Having a baby alters new mothers' brain activity, researchers have found, and a new study adds the first evidence of such changes in the brains of gay men raising children they adopted through surrogacy.

The men's pattern of brain activity resembles that of both new mothers and new fathers in the study.

The research, reported on Monday, could feed into the debate over whether gay men should be allowed to adopt children. Many U.S. adoption agencies will not work with same-sex couples, and some states prohibit them from adopting.

The current study, published in Proceedings of the National Academy of Sciences, was conducted in Israel, and builds on work by neuropsychologist Ruth Feldman of Bar-Ilan University and others, who showed that the brains of new mothers become hyperreactive to their child's cries and other emotional cues.

It was not clear if that pattern is a result of the hormonal and other changes that accompany pregnancy or a response to the experience of motherhood.