A longitudinal analysis of the development of infant facial expressions in response to acute pain: immediate and regulatory expressions.

Facial expressions during infancy are important to examine, as infants do not have the language skills to describe their experiences. This is particularly vital in the context of pain, where infants depend solely on their caregivers for relief. The objective of the current study was to investigate the development of negative infant facial expressions in response to immunization pain over the first year of life. Infant facial expressions were examined longitudinally using a subsample of 100 infants that were each videotaped during their 2-, 4-, 6-, and 12-month routine immunization appointments. Infant facial expressions were coded using BabyFACS (facial action coding system) for the first minute after a painful needle prick. Facial expressions were examined with a catalogue of the most commonly occurring facial expressions. Results demonstrated that clear differences were seen over ages. Infants display a variety of facial expressions with some of the components of adult pain expressions immediately after the needle and they abate shortly after. However, infants did not display adult expressions of discrete negative emotions. Instead, infants displayed a variety of generalized pain and distress faces aimed at gaining caregiver aid. The development of nonverbal communication in infants, particularly facial expressions, remains an important area of inquiry. Further study into accurately measuring infant negative emotions, pain, and distress is warranted.