Two sets of neurons have been identified in the amygdala that, when activated, can turn mice into highly effective killers, a new study reports. The findings could help determine how hunting behavior evolved, hundred of millions of years ago.

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Here’s one the conspiracy theorists will love.

A team from Yale university have managed to hack the brains of mice into highly efficient killing machines. They ramped up the animals’ aggression by activating two sets of neurons in their amygdala, the paper states.

“The animals become very efficient in hunting,” says Ivan de Araujo, associate professor of psychiatry at Yale University and an associate fellow at The John B. Pierce Laboratory in New Haven.

“They pursue the prey [a live cricket] faster and they are more capable of capturing and killing it.”

Tampering with these neurons caused the mice to attack even inanimate objects — sticks, bottle caps, and an insect-like toy. Dr De Araujo says that the animals bit the toy “intensively” and even used “their forepaws in an attempt to kill it.”

Bloodlust, but with manners

The mice saved their aggressiveness only for prey, as De Araujo reports that the furry rodents didn’t attack one another even with both sets of neurons activated. These results offer a glimpse into how the brain changed hundreds of millions of years ago when jaws first developed. It was the first time any brain had an efficient tool with which to kill prey, a change that “must have influenced the way the brain is wired up in a major way,” De Araujo says.

Just like the military has a chain of command to make sure everything is where it’s supposed to be in battle, brains needed to re-wire to allow for specialized hunting circuits. These serve to govern and coordinate the movements of predators’ jaws and neck muscles, turning a clumsy beast into a deadly predator.

“This is a very complex and demanding task,” De Araujo says.

The team used mice since we know these animals are predatory — they hunt and eat whatever they can, really, mostly insects and worms. One species, in particular, is known as the killer mouse for its habit of feeding on live prey, even other mice at times.

By watching brain scans of hunting mice, they discovered one set of neurons that activated when chasing prey and another that would flare up when biting or killing something. Both of these bundles of neurons are located in the amygdala, which is involved in regulating emotion and motivation.

The next step was to use optogenetics to create mice in which these sets of neurons could be activated using a laser.

“When we stimulate [both sets of] neurons […] they assume the body posture and actions usually associated with real hunting

“It is as if there is a prey in front of the animal,” De Araujo says.

The team found evidence of similar “hunting circuits” in other species that relied on hunting to survive — including humans.

Knowing how the brain processes hunting and killing gives us a glimpse of how — and when — these behaviors evolved. It might also help us understand how aggression, in general, is handled by the brain.

The paper “Integrated Control of Predatory Hunting by the Central Nucleus of the Amygdala” has been published in the journal Cell.

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