Vagal modulation of 1-month-old infants to auditory stimuli is associated with self-regulatory behavior

During infancy, cardiac vagal modulation has been associated with attentional and social engagement behaviors. While studies have shown that infants display a behavioral repertoire that enables them to interact with others by being able to regulate themselves in order to attend to and to discriminate emotional and social cues, vagal modulation to sensory stimuli and its association with behavioral outcomes at early ages remains to be addressed. In this study, we analyzed the cardiac vagal response of 1-month-old infants to two auditory stimuli intensities and whether vagal response was associated with social interactive and self-regulatory abilities. Therefore, we recorded cardiac and respiratory physiological responses in 28 infants using a Biopac System. Neurobehavioral assessment was performed using the Neonatal Behavioral Assessment Scale. We observed increased respiratory sinus arrhythmia (RSA) amplitude to both auditory stimuli intensities when compared to baseline. No intensity effect was found for the RSA response. Additionally, we observed that higher RSA amplitude to both auditory stimuli was positively correlated with adjusted self-regulatory behaviors, suggesting a convergence between multiple measures assessing infants' state regulation. Results are discussed in light of 1-month-old infants' auditory stimuli processing and its implications for regulatory behaviors and the emergent social-like behaviors.