I was going to cover this paper, but Ed beat me to it (and did a far better job than I would have):
With a pulse of light, Dayu Lin from New York University can turn docile mice into violent fighters - it's Dr Jekyll's potion, delivered via fibre optic cable. The light activates a group of neurons in the mouse's brain that are involved in aggressive behaviour. As a result, the mouse attacks other males, females, and even inanimate objects.
Lin focused on a primitive part of the brain called the hypothalamus that keeps our basic bodily functions ticking over. It lords over body temperature, hunger, thirst, sleep and more. In particular, Lin found that a small part of this area - the ventrolateral ventromedial hypothalamus (VMHvl) - acts as a hub for both sex and violence.
And the discovery that this portion of the brain controls bot sex and violence has many deep implications for how psychologists study an array of sexual behavarioral disorders.
And here we are at the punchline of a story in Analog from the 60s: the announcement that research had finally proven that it's just not possible to "Make love, not war."
@D.C. - I'm not so sure. On of the amazing things they discovered is that while the mice were having sex, they couldn't induce agression. Using the neurons for sex actually inhibited the violent behavior.
@Vinay - maybe it means they're not really disorders.