Scientists turn mild-mannered mice into killers （517 words）

By Clive Cookson, Science Editor

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Step aside killer zombies: scientists have delved deep into ancient brain circuits to reveal neurons that can instantly turn mild-mannered mice into ferocious predators — before switching the rodents back to their normal placid selves.

The researchers at Yale University used “optogenetic” technology, which switches specific neurons on and off in genetically engineered animals with laser light, to tap into brain mechanisms that control predatory hunting.

“We’d turn the laser on and they’d jump on an object, hold it with their paws and intensively bite it as if they were trying to capture and kill it,” said Ivan de Araujo, lead investigator.

The mice attacked not only live prey such as crickets, which they immediately devoured, but also inanimate objects such as mobile plastic toys that they would normally avoid.

The study, published in the journal Cell, was part of a broader programme to research the evolutionary biology and neural mechanisms underlying feeding behaviour in animals.

Investigation of various brain regions showed that the central nucleus of the amygdala was closely associated with the urge to hunt and with controlling the jaw and neck muscles required to subdue and kill prey.

By manipulating brain cells in this region through optogenetics, the Yale team found one distinct set of neurons controlled pursuit and another controlled the kill. If the hunting neurons were switched on and the biting set inactivated, the mice pursued prey but could not deliver the killer bite to finish it off.

The next stage in the Yale project will be to explore how sensory inputs (from the eyes, nose and ears) into the amygdala trigger predatory behaviour and to discover how the brain co-ordinates its pursuit and killing modules.

“We now have a grip on their anatomical identities, so we hope we can manipulate them even more precisely in the future,” said Dr de Araujo.

The brain mechanisms involved may be ancient. The evolution of jaws in vertebrates, starting with fish about 400m years ago, has been driven by carnivores.

“The ability to hunt was a major evolutionary advantage,” said Dr de Araujo. “The first mammals were specialist insectivores and these traits are still present in their descendants today.”

The Yale research could have practical applications, such as using improved knowledge of the brain’s motor circuits that control face and jaw muscles to treat neurological diseases.

Researchers in mobile robotics and artificial intelligence could also use information from the predatory brain to create a device that pounces on a moving target, Dr de Araujo added. But the production of killer zombie mice is not on the agenda.