New research shows that the amount of time in which breastfed meals are the only source of sustenance has an effect on emotion perception in infants.

The study, published in Frontiers in Behavioral Neuroscience, found that prolonged exclusive breastfeeding — when the infant only receives breast milk without any additional food or drink — was linked to an increased sensitivity to positive emotional information in 8-month-old infants.

“Our results demonstrate that infants who had been exclusively breastfed longer showed an increased neural sensitivity to positive (happy) body expressions,” Kathleen Marie Krol and her colleagues wrote in the study. Infants who had been exclusively breastfed for a shorter period of time “showed an increased neural sensitivity to negative (fearful) body expressions.”

“The finding that such biases in emotional information processing occur in the context of the psychological and biological processes associated with breastfeeding during infancy is testament for a need to better understand the impact that maternal care in general and breastfeeding in particular has on socio-emotional functioning in infancy,” Krol and her colleagues said.

The researchers presented images of body expressions portraying six fearful and six happy expressions to 28 infants, while an EEG recorded the electrical activity in the children’s brains. On average, the infants in the study were exclusively breastfed for about 5 months.

The researchers found that the duration of exclusive breastfeeding was linked to differences in the neural processing of emotional body expressions, even after accounting for variables such as infant temperament, maternal dispositional, interpersonal reactivity, current breastfeeding exposure, and maternal education.

The infants exclusively breastfed less than 5 months showed greater brain responses to fearful expressions than to happy expressions. Infants exclusively breastfed for more than 5 months, on the other hand, showed greater brain responses to happy expressions than to than fearful expressions.

“This is the first evidence to suggest that emotion processing in infancy critically differs as a function of breastfeeding experience, supporting the notion that breastfeeding behavior is a complex biological and psychological process linked to early socio-emotional development,” Krol and her colleagues wrote.

