Auditory processing during sleep in preterm infants: An event related potential study

Auditory processing during sleep was investigated in premature infants by auditory event related potentials (AERPs). Twenty-six premature infants (mean GA 30 week– range 25–35) admitted to a neonatal intensive care unit were studied, prior to discharge, in active and quiet sleep at a mean post-conceptional age of 35 weeks. Infant state was determined by behavioral observation according to standard criteria. An auditory odd-ball paradigm was used with frequently occurring ‘standard’ tones at 1000 Hz and infrequent ‘deviant’ tones at 2000 Hz. Waveforms were recorded at Fz, Cz, Pz, T3 and T4 scalp locations. Measurements were performed in 18 patients because 8 preterm infants were excluded since they had less than the required artifact-free deviant trials in each sleep state. The responses to standard tones were equally recorded in both active and quiet sleep, but auditory responses to deviant tones consisting of an increased frontal negativity in the time period from 200 to 300 ms after the stimulus were recorded only in active sleep. A significant effect of electrode placement, for frontal location by sleep condition and sleep condition by 50 ms time windows was shown by repeated measures analyses of variance. The significance of these findings on evoked potential methodology in preterm infants admitted to neonatal intensive care unit is discussed.