Normal Pediatric EEG

Written by Sarah Durica, M.D. and Trent Tollefson, M.D.

Pediatric Awake EEG

Similar to adult EEGs, normal infant and child EEGs have an expected organization. Because the brain develops rapidly in the neonatal period, normal background organization changes weekly for preterm and early term neonates and is not included in this discussion. Beginning at 44 weeks conceptual age, the EEG background should be continuous but will not yet show mature features such as a posterior dominant rhythm or a clear anterior–posterior gradient. The background is largely delta, with increasing theta and eventually alpha activity as the brain matures. Determining the normal degree of age appropriate slowing can be challenging for those less familiar with pediatric EEG. By adolescence, the EEG background is similar to that seen in adults. As in adults, features such as eye blinks and the presence of a posterior dominant rhythm help distinguish wakefulness from sleep.

A 3-4 Hz posterior dominant rhythm (PDR) typically emerges around 3-4 months and increases in frequency with age. A PDR that is slower than expected for age may indicate dysfunction. In childhood and adolescence, this rhythm often rides on underlying delta waves—posterior slow waves of youth—which are normal.

Maturation of the Posterior Dominant Rhythm (PDR) Age Typical PDR Frequency* 3-4 months 3-4 Hz 6 months 4-5 Hz 12 months 5-7 Hz 2 years 6-7 Hz 3 years 7-8 Hz 8 years 8-10 Hz 15+ years 8.5-10 Hz

• Note: mean/average PDR ranges differ by resource and should be interpreted within the context of the entire EEG. In children, the PDR may be admixed with slower frequencies.

Figure 1: Normal awake EEG in a 7-month-old child. Note a 5-6 Hz PDR with a background comprised largely of theta and delta frequencies. Image credit: Lynn Liu.

Figure 2: Normal awake EEG in a 2-year-old child. Note a 7 Hz PDR that becomes more prominent with eye closure. As compared to Figure 1, the background is comprised largely of theta activity with significantly less prominent dela activity. Image credit: Lynn Liu.

Figure 3: Normal awake EEG in an 8-year-old child. Note a 10 Hz PDR that disappears with eye opening. There is continued decrease in waking delta with a shift towards theta and alpha frequencies. Image credit: Lynn Liu.

Figure 4: Normal waking background in a 9‑year‑old child. The posterior dominant rhythm is 8.5 Hz. Intermittent posterior delta waves with superimposed alpha activity are present, consistent with normal posterior slow waves of youth (arrows). Image credit: Lynn Liu.

Pediatric Drowsiness and Sleep EEG

Normal sleep features also evolve with age. Hypnogogic hypersynchrony is normal in drowsiness beginning around 6 months and is characterized by bursts of high-amplitude delta and theta slowing. Hypnopompic hypersynchrony is similar in appearance but occurs during the transition from sleep to wakefulness.

Figure 5: Normal drowsiness with hypnagogic hypersynchrony, high amplitude delta and theta slowing, in a 2-year-old child. Image credit: Chelsea Ortman.

In term infants, frontocentral sleep spindles appear around 6 weeks to 2 months. Due to immature myelination, early sleep spindles are asynchronous, occurring at different times on the left and the right. They are often longer and higher frequency than adult spindles. Although spindles prior to age 2 appear asynchronously, they should be symmetric. Absence of spindles on one side suggests a focal abnormality. Spindles should be synchronous by age 2. Vertex waves and K complexes are present by 6 months in the same regions as adults, though pediatric vertex waves can have a broader spatial distribution, appear in repetitive runs, and look sharp, which may be mistaken for epileptiform activity. By 1 year, all sleep stages should be recognizable.

Figure 6: Normal stage 2 sleep in a 2-month-old term infant. Note the symmetric and asynchronous sleep spindles (brackets). Image credit: Trent Tollefson.

Figure 7: Normal stage 2 sleep in a 2-year-old child. Synchronous and symmetric, high amplitude sleep spindles are seen (brackets). Image credit: Chelsea Ortman.

Figure 8: Normal prominent vertex waves in a 9-year-old patient (brackets).