Do infants exhibit significant cortisol reactivity to the Face-to-Face Still-Face paradigm? A narrative review and meta-analysis

The Face-to-Face Still-Face (FFSF) paradigm is a widely adopted experimental procedure to assess infants' response to socio-emotional stress during the first months of life. Previous reviews demonstrated that this procedure elicits specific behavioral responses, including an increase in negative emotionality and gaze aversion as well as a decrease in positive emotionality and social engagement. Infants also give evidence of hypothalamic-pituitary-adrenal (HPA) axis reactivity to the FFSF. Unfortunately, previous studies reported inconsistencies in the association between the exposure to the FFSF paradigm and HPA activation during the first months of life. In this paper, the HPA axis correlates of FFSF stress regulation were examined through a narrative review and a meta-analysis. A literature search was conducted on three databases (i.e., Scopus, Web of Science, PubMed) and led to 17 studies included in the review and 10 included in the meta-analysis. The findings suggested that infants tend to show a clearly observable activation of the HPA axis in response to the socio-emotional stress elicited by the FFSF paradigm, although considerable variation in methodology and sample characteristics was documented. A five-episode repeated-exposure version of the FFSF procedure emerged as a more suitable procedure to elicit a significant neuroendocrine response. In summary, the FFSF appears to elicit HPA axis activation in response to socio-emotional stress, but only in specific contextual conditions. As such, open questions remain and require continuity in FFSF research efforts.