The burgeoning field of optogenetics—using shot of light on neurons to control behavior—has already produced some intruiging and peculiar results. Now add one more: Scientists can use it to make mice angry and aggressive.
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.
A spike in testosterone may not always turn you into a greedy, aggressive, power hungry monster. According to research led by Ernst Fehr, testosterone’s true effect may be to encourage status-seeking behavior, and it can actually make people play more fairly with others.
What’s more, its biological effects on a person may be overruled by that person’s beliefs. In a game-playing experiment set up by Fehr in which some people received a testosterone shot while others got a placebo, those who suspected they had received bona fide testosterone acted more selfishly than those who believed they got the bogus treatment, no matter what they actually received [New Scientist].
Fehr and colleagues used the ‘ultimatum bargaining’ game to test how testosterone would affect behaviour in a group of 121 women. Counter-intuitively, women who were given testosterone bargained more fairly. But the idea that testosterone causes aggression in humans, as it clearly does in rodents, is so firmly ingrained in the human psyche that women who believed they had been given testosterone — whether or not they had — bargained much less fairly [Nature News]. The researchers tested women because they have little variation in their normal testosterone levels. The authors, who published their work in the journal Nature, say their results essentially debunk the popular wisdom that says testosterone causes aggression. Rather, their findings reinforce another idea–hormones are complicated, and testosterone is no exception.
80beats is DISCOVER's news aggregator, weaving together the choicest tidbits from the best articles on the day's most compelling topics.
80beats is written by Veronique Greenwood and Valerie Ross. This team darts through each day's science news faster than the ruby-throated hummingbird that beats its wings 80 times per second. Send ideas, tips, suggestions, and complaints to [azeeberg at discovermagazine dot com].
A spike in 
