4.15.2004
today is my birthday
from the ny times
Sex and the Brain: Researchers Say, "Vive la Différence!"
March 16, 2004
By ANAHAD O'CONNOR
For almost a decade, researchers at Pfizer struggled to
show that Viagra, the male impotence drug, could enhance
sexual function in women.
Last month, they gave up.
Countless tests on thousands of women made it clear that
the little blue pill, though able to stir arousal, did not
always evoke sexual desire.
Viagra's failure underscored the obvious: when it comes to
sexuality, men and women to some extent are differently
tuned. For men, arousal and desire are often intertwined,
while for women, the two are frequently distinct.
Scientists have recently begun to map out how this
difference shows up in the brain.
For example, male arousal, studies find, is strongly
visual, and when men engage in sexual activity or even
anticipate it, brain structures once thought to have little
connection to sex spring into action. The same brain
regions, however, remain relatively quiet when women are
aroused.
At the core of the sexual divide, some researchers say, is
the amygdala, an almond-shaped nugget embedded in the
limbic system, the brain's seat of emotions. Once thought
to be involved exclusively with emotions like fear and
anger, the amygdala is now believed to be more complicated.
In one recent study, a team of researchers at Emory
University had 28 men and women look at erotic photographs
while an M.R.I. took snapshots of their brains. A pattern
immediately emerged. The photographs set off a frenzy of
brain activity, particularly in the amygdalae of men. Yet
the two groups reported equal arousal most of the time.
"This definitely emphasizes that up until recently the
amygdala has been overlooked," said Dr. Stephan Hamann, a
professor of psychology and the lead author of the study,
which was published online by Nature Neuroscience last week
and is scheduled to appear in the journal in April. "Often,
the amygdala is involved in the anticipation of positive
emotions, which this parallels nicely with."
Much of the insight into the amygdala's role in
anticipating sex, and possibly other pleasant emotions,
stems from research on animals.
In a study in 1989, scientists trained caged male rats to
gain access to females by pushing a lever. The researchers
then destroyed part of the amygdala. The rats lost interest
in pressing the lever. Yet despite this lack of motivation,
they had no problem engaging in sexual intercourse when the
females were placed in their cages.
Other studies have gone further. In a study published last
year, researchers in the Netherlands recorded brain
activity in men as their female partners brought them to
orgasm.
The amygdala, the scientists found, showed decreased
activity during climax. Other studies have suggested that a
larger amygdala may lead to a more robust sex drive.
Dr. Hamann pointed out that the amygdala is known to have
intricate connections to primates' visual systems. One
reason for the powerful response to visual stimuli in men,
he said, could be cultural. Men tend to be inundated with
sexual imagery and, possibly, are more likely to seek it
out.
Evolution may also have a role. Some experts argue that,
over time, men naturally became more dependent than women
on sight in selecting a mate.
"For millions of years, men have had to size up a woman's
reproductive capacity by looking for signs of youth and
health that would enable them to carry a healthy baby,"
said Dr. Helen Fisher, an anthropologist at the Center for
Human Evolutionary Studies at Rutgers, and the author of a
recently published book, "Why We Love: The Nature and
Chemistry of Romantic Love."
Dr. Fisher has studied the brains of people in the early
stages of romance. For a man, she found, pictures of a new
partner light up parts of the brain involved in visual
processing and arousal. But women, she noticed, show more
activity in areas linked to reward, emotion and attention.
"Men, despite what most people think, fall in love faster
than women do, probably because they're so visual," Dr.
Fisher said.
Women, on the other hand, may be more attuned to the signs
that a man will make a good father or provider, she added,
though some other researchers find this assertion dubious.
A woman's choice of a mate, Dr. Fisher argues, could
involve an interplay among a number of factors, including,
some experts now theorize, a man's odor.
Several years ago, Swiss scientists discovered that women
could sniff out genetic differences in potential mates.
When women were asked to smell T-shirts that different men
had worn, they often ranked more favorably the shirts that
belonged to men with dissimilar genes for major
histocompatibility complex, a group of proteins involved in
immunity to disease. The odors a woman preferred also
tended to remind her of past and current partners.
Seeking out different immune-system genes might be a way to
prevent inbreeding or to arm offspring with a more
versatile immune system, said Dr. Rachel S. Herz, a
psychologist at Brown who in a study in 2002 found that
women ranked body odor above almost every other factor in
attraction, except "pleasantness."
"For women, the costs of pregnancy like time and energy are
pretty high," Dr. Herz said. "So to balance those costs,
you want to make sure the child is going to live. And what
is indicative of how healthy you are is your immune system,
which is manifested in your smell."
Yet to play down the role of visual stimulation for women
would be unwise, researchers say, and female admirers of
Brad Pitt or George Clooney would probably agree. In
research last year at Northwestern, Dr. Meredith Chivers,
demonstrated that women could sometimes have more powerful
responses to visual stimuli than men, although in different
ways.
In her study, which ignited a small firestorm, Dr. Chivers
used a device to measure genital arousal in subjects as
they looked at pornography. Heterosexual men, she found,
were aroused by footage of men and women having sex. Gay
men reacted to two men having sex. Women, regardless of
sexual orientation, responded to everything.
In some cases, she said, women reported no sexual arousal,
though the device said otherwise.
"One of the fascinating things was that the female
responses to sexual images were fast and automatic," said
Dr. Chivers, who is now at the Center for Addiction and
Mental Health in Toronto. "The fact that they were not
always aware speaks to there being other factors involved
like emotion and psychological influences."
What is apparently a disconnection between female arousal
and desire, researchers note, squares nicely with the
Pfizer findings on Viagra.
Still, other experts point out that it is impossible to
define neatly or predict how men and women will respond.
People's perceptions are colored by their personal
experiences, said Dr. Leonore Tiefer, a sex therapist who
is a clinical associate professor of psychiatry at the New
York University medical school.
"Differences between genders are boring," Dr. Tiefer said.
"The big differences are within the sexes, between
individuals. It is not the case that every person pays
attention to the same thing.
"It's like everything else in life - eating, dancing,
traveling. The whole experience is shaped by your history
and by what you're paying attention to."
http://www.nytimes.com/2004/03/16/health/16SEX.html?ex=1081686374&ei=1&en=47836e278027b046
10:32
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bubbly and lovely: i'm too poor for therapy.
