Vagal Tone as a Biomarker of Long-Term Memory for a Stressful Social Event at

ABSTRACT: This study investigates infants’ memory for social stress after a15-day retention interval using behavior and respiratory sinus arrhythmia (RSA).Experimental group infants were exposed to face-to-face still-face paradigm(FFSF) two times; the first time at 4 months and after a 2-week interval.Control group infants were exposed to FFSF only once at 4 months plus 2 weeks.Infants were categorized as suppressors or non-suppressors based on thedirection of RSA change at first FFSF exposure. No behavioral differences werefound among groups and exposure conditions. In the experimental groupsuppressors changed and showed no suppression when re-exposed 2 weeks laterto FFSF. Non-suppressors showed no change in RSA from the first to the secondexposure to FFSF. Control infants showed similar RSA changes to experimentalinfants at their first exposure. Findings indicate that 4-month-old infants havememory for social stress related to individual differences in autonomic reactivity. 2014 Wiley Periodicals, Inc. Dev PsychobiolKeywords: vagal tone; infants; memory; physiological reactivity; social stress;still-face paradigm