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One step closer to SOMA
06-05-2009, 04:27 AM,
One step closer to SOMA
ScienceDaily (June 3, 2009) — Why does dishing with a girlfriend do
wonders for a woman's mood?

A University of Michigan study has identified a likely reason: feeling
emotionally close to a friend increases levels of the hormone
progesterone, helping to boost well-being and reduce anxiety and

"This study establishes progesterone as a likely part of the
neuroendocrine basis of social bonding in humans," said U-M researcher
Stephanie Brown, lead author of an article reporting the study
findings, published in the current (June 2009) issue of the
peer-reviewed journal Hormones and Behavior.

A sex hormone that fluctuates with the menstrual cycle, progesterone
is also present in low levels in post-menopausal women and in men.
Earlier research has shown that higher levels of progesterone increase
the desire to bond with others, but the current study is the first to
show that bonding with others increases levels of progesterone. The
study also links these increases to a greater willingness to help
other people, even at our own expense.

"It's important to find the links between biological mechanisms and
human social behavior," said Brown, is a faculty associate at the U-M
Institute for Social Research (ISR) and an assistant professor of
internal medicine at the U-M Medical School. She is also affiliated
with the Ann Arbor Veterans Affairs Hospital. "These links may help us
understand why people in close relationships are happier, healthier,
and live longer than those who are socially isolated."

Progesterone is much easier to measure than oxytocin, a hormone linked
to trust, pair-bonding and maternal responsiveness in humans and other
mammals. Oxytocin can only be measured through an invasive spinal tap
or through expensive and complex brain imaging methods, such as
positron emission tomography scans. Progesterone can be measured
through simple saliva samples and may be related to oxytocin.

In the current study, Brown and colleagues examined the link between
interpersonal closeness and salivary progesterone in 160 female
college students.

At the start of the study, the researchers measured the levels of
progesterone and of the stress hormone cortisol in the women's saliva,
and obtained information about their menstrual cycles and whether they
were using hormonal contraceptives or other hormonally active

To control for daily variations in hormone levels, all the sessions
were held between noon and 7 p.m.

The women were randomly assigned to partners and asked to perform
either a task designed to elicit feelings of emotional closeness or a
task that was emotionally neutral.

In the emotionally neutral task, the women proofread a botany
manuscript together.

After completing the 20-minute tasks, the women played a computerized
cooperative card game with their partners, and then had their
progesterone and cortisol sampled again.

The progesterone levels of women who had engaged in the emotionally
neutral tasks tended to decline, while the progesterone levels of
women who engaged in the task designed to elicit closeness either
remained the same or increased. The participants' cortisol levels did
not change in a similar way.

Participants returned a week later, and played the computerized card
game with their original partners again. Then researchers measured
their progesterone and cortisol. Researchers also examined links
between progesterone levels and how likely participants said they
would be to risk their life for their partner.

"During the first phase of the study, we found no evidence of a
relationship between progesterone and willingness to sacrifice," Brown
said. "But a week later, increased progesterone predicted an increased
willingness to say you would risk your life to help your partner."

According to Brown, the findings are consistent with a new
evolutionary theory of altruism which argues that the hormonal basis
of social bonds enables people to suppress self-interest when
necessary in order to promote the well-being of another person, as
when taking care of children or helping ailing family members or

The results also help explain why social contact has well-documented
health benefits---a relationship first identified nearly 20 years ago
by U-M sociologist James House.

"Many of the hormones involved in bonding and helping behavior lead to
reductions in stress and anxiety in both humans and other animals. Now
we see that higher levels of progesterone may be part of the
underlying physiological basis for these effects," Brown said.

Adapted from materials provided by University of Michigan.

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