The brains of homosexual fathers adapt to take on the roles of both motherhood and fatherhood, new research has revealed.
While it has been established that having a baby alters the brains of new mothers, this is the first evidence of changes taking place in the brains of gay men who become parents.
A team of researchers led by Ruth Feldman, a neuropsychologist at Bar-Ilan University, filmed 89 new mothers and fathers interacting with their children at home.
They then measured the parents' brain activity while watching the videos in an MRI tube, as well as other videos which did not feature their children.
The 48 homosexual fathers in the study showed an increase in emotional sensitivity and cognitive focus. Their pattern of brain activity was found to reflect those of both new mothers and new fathers, as their emotional circuits were as active as those of the mothers and the interpretive circuits showed the same extra activity as those of heterosexual fathers.
In the 20 mothers in the study, watching their children triggered heightened activity in the brain's emotion-processing regions, such as the amygdala, which was five times more active than when they watched videos that did not feature their children.
It was not established whether this is the result of hormonal and other changes that occur during pregnancy, or whether the pattern is a response to the experience of motherhood.
For the 21 heterosexual fathers, watching their children increased the activation of cognitive circuits, in particular, a structure that interprets a baby's cries and non-verbal clues, such as a squirm.
"These are regions that respond unconsciously to signs of an infants' needs, and that derive deep emotional reward from seeing the baby," Ms Feldman told the Telegraph.
She added that in gay fathers, but not heterosexual ones, the brain also had extra communication lines between emotional and cognitive structures. The more time a man spent as primary caregiver, the greater the connectivity, which suggested playing both parental roles caused the brain to integrate the structures required for each.
"Fathers' brains are very plastic," Feldman said, as reported by the Tech Times. "When there are two fathers, their brains must recruit both networks, the emotional and cognitive, for optimal parenting."
The findings, which were published in the Proceedings of the National Academy of Sciences, may add to the debate over whether gay men should be allowed to adopt children in certain areas of the US. Some states have banned gay couples from adopting, while other adoption agencies refuse to allow LGBT adoption.