Abstract
ABSTRACTThis study investigated modulation of the acoustic cardiac reflex (ACR) in human neonates. Three groups of 16 human neonates born at term were presented an abrupt cardioacceleratory auditory stimulus during awake (AW), quiet sleep (QS), and active sleep (AS) states of wakefulness. On 3/4 of the trials this stimulus was preceded by a continuous pure tone at lead times of either 100, 250, or 4000 ms. Across state, prestimulation modified the amplitude and pattern of the neonatal ACR. Relative to trials without prestimulation, the 100‐ms lead inhibited, whereas the 250‐ms and the 4000‐ms lead stimului enhanced the ACR. During AS, neonates exhibited a triphasic ACR that returned to baseline within 9 s in contrast to the sustained responses in AW and QS states. The results demonstrate central inhibitory and facilatatory control over the ACR early in postnatal life. The pattern of results is consistent with the adult pattern of acoustic startle modulation, as is the absence of significant state effects. Given data from 2‐month‐old infants suggesting an absence of inhibitory effects in acoustic modulation of cardiac startle, it appears that there are non‐linear changes in this basic sensory processing mechanism during the first months after birth.
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