Posterior Slow Waves of Youth

Posterior slow waves of youth are a normal finding of high amplitude, theta to delta waves within the PDR that can be bilateral or unilateral, and which usually arise from 3-6 years old and go away by adulthood.

There should be little to no delta activity in wakefulness. However, “posterior slow waves of youth,” in which isolated or occasionally sequential delta waves occur in the posterior derivations during wakefulness, are often with superimposed alpha PDR activity

In children delta activity is common especially in the posterior head region. These physiological slow waves usually occur singly and randomly with intermixed alpha rhythm. The waveform resembles the “sail” of a sail boat, this has sometimes been referred to as a “sail wave.” PSWY are more abundant in younger children. The “posterior slow wave of youth” becomes progressively less prevalent toward the age of 20 years but could be seen as late as 25 years of age. The posterior slow waves of youth are uncommon in children less than 2 years old and become maximum between ages 9 and 14. They are not always symmetric or synchronous between the left and right occipital electrodes and tend to be greater in amplitude and incidence on the right side. They may be more prominent during the early portion of the recording and tend to diminish toward the end of recording.

However, due to the great variation in amplitude, waveform, and occurrence among normal children, it is difficult to distinguish between normal and abnormal posterior delta in an individual EEG. If occipital slow waves occur with the following appearance, they may be considered abnormal:

(a) disproportionately high amplitude as compared to the alpha rhythm (>1.5 times the voltage of the alpha rhythm or >200μV);

(b) serial rhythmic waveform, which constitutes OIRDA (occipital intermittent rhythmic delta activity or occipitally predominant RDA*;

(c) widespread distribution involving the central or midtemporal electrodes;

(d) predominantly unilateral; or (e) persistent after eye opening.

These “posterior slow waves of youth” should not be considered pathologic delta activity unless they are unilateral or disrupt the alpha background.

With increasing age, the alpha rhythm becomes more persistent, but there is underlying delta activity with a superimposed alpha or theta rhythm or intermittent delta activity interrupting the alpha rhythm (posterior slow waves of youth) (see Figs. 7-5 to 7-7 and 7-25). The amplitude may reach 100 to 150 μV (measured at the occipital electrode with an ipsilateral ear reference). During the eyes-open state, the background activity is slower, consisting of an irregular delta–theta pattern (see Fig. 7-11). It is important to assess the background activity while the subject’s eyes are closed, but during the fully awake state. If the subject is too young or mentally challenged and unable to follow the technologist’s commands, eyes closed for 20 to 30 seconds must be recorded by the technologist holding the eyes closed. When the alpha rhythm reaches 10 Hz at about 15 years of age, underlying delta activity and posterior slow waves of youth diminish, and the amplitude becomes close to the adult range (40 to 60 μV) (see Figs. 7-7 and 7-8). In children and adolescents, frontocentral activity may be dominated by theta rhythm despite well-defined and dominant alpha rhythm posteriorly (see Fig. 7-23).