Neurophysiological assessment of brain function and maturation: I. A measure of brain adaptation in high risk infants.

Neurophysiologic assessments using EEG/polysomnographic studies permit the clinician to recognize expected patterns of brain maturation in the healthy neonate. By comparison, one can detect encephalopathic behaviors of newborns who are medically at risk. Severe physiologic expressions of encephalopathy are associated with neuropathologic lesions on postmortem examinations, brain lesions documented on neuroimaging studies, and major neurodevelopmental sequelae of survivors. However, such patterns are observed for only a minority of high risk neonates; less severe encephalopathies occur more frequently in neonates without evidence of brain lesions on imaging studies who either recover from medical illness or who manifest no findings of neurological dysfunction. These subtle and persistent brain disorders are obviously more difficult to detect and grade. This is specifically relevant for preterm infants in whom various degrees of encephalopathy may exist, but whose physiologic behaviors must be distinguished form expected behavioral and neurophysiologic patterns of prematurity. Neonates may express brain dysfunction as altered rates of brain maturation, as compared with expected patterns for a given conceptional age. Neurophysiologic expressions of brain dysmaturity, either from prenatal and/or postnatal stresses, may actually occur in a substantially larger segment of the high risk neonatal population than has been anticipated. EEG-sleep studies can serve as a noninvasive neurophysiologic probe of brain organization and maturation to extend clinical observations to assess the severity and persistence of brain dysfunction in a neonate who may be at risk for later neurodevelopmental compromise.