Oxytocin is released into the bloodstream to produce its classic
effects on the uterus and breast milk, but it is also released
into defined regions of the brain that are involved in
emotional, cognitive, and social behaviors.
One review of the evidence says oxytocin "has attracted intense
attention" after the discovery of its "amazing variety of
behavioral functions." The review, by Inga Neumann, says
oxytocin has an impact on "pro-social behaviors" and emotional
responses that contribute to:
Relaxation
Trust
Psychological stability.
However, another review notes that the hormone does not act
alone in the chemistry of love, but is "just one important
component of a complex neurochemical system that allows the body
to adapt to highly emotive situations."
Another review has also sounded caution, calling for research to
look more to the general effects than to the specific effects of
oxytocin that are being interpreted. "After all, it is rather
unlikely that any widely acting hormone or neurotransmitter will
be narrowly funneled to modulate complex, high-order mental
processes that are specific to social cognition," say the
authors of a 2013 paper.
Scientific research has nonetheless uncovered brain oxytocin's
specific ability to modulate social behavior, including effects
on motherly care and aggression, bonding between couples, sexual
behavior, social memory, and trust. Brain oxytocin also reduces
stress responses, including anxiety - and these anxiolytic
effects have been demonstrated in a number of species.
One of the so-called 'love hormone' studies was published in
2012, and it examined oxytocin levels in new lovers versus those
in single people. It found that there were high levels of the
hormone in the first stages of romantic attachment, and these
were sustained for six months. A stream of studies in the last
decade have focused on oxytocin's effects on body and mind.
Here's a look at what we've learned.
Pregnant women with higher levels of oxytocin during their first
trimester bonded more strongly with their babies after they were
born, according to a 2007 study in the journal Psychological
Science. And compared with other women, women with higher levels
throughout their pregnancy and in the first month after birth
reported engaging in more behaviors such as singing, feeding and
bathing their infants in specific ways that promoted an
exclusive relationship between the two, the study found.
Comparing urine levels of oxytocin and a related hormone called
vasopressin in biological and adoptive children who lived in
Russian and Romanian orphanages, researchers found that oxytocin
rose in biological children after having contact with their
mothers. The study, published in 2005 in the journal Proceedings
of the National Academy of Sciences, showed that oxytocin levels
remained static in the adoptive children in the same situation,
suggesting a physiological basis for why some adoptive children
have difficulty forming secure relationships.
Research done on prairie voles showed that those separated from
their siblings exhibited signs of anxiety, stress and depression
that abated after they were injected with oxytocin.
The study, presented at a 2007 meeting of the Society for
Neuroscience, indicated the hormone's effects were more evident
under stressful situations.
A November study in the journal Proceedings of the National
Academy of Sciences supported researchers' theory that oxytocin
would amplify men's early memories of their mothers. In a group
of 31 men, those who inhaled a synthetic version of the hormone
found the hormone intensified fond memories of their mothers if
their relationships had been positive. Those whose ties with
their mom's had frayed downgraded their opinions after inhaling
oxytocin, the study showed.
In its best understood role, oxytocin is released in large
amounts during labor, intensifying the uterine contractions that
open the cervix and allow the baby to pass through the birth
canal. Physicians have been using synthetic oxytocin, also known
by its brand name Pitocin, to induce or augment labor since the
early 1900s. After birth, the hormone continues to stimulate
uterine contractions that discourage hemorrhaging, and more is
released when the nipples are stimulated during suckling,
promoting the letdown of milk into the nipples.
Spontaneous erections in rats were observed after oxytocin was
injected into their cerebrospinal fluid in a 2001 study in the
journal Physiological Review. And a cocktail of brain chemicals
that includes oxytocin is released in men during ejaculation.
These chemicals can intensify bonding between sexual partners ,
though, Ellison noted, "it isn't the same for everyone."
"I think there is a variability," said Ellison, who also teaches
sexuality classes to health professionals. "For people who can
really get into the sensuousness of hugging and cuddling, that
is the hormone released in this process. For people who don't
get into it, maybe they're not releasing the oxytocin. It may be
a circular thing."
According to a 1999 article in the journal Progress in Brain
Research, some studies indicate that oxytocin inhibits tolerance
to addictive drugs, including opiates, cocaine and alcohol , and
reduces withdrawal symptoms. "It's an antidote to craving,"
Ellison explained. "That craving (for drugs), that hunger, is
probably eased with this hormone. It's involved with the
satisfaction of hunger."
A February study in the journal Proceedings of the National
Academy of Sciences showed that inhaling oxytocin significantly
improved the ability of people with autism to interact with
others. Previous studies indicated natural oxytocin levels were
lower in those with autism, a developmental disorder
characterized by difficulties in communication and social
relationships. Oxytocin also reduced autistic individuals' fear
of others, researchers said.
A June study in the journal Science suggested oxytocin triggers
defensive aggression against outsiders who might threaten
someone's social group, such as in soldiers who defend their
comrades. Prior animal studies had shown that the hormone
promotes protectionist behavior, but this research was the first
to demonstrate a similar effect in humans.
Oxytocin released in the brain under stress-free conditions
naturally promotes sleep , according to a 2003 study in the
journal Regulatory Peptides. Ellison said this link makes sense
because oxytocin counters the effects of cortisol, which is the
known as the stress hormone. "It has a calming effect," she
said. "It leaves you feeling tranquil and loving, and certainly
that helps our path to sleep."
In a 2007 study in the journal Public Library of Science ONE,
participants inhaled oxytocin or a placebo through their noses,
and then were given a decision on how to split money with a
stranger. Those on oxytocin were 80 percent more generous,
researchers said, and the hormone seemed to affect their sense
of altruism as well.
Oxytocin: the monogamy hormone. This study, published in the
journal PNAS in November 2013, examined brain scans of men who
had received oxytocin or placebo via a nasal spray. The oxytocin
was associated with activation of the men's reward centres in
their brains, and with greater feelings of attraction to their
partners versus other women in photographs. This followed a very
similar study in The Journal of Neuroscience in November 2012: A
hormone can help keep men faithful.
High oxytocin levels "trigger oversensitivity to emotions of
others." Released in January 2014, this study in Emotion found
that people receiving oxytocin nasal spray saw facial expression
of emotions in others more intensely.
Oxytocin makes you feel more extroverted. This 2011 research
paper in Psychopharmacology gave results from intranasal
oxytocin improving self-perception in social situations,
amplifying personality traits such as warmth, trust, altruism
and openness. The hormone that allows us to love may also
encourage us to lie. This 2014 study found participants given
oxytocin were more likely to lie for the benefit of the group.
With so many studies done and still going on, oxytocin the "love
hormone" still remains to be fully understood and explored. But
the above discussions goes a long way in demystifying its
secrets and its effect in human beings.
Oxytocin's effects on emotion
Oxytocin released in the brain under stress-free conditions
naturally promotes sleep , according to a 2003 study in the
journal Regulatory Peptides. Ellison said this link makes sense
because oxytocin counters the effects of cortisol, which is the
known as the stress hormone. "It has a calming effect," she
said. "It leaves you feeling tranquil and loving, and certainly
that helps our path to sleep."