Early maternal mirroring predicts infant motor system activation during facial expression observation

Abstract

Processing facial expressions is an essential component of social interaction, especially for preverbal infants. In human adults and monkeys, this process involves the motor system, with a neural matching mechanism believed to couple self- and other-generated facial gestures. Here, we used electroencephalography to demonstrate recruitment of the human motor system during observation and execution of facial expressions in nine-month-old infants, implicating this system in facial expression processing from a very young age. Notably, examination of early video-recorded mother-infant interactions supported the common, but as yet untested, hypothesis that maternal mirroring of infant facial gestures is central to the development of a neural matching mechanism for these gestures. Specifically, the extent to which mothers mirrored infant facial expressions at two months postpartum predicted infant motor system activity during observation of the same expressions at nine months. This suggests that maternal mirroring strengthens mappings between visual and motor representations of facial gestures, which increases infant neural sensitivity to particularly relevant cues in the early social environment.

Figure 1

Infant mu ERD during execution. ERD during execution of facial expressions in central and occipital clusters in the left and right hemisphere. Error bars represent the mean +/− standard error, *p < 0.05, **p < 0.005.

Figure 2

Infant mu ERD during observation. Mu ERD for each condition (mouth opening, happy, sad, and scrambled) in central and occipital clusters (left and right hemisphere). Error bars represent the mean +/− standard error, *p < 0.05, **p < 0.005.

Figure 3

Infant mu ERD in high and low mirroring groups during observation. Infant mu ERD during observation of mouth opening and happy conditions in the low and high maternal mirroring groups for each expression, in both the left and right hemisphere. Error bars represent the mean +/− standard error, *p < 0.05, ⁺ p = 0.05.

Figure 4

Time-course of stimuli in the four experimental conditions. Each condition included an initial, static/neutral expression, followed by a facial movement which lasted approximately 500 ms. After the movement peak, the expression was held for 1250 ms. Happy and sad stimuli were taken from the Amsterdam Dynamic Facial Expression Set.

Figure 5

Electrode clusters used for analysis of mu ERD. Location of electrodes included in the left/right central clusters (red) and left/right occipital clusters (blue).