Maturation and topography of the auditory evoked response of the prematurely born infant.

The behavioral, EEG, and auditory responses have been studied during the maturation of prematurely born infants. It was found that: (1) The less mature the infant, the less time spent in a quiet sleep state. As the infants matured, periods of quiet sleep occurred for longer durations and interrupted the active sleep phase more frequently. (2) The EEG pattern of young infants (23–26 weeks estimated conceptional age [ECA]) consisted almost entirely of an “intermittent” pattern. As maturation progressed, this “intermittent” pattern became more closely associated with periods of quiet sleep. The continuous pattern appearing at approximately 29 to 31 weeks (ECA) was increasingly associated with an active sleep phase; by 34 to 35 weeks (ECA), the correspondence between EEG pattern and sleep state was more constant. (3) All infants regardless of conceptional age responded to the auditory stimulus from all recorded areas of the scalp. A sequence of wave patterns of the auditory evoked response was noted as a function of maturation. The young infants had a large, negative, long-latency (180–270 msec) wave diffusely over the scalp. As maturation progressed, a series of negative-positive-negative components was recognized. The evoked response patterns changed wave latency-amplitude relation as a function of both age and scalp topography. (4) The latency of the evoked response waves N1 and P2 were consistently greater during the intermittent, compared to the continuous EEG pattern in infants 34 to 40 weeks age post conception. (5) A small, (early ∼ 15 msec) auditory evoked response was recorded from the ear electrode and is probably of muscle origin. This early muscle response was augmented when the baby was awake and crying, intermediate in amplitude during an active sleep period, and barely detectable or absent during quiet sleep.