Variability of visual evoked responses in the human newborn

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1. 1. Summed visual evoked responses (VERs) were recorded repeatedly during the various phases of the wakefulness-sleep cycle on the first day of life and again 24 h later in six carefully selected full-term human newborns. The obtained VERs were analyzed in terms of wave form changes and amplitudes and latencies of the various wave components. 2. 2. A single subject showed an invariant wave form throughout a recording session. Only the P 2 wave component was always present in all subjects, and it was the only component of relatively invariant latency within subjects. Amplitudes of all components were extremely variable. No relationships could be demonstrated between phases of the wakefulness-sleep cycle or presence of REMs or both on the one hand and (1) presence or absence of any component of the VER, (2) latency of any component of the VER, and (3) peak-to-peak amplitudes. No relationships could be demonstrated among latency and amplitude changes of components of the VER. 3. 3. The following conclusions are reached: (1) The VER of the human newborn is extremely variable. (2) Only the latency of the P 2 component is consistent enough to be used to characterize a subject, but even it does not correlate with its own value a few weeks later. (3) Unless the factors related to its variability can be specified and controlled, the neonatal VER will be of limited value as a tool in clinical measurement or in other individual applications as compared with VERs recorded in older subjects. The principal exceptions would seem to be total absence, extreme distortion and marked and persistent asymmetry of responses. 4. 4. The neonatal VER is, however, very useful for the study of developmental changes in groups and for comparison of groups. 5. 5. It is emphasized that these results do not bear upon the usefulness of the VER beyond the neonatal period.