A study involving men and their mothers suggests a new function for the "love hormone" oxytocin in human behaviour.
Men who inhaled a synthetic form of oxytocin, a naturally occurring chemical, recalled intensified fond memories of their mothers if, indeed, mom was all that caring.
But if men initially reported less close relationships with Mom, oxytocin seemed to encourage them to dwell on the negative.
These findings, published in the journal Proceedings of the National Academy of Sciences, appear to contradict public perception about oxytocin's beneficial effects, the researchers say.
"There's a popular idea that oxytocin has these ubiquitous positive effects on social interactions, but this suggests that it depends on the person to whom it's given and the context in which it's given," said study lead author Jennifer Bartz. "It's not this universal attachment panacea."
Another expert agreed.
Oxytocin makes memory stronger
"People were thinking that oxytocin was going to generally make things more positive but depending on how someone's attachment really was, it just made the memory of that come back stronger," said Keith A. Young, vice chair for research in the Department of Psychiatry and Behavioral Science at the Texas A&M Health Science Center College of Medicine in Temple.
"The oxytocin seemed to tap into the actual memory rather than making everything better."
Oxytocin, which is produced in abundance when a mother breast-feeds her baby, is known as the "bonding" hormone and may actually have therapeutic applications.
One study found that people with high-functioning autism or Asperger's syndrome were better able to "catch" social cues after inhaling the hormone.
Oxytocin has also been linked to trust, empathy and generosity, but may also spark the less attractive qualities of jealousy and gloating. By fostering attachment, oxytocin is considered critical to survival of an individual, and also to survival of the species.
"It's what allows the infant to survive to maturity and to reproduce by ensuring the caregiver stays close to the infant and provides nurturance and support to an otherwise defenseless infant," explained Bartz, assistant professor of psychiatry at Mount Sinai Medical Center in New York City.
How the study was done
Those initial experiences with an early caregiver - usually a mother - stay with us and guide our later relationships, for better or for worse.
The researchers hypothesised that oxytocin would amplify whatever initial memories men had about their mothers, and this turned out to be accurate.
Thirty-one men, aged 19 to 45, were asked about the care they had received from their mothers during childhood, based on their own recollections
The men also made two visits to the clinic, about a month apart, once to receive oxytocin and once to receive a placebo. In effect, each man acted as his own control group.
Men who had initially described their mothers as warm and nurturing tended to think even more highly of them after receiving the oxytocin.
But men who hadn't reported such positive connections actually downgraded their assessment of the maternal relationship after taking oxytocin.
Hormone involved with human attachment
"We found that participants who were more securely attached, when they got oxytocin, they remembered mom as more close," Bartz said. "For those who were more anxiously attached, it amplified it in the other direction. It brought to mind their chronic insecurities about their relationship with their mother.
"This supports this idea that oxytocin may actually play a role in the formation of these memories," she added.
"It's not just a 'happy' drug," said Paul Sanberg, distinguished professor of neurosurgery and director of the University of South Florida Center for Aging and Brain Repair in Tampa. "Because oxytocin differentiates like that [between pleasure and anxiety], it's more evidence that it's involved in human attachment. This is the first empirical evidence."
Most of the evidence we have so far on oxytocin as an attachment hormone has been in animals, noted Sanberg, who was not involved with the study.
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