'Love hormone' oxytocin may help women respond to crying babies
Oxytocin, which is released during labor and nursing, can help turn on the maternal instinct and motivate women to soothe a crying baby, according to a new study conducted by researchers from Indiana University.
The goal of the study was to describe the roles of the so-called "love hormone" and parity on reward area activation in response to reproductive stimuli. The researchers focused on the ventral tegmental area (VTA) and nucleus accumbens (NAc) since those areas are associated with reward.
The researchers predicted that postpartum women would show higher reward area activation to infant stimuli, that women who had not given birth would show higher activation to sexual stimuli, and that oxytocin would increase activation to infant stimuli in women who had not given birth.
The study included 29 women who were six months postpartum and 30 women who had never had children. The women viewed images of crying and smiling infants, sexual activity, and neutral items such as nature photo, and the researchers measured VTA and NAc activation using functional magnetic resonance imaging (fMRI), which measures brain activity by detecting the change in blood oxygenation and flow. Both groups completed the Sexual Inhibition (SIS) and Sexual Excitation (SES) Scales and the Brief Index of Sexual Function for Women (BISF-W) and received either a nasal oxytocin dose or a nasal placebo before viewing the images.
In both groups, the nasal oxytocin increased VTA activation to crying infants and sexual images, but not smiling infants. Women who were postpartum had lower SES, higher SIS, and lower sexual desire compared to women who did not have children.
"We know there are tradeoffs in terms of sexual responsiveness and in terms of attention to a new infant, who requires care and affection," said senior author Julia Heiman, a professor in the Department of Psychological and Brain Sciences. Heiman is also a senior research fellow the university’s Kinsey Institute.
"What changes during the postpartum period, how these changes positively impact the mother and the infant, and to what extent this nurturing response overrides sexuality, we are learning, depends on a number of influences."
Heiman also said that the reason the oxytocin may not have increased VTA activation for the images of smiling infants is because most adults have similar reactions to a smiling infant so fewer differences in "reward" can be found.
The study was published in the journal Hormones and Behavior.