Neural responses to happy, fearful and angry faces of varying identities in 5- and 7-month-old infants

Abstract

The processing of facial emotion is an important social skill that develops throughout infancy and early childhood. Here we investigate the neural underpinnings of the ability to process facial emotion across changes in facial identity in cross-sectional groups of 5- and 7-month-old infants. We simultaneously measured neural metabolic, behavioral, and autonomic responses to happy, fearful, and angry faces of different female models using functional near-infrared spectroscopy (fNIRS), eye-tracking, and heart rate measures. We observed significant neural activation to these facial emotions in a distributed set of frontal and temporal brain regions, and longer looking to the mouth region of angry faces compared to happy and fearful faces. No differences in looking behavior or neural activations were observed between 5- and 7-month-olds, although several exploratory, age-independent associations between neural activations and looking behavior were noted. Overall, these findings suggest more developmental stability than previously thought in responses to emotional facial expressions of varying identities between 5- and 7-months of age.

Keywords: Emotion; Eye-tracking; Face processing; Infant; fNIRS.

Fig. 1

Paradigm. A. Example stimuli. B. Example trial in the happy condition. The 5 faces shown within a happy block varied in identity, and all displayed a happy expression.

Fig. 2

Top left, diagram of sources (red) and detectors (blue) and their placement relative to the 10-20 system. Top right, front and side photo of probe on 7-month-old infant. Bottom, modeled channel locations and ROI designations displayed on a 7.5-month-old MRI atlas (Richards et al., 2016). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).

Fig. 3

Time-course of grand-mean hemodynamic response averaged over conditions, participants, and ROIs for each age.

Fig. 4

Significant oxyHb activations for each emotional category after correcting for multiple comparisons displayed on a 7.5-month-old MRI atlas (Richards et al., 2016).