Oxytocin has been called "the cuddle hormone" or "the love hormone" due to its association with pair bonding. It appears to help reinforce the early attachment between mothers and their infants, as well as the bonds between romantic partners. Animal research has connected oxytocin (along with another hormone, vasopressin) with the lifelong pair-bonding of prairie voles, and scientists have reported increases in oxytocin levels following orgasm in humans. There is also evidence that increases in oxytocin may encourage prosocial behavior, though not all studies have found these positive results, and some experts have undercut the idea that the hormone is a “trust molecule.”