Neurophysiological aspects of neonatal seizures

Recently, amplitude-integrated EEG (aEEG) has been increasingly used and proved useful in neonatal intensive care units (NICU) for the management of neonatal seizures. It does not replace, but is supplementary to standard EEG. This article reviews some of findings obtained with standard EEGs, and tries to interpret them with recent findings in the field of basic science. Seizures mainly occur in active-REM sleep in neonates. This is in sharp contrast to those in older children and adults, in whom epileptic seizures occur mainly in NREM sleep. This may be explained by neurotransmitter effects on sleep mechanisms of the neonatal brain that are different from those of older individuals. When all clinical seizures have no electrical correlates, they are non-epileptic, but when the correlation between clinical seizures and frequent electrical discharges are inconsistent, they should rather be considered epileptic, reflecting progression of status epilepticus causing electro-clinical dissociation. Electro-clinical dissociation is not a characteristic of neonatal seizures per se, but a feature of prolonged status epilepticus in adults as well as children. It occurs when prolonged status epilepticus itself causes a progressively severe encephalopathy, or when status occurs in the presence of a severe underlying encephalopathy. In neonates without pre-existing brain damage, frequent seizures per se may cause mild depression characterized by the loss of high voltage slow patterns, an important constituent of slow wave sleep reflecting cortico-cortical connectivity. Mild depression only in the acute stage is not associated with neurological sequelae, but previously damaged brain may be more vulnerable than normal brain.