Bilateral hemodynamic responses to auditory stimulation in newborn infants

We studied hemodynamic auditory evoked responses of 20 healthy full-term neonates with near-infrared spectroscopy. The instrument used allows the measurements to be performed simultaneously above both auditory cortices. The stimulation consisted of 5-s trains of sound (700-ms interstimulus interval) with a 25-s silent interval. In response to the stimulation, a significant increase in concentration of oxygenated hemoglobin was detected in 14 out of 21 measurements. The mean latency of the largest response was 9.63+/-2.20 s (mean+/-SD) and the mean amplitude was 1.02+/-0.53 microM. The response amplitude was significantly larger in active (1.28+/-0.59 microM) than in quiet sleep (0.76+/-0.32 microM). The latency of the oxygenated hemoglobin concentration response was significantly shorter (r=-0.70 and p=0.0023) for infants with higher gestational age.