Sex and Violence "on/off" Switch Discovered

Scientists have known for some time that sexual and aggressive impulses are regulated by the diverse cluster of neurons located in the ventromedial hypothalamus (VMH), an ancient region of the brain conserved throughout mammalian evolution. However, recent studies have allowed scientists to pinpoint the exact location of these attack-promoting neurons and their role in the interplay between aggression and mating, effectively discovering an on/off switch for sex and violence.

The California Institute of Technology team, led by Dr. David Anderson, utilized a technique known as optogenetics. They injected into the the ventrolateral region of a mouse's VMH (VHMvl), the specific region associated with aggressive and sexual impulses, stunted viruses carrying a modified piece of DNA engineered to encode a photosensitive ion channel selective to blue light. When they recovered, the scientists were able to stimulate the mouse's VHMvl by exposing it to blue light. When stimulated, the [male] mouse indiscriminately attacked male, female, castrated male or anesthetized mice—and sometimes even a blown-up latex glove. Aggression ceased once the light stopped.

In a final experiment, where the VMHvl cells were genetically silenced, aggression was significantly reduced, suggesting that the VMHvl cells are indeed necessary for aggression to occur. The scientists concluded that this may explain how people are able to control bouts of "irrational, impulsive" anger by inhibiting the hypothalamus (possibly via descending fibers from the prefrontal contex).