PSWY appear as sporadic, interspersed slow waves, but they may occur as several individual transients that are separated from each other by 1 to several seconds (Fisch, 1999). Less often, they occur in trains that are usually composed of two or three waves occurring over 1 second. Like individual PSWY, the individual waves within a train may vary in duration and waveform, and this may result in a train appearing as one polyphasic wave (Mizrahi, 1996; Niedermeyer, 1999). Individual PSWY also may appear to be polyphasic if the slow wave follows faster background activity and appears to fuse with it. PSWY usually are symmetric and bisynchronous across the occiput but may occur with minor lateralization, which is typically toward the right (Aird and Gastaut, 1959

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