To be fair, there may be other ways to explain their conclusions - and you might not need the clamps, harnesses and whips to replicate that kind of closeness (simply cooking a meal together might do the trick as well). Still, there is a stigma associated with S&M that critics are calling into question.
SPANKING is stressful at first, but it could bring consenting couples closer together. That's the implication of two studies of hormonal changes associated with sadomasochistic (S&M) activities including spanking, bondage and flogging.
link
http://www.reuniting.info/science/sex_in_the_brain