January 6, 2011
The work was
authored by Shani Gelstein, Yaara Yeshurun, Liron
Rozenkrantz, Sagit Shushan, Idan Frumin, Yehudah Roth
and Noam Sobel, was conducted in collaboration with the
Edith Wolfson Medical Center, Holon.
Prof. Noam Sobel’s research is supported by the James S.
McDonnell Foundation 21st Century Science Scholar in
Understanding Human Cognition Program; the Minerva
Foundation; the European Research Council; and Regina
The Weizmann Institute of Science in Rehovot, Israel, is
one of the world's top-ranking multidisciplinary
research institutions. Noted for its wide-ranging
exploration of the natural and exact sciences, the
Institute is home to 2,600 scientists, students,
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efforts include the search for new ways of fighting
disease and hunger, examining leading questions in
mathematics and computer science, probing the physics of
matter and the universe, creating novel materials and
developing new strategies for protecting the
Emotional crying is a universal, uniquely human behavior.
When we cry, we clearly send all sorts
of emotional signals. In a paper published online today in Science
Express, scientists at the Weizmann Institute have demonstrated that
some of these signals are chemically encoded in the tears
themselves. Specifically, they found that merely sniffing a woman’s
tears - even when the crying woman is not present - reduces sexual
arousal in men.
Humans, like most animals, expel various compounds in body fluids
that give off subtle messages to other members of the species. A
number of studies in recent years, for instance, have found that
substances in human sweat can carry a surprising range of emotional
and other signals to those who smell them.
But tears are odorless.
In fact, in a first experiment led by
Shani Gelstein, Yaara Yeshurun and their colleagues in
the lab of Prof. Noam Sobel in the Weizmann Institute’s
Neurobiology Department, the researchers first obtained emotional
tears from female volunteers watching sad movies in a secluded room
and then tested whether men could discriminate the smell of these
tears from that of saline. The men could not.
In a second experiment, male volunteers sniffed either tears or a
control saline solution, and then had these applied under their
nostrils on a pad while they made various judgments regarding images
of women's faces on a computer screen.
The next day, the test was repeated -
the men who were previously exposed to tears getting saline and vice
versa. The tests were double blinded, meaning neither the men nor
the researchers performing the trials knew what was on the pads. The
researchers found that sniffing tears did not influence the men's
estimates of sadness or empathy expressed in the faces.
To their surprise, however, sniffing
tears negatively affected the sex appeal attributed to the faces.
To further explore the finding, male volunteers watched emotional
movies after similarly sniffing tears or saline. Throughout the
movies, participants were asked to provide self-ratings of mood as
they were being monitored for such physiological measures of arousal
as skin temperature, heart rate, etc. Self-ratings showed that the
subjects’ emotional responses to sad movies were no more negative
when exposed to women’s tears, and the men “smelling” tears showed
no more empathy.
They did, however, rate their sexual
arousal a bit lower.
The physiological measures, however,
told a clearer story. These revealed a pronounced tear-induced drop
in physiological measures of arousal, including a significant dip in
testosterone - a hormone related to sexual arousal.
Finally, in a fourth trial, Sobel and his team repeated the previous
experiment within an
fMRI machine that allowed them to
measure brain activity. The scans revealed a significant reduction
in activity levels in brain areas associated with sexual arousal
after the subjects had sniffed tears.
“This study raises many interesting
questions. What is the chemical involved? Do different kinds of
emotional situations send different tear-encoded signals? Are
women’s tears different from, say, men's tears? Children’s
This study reinforces the idea that
human chemical signals - even ones we’re not conscious of -
affect the behavior of others.”
Human emotional crying was especially
puzzling to Charles Darwin, who identified functional antecedents to
most emotional displays - for example, the tightening of the mouth
in disgust, which he thought originated as a response to tasting
But the original purpose of emotional
tears eluded him.
The current study has offered an answer
to this riddle:
Tears may serve as a chemosignal.
Sobel points out that some rodent tears
are known to contain such chemical signals.
"The uniquely human behavior of
emotional tearing may not be so uniquely human after all,” he