Breastfeeding behaviors can significantly change mothers’ physiological and psychological states. The hormone oxytocin may mediate breastfeeding and mothers’ emotion recognition. This study examined the effects of endogenous oxytocin fluctuation via breastfeeding on emotion recognition in 51 primiparous mothers. Saliva oxytocin was assessed before and after the manipulation (breastfeeding or holding an infant), and emotion recognition tasks were conducted. Among mothers who breastfed daily, mothers with more increased levels of oxytocin after breastfeeding showed greater reduced negative recognition and enhanced positive recognition of adult facial expressions. These oxytocin functions accompanying breastfeeding may support continued nurturing behaviors and also affect the general social cognition of other adults beyond any specific effect on infants.

Unlike mirror self-recognition, recognizing one's own image in delayed video footage may indicate the presence of a concept of self that extends across time and space. While humans typically show this ability around 4 years of age, it is unknown whether this capacity is found in non-human animals. In this study, chimpanzees performed a modified version of the mark test to investigate whether chimpanzees could remove stickers placed on the face and head while watching live and delayed video images. The results showed that three of five chimpanzees consistently removed the mark in delayed-viewing conditions, while they removed the stickers much less frequently in control video conditions which lacked a link to their current state. These findings suggest that chimpanzees, like human children at the age of 4 years and more, can comprehend temporal dissociation in their concept of self.