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Oxytocin, aka the "hormone of love" or "cuddle chemical," is a mammalian hormone that is released during labor and breastfeeding; in these contexts it induces uterine contractions and milk letdown. But it is perhaps better known for its alleged role in attachment bond formation.

The attachment bond between a mother and infant is essential to species survival; without it, a mother might not be disposed to care for her dependent newborn and said newborn would probably not live long enough to reproduce. The attachment bond can also color all future relationships the infant will go on to develop in life.

Despite its importance, very little is known about the biochemical underpinnings of attachment bond formation and maintenance in humans. Oxytocin is known to be involved in the process in animals, like mice and prairie voles, but its role in human bond formation had never been tested. So scientists just tested it, and found that oxytocin strengthened whatever feelings about their mothers adult males already had.

The study subjects were 31 men between the ages of 19 and 45. Women were not included because of the aforementioned effect of oxytocin: it induces labor. The men were given oxytocin or a placebo intranasally, and then asked to lie on a couch and talk about their mothers with a bearded doctor smoking a pipe. OK, just kidding about the couch part. And the pipe. They were actually asked to fill out questionnaires assessing their recollections of maternal care and closeness, two key features of the attachment bond.

In animals, oxytocin is involved in linking social stimuli (i.e. your mother's face) with hedonic information (like feeling comforted and happy, or not). The researchers hypothesized that if the same were the case in humans, then oxytocin would not have the absolutely positive lovey-dovey affects commonly attributed to it. Rather, it would intensify the attachment representations already present in the men's minds.

Those who had adequate maternal responsiveness and closeness would be positively affected by oxytocin. But those who had attachment anxiety - their mothers let them cry in their cribs too long, so they were, and continue to be, obsessed with confirming the affections of their caregiver and afraid of being abandoned - would be negatively affected by the oxytocin.

This is exactly what they found. Men with strong bonds as assayed by a questionnaire at the start of the study remembered being closer to their mothers after sniffing the oxytocin than the placebo, while the anxiously attached men remembered their mothers being less caring after getting the oxytocin than the placebo. All of the men got the hormone once and the placebo once, and they did a terrible job of guessing which one they got when, so the study was adequately blinded.

To ensure the specificity of oxytocin's effects on the attachment bond, the men were also given surveys to assess their moods and other relationships, and these showed that oxytocin had no effect on the men's moods, opinions about themselves, or their other current attachments.

Based on these results, the researchers' current working hypothesis is that oxytocin activates, or primes, the attachment system already in place. They think that it made the study participants selectively remember information about their mothers that is in keeping with their attachment style, but it did not make them feel more attached. So it is not really the "hormone of love;" it is more like the hormone of "see mom, I was right all along."