Normal Neonatal EEG Background

Normal Neonatal EEG Background

John Giang, MD

Why it matters

A neonatal background is “normal” only when its organization fits the infant’s developmental age and observed state. Features that would be strikingly abnormal later in life—including diffuse slow activity, discontinuity, and asynchrony—may be expected in an immature neonatal recording

Key points

• Start with postmenstrual age and state. One should ask whether expected maturational features are present, whether they match the infant’s clinical age, and whether they are consistent across sleep and wakefulness.
• Background maturation is reflected in increasing continuity, synchrony, and state organization. There is a shortening of maximum interburst intervals with advancing postmenstrual age, alongside development from relative asynchrony toward synchrony.
• Discontinuous background can be normal, particularly at earlier developmental ages (<30 weeks PMA). Interpret bursts and lower-amplitude intervals in context to the neonate’s postmenstrual age, rather than treating discontinuity itself as evidence of encephalopathy.
• The neonatal awake state becomes more continuous, comprising low-amplitude, polymorphic delta to theta activity after 30 weeks PMA. After 35 weeks PMA, the neonatal awake state comprises of medium-amplitude polymorphic delta to theta activity with overriding faster polyfrequencies. 
• Normal maturation includes the timed appearance of recognizable graphoelements, including frontal sharp wave transients (encoche frontales), anterior dysrhythmia, temporal alpha and theta bursts, beta-delta complexes (delta brush), occipital dominant alpha rhythm, vertex transients, and sleep spindles. A few examples are shown in “Benign Neonatal Variants” section.
• Technical setup changes what can be recognized. Neonatal EEGs are commonly reviewed at a compressed paper speed of 15 mm/s, which spreads out the dominant slow activity and facilitates appraisal of continuity, asynchrony, and evolving neonatal rhythms.
• In infants with a head circumference under 36 cm, a reduced neonatal electrode array is often used rather than a full adult-style 10–20 application: close electrode spacing on a small scalp can promote salt bridging. The neonatal montage emphasizes central regions and includes a transverse chain from T3 to T4.

• A small-head neonatal montage with the central emphasis and T3–T4 transverse chain, paired with an example of electrode-bridging artifact.

• Polygraphic channels support correct state assignment: alongside EEG and ECG, neonatal recordings may include EOG, chin EMG, and a respiratory channel.

Common pitfalls

• Calling a preterm pattern abnormal solely because it is discontinuous or asynchronous.
• Calling an awake background in a neonate when they are actually in active sleep (should have less EMG artifact and reactivity than awake).
• Using a dense full 10–20 placement on a very small head and mistaking salt-bridge effects for cerebral findings.
• Reading a neonatal study at an unsuitable display speed and underappreciating slow background organization.

Example tracing set

• Developmentally appropriate discontinuity in a preterm infant

• A more mature neonatal tracing with shorter interburst intervals and greater continuity.