Differential associations between infant affective and cortisol responses during the still face paradigm among infants born very low birth weight versus full-term.

Psychological stress responses may have both emotional and cortisol reactivity correlates, but there are limited data addressing the association between generalized negative and positive emotional states and cortisol reactivity to a psychological stressor among infants born very low birth weight (VLBW; <1250 g) compared to infants born full-term. Examining this relationship between behavioral (affect) and physiological (cortisol) responses may provide insight into the nature of regulation difficulties identified in infants born VLBW. The purpose of this study was to assess the association between infant affective and cortisol responses to the Still Face paradigm (SF) in a cohort of six- to eight-month old infants born VLBW compared with infants born full-term (N=53 total; N=29 and N=24, respectively). Infant affect was coded in 1-s intervals while mother-infant dyads participated in the SF paradigm, and percent positive affect and percent negative affect were calculated separately for each SF episode. We had hypothesized that because infants born VLBW are at increased risk for dysregulation, they would show, compared to full-term controls, greater dysregulation in the form of less synchrony (i.e., less correlated affective and cortisol responses) across the two SF stressors (episodes 2 and 4). This hypothesis was largely supported: the associations between affective and cortisol responses were different for the two groups across the two stressors for percent positive affect (both stressor episodes 2 and 4) and percent negative affect (episode 4 only). For the full-term group, follow up correlations revealed significant negative associations between percent positive affective and cortisol responses for both stressors. Mothers' responsiveness did not explain the term group association differences between infant affective and cortisol responses across stressors. The (lack of) association of stress reactivity systems may index dysregulation or dysregulation correlates in preterm children. Understanding how this lack of coordination among stress systems relates to greater dysregulation, learning, and attentional difficulties may be important in recognizing early precursors to such problems in preterm children, and in this way, aid in early intervention efforts. Future research is warranted to determine how these findings relate to infants' stress reactions in naturalistic settings, and the directionality and temporal relationship between cortisol and infant affective stress responses.