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More Evolved Brain Region Controls Sex Urges

Arousal based in more primitive area

THURSDAY, Nov. 29, 2001 (HealthDayNews) -- As most teen-age boys know, it's not easy to keep hormones in check. While humans can control their level of sexual excitation with some effort, a new study suggests that skill is a fairly recent gift from evolution.

By studying men watching pornographic videos, researchers in Canada have pinpointed areas of the brain that become active when the men tried to avoid being stimulated. In evolutionary terms, these regions of restraint are newer than the more primitive areas where the sexual urges arise in the first place.

The findings offer more than just a glimpse at how the mind deals with sex, says study co-author Mario Beauregard, an associate researcher at the University of Montreal. "The most important message [of the research] is that a human being … has the capacity to consciously and voluntarily influence his own cerebral activity -- electrical and chemical brain processes. Undoubtedly, this represents one of the most remarkable human faculties that have emerged in the course of human evolution."

Only primates have prefrontal cortexes. That region of the brain, located right behind the forehead, is most advanced in humans and is involved in analytical thinking, multitasking and problem solving.

Beauregard says the purpose of the study was to investigate how the brain regulates itself by controlling emotion. Some experts suspect that lesions in the prefrontal cortex may be responsible for abnormal behavior in people, and some think breakdowns in the brain circuitry responsible for self-regulation could cause depression and anxiety, he says.

Beauregard and his colleagues enrolled 10 healthy white men, aged 20-42. The men watched excerpts of pornographic films that, in most cases, showed heterosexual or lesbian group sex.

Researchers measured brain activity of the men in two situations -- when they were told to let themselves be sexually aroused and when they were directed to control their urges and act as though they were "detached observers."

The findings appear in a recent online edition of the Journal of Neuroscience.

The men's prefrontal cortexes, the newer regions of their brains, turned on when they tried to control themselves. By contrast, erotic feelings prompted activity in older parts of the brain, including the region known as the limbic system, and the neocortex, which allows people to be aware of their feelings, Beauregard says.

The study, in effect, examined how the mind suppresses feelings on the borderline between voluntary and involuntary, says Dr. Thomas Lewis, professor of psychiatry at the University of California at San Francisco. Part of the challenge is that "no one has any idea how free will exists [in the brain]," he says.

It's not surprising that the prefrontal cortex becomes active when men try to hold in their sexual arousal, Lewis says. That area appears to be in charge of inhibition, and people who suffer from injuries to that region have problems suppressing inappropriate thoughts and emotions.

"They pretty much act on the spur of the moment. They say and do things that are inappropriate," Lewis says.

If that sounds a bit like a teen-age boy, there's a reason. The prefrontal cortex develops in adolescence and that could explain why adults usually control themselves better than children, Beauregard says.

In other words, as your brain grows, so does your ability to keep your feelings to yourself.

What To Do

How does your brain work? Turn to howstuffworks.com for the inside story. This Scientific American article describes how the prefrontal cortex influences how we think.

Curious about how the brain looks? Check these human brain pictures.

And here are some pinups and explanations of the limbic system.

SOURCES: Interviews with Mario Beauregard, Ph.D., associate researcher, University of Montreal; Thomas Lewis, M.D., psychiatrist and assistant clinical professor of psychiatry, University of California San Francisco School of Medicine, San Francisco, co-author of A General Theory of Love; September 2001 Journal of Neuroscience
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