A study published in the Feb. 9 issue of Nature indicates that sex and violence are intertwined in the male brain. Deep within the brain of male mice is a circuit of cells that determine whether they fight or mate. Neuroscientists believe that human brains are wired similarly.
Stimulating sex drive and aggression
Measuring a certain cluster of neurons within the ventromedial hypothalamus (VMH) of male mice, Dr. Dayu Lin of New York University and Dr. David Anderson of the California Institute of Technology in Pasadena found that sexual behavior and violent behavior triggered that same part of the brain. Unstimulated, mice would ignore males they would normally attack. Activated via a mild, targeted electric pulse, the same mice would assault both inanimate objects and females they were courting.
Sex and fights cause same brain response
Expanding the study, Lin and Anderson’s team monitored the male test mice during encounters with male and female mice. Using a fluorescent tag that reveals which neurons are most active, the neuroscientists made the discovery that the same area of the VMH lit up during fights and sex.
Next, Lin and Anderson used optogenetic techniques in which they inserted a gene into the test mice’s brains that made them susceptible to blue light. With the light, the scientists could fire the neurons in question on demand. Blue light activation prompted aggression, but if the mice were already in the middle of a sex act, the blue light had no observable effect.
“It’s kind of in its own world. It doesn’t listen to anything else,” Dr. Lin said.
Sex and violence: A natural link
Dr. Clifford Saper of Harvard Medical School points out that sex and violence are inseparably linked in a chain that leads to the survival of a species. The mice fought off invading males to preserve territory, and they had sex with females to pass on their genetic line. Even in humans, stimulation of the VMH is known to produce aggressive behavior. Dr. Newton Canteras of the University of São Paulo in Brazil believes further study will reveal that sexual behavior is centered in the same area of the human hypothalamus. Such knowledge may also help scientists understand and treat violent sex criminals.
Scientific American: http://www.scientificamerican.com/article.cfm?id=sex-and-violence-linked
Know your sexy, fighting hypothalamus
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