Mice Have a Predatory Kill Switch in the Brain

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One specie in particular is known as the killer mouse for its habit of feeding on live pray, even other mice at times.

United States scientists have ramped up predatory behavior in mice by stimulating a region of the brain known for its role in emotions like fear and pleasure, according to a study published Thursday.

Without the latter set, de Araujo says, the mice pursued their prey but failed to "deliver the killing bite".

In the experiments, scientists shined the light directly on the animals' amygdalae and found that it caused them to tense the muscles in their neck and jaw.

Mice, which usually serve as prey for larger mammals, became threatening predators when researchers used a laser light to activate two sets of neurons in the amygdala - the area of the brain involved in emotions, behavior and motivation. And when the laser was on, the mice started to hunt everything around them.

However, it was noted that the mice only appeared to attack prey that was smaller than themselves - rather than launching an attack on the researchers.

'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 lead investigator Ivan de Araujo, Associate Professor of Psychiatry at the Yale University School of Medicine and an Associate Fellow at the John B Pierce Laboratory.

The Walking Dead analogy is fair only to a certain extent, says de Araujo.

The researchers suggest that predatory skills are what allowed jawed vertebrates to achieve evolutionary success, but they recognize that the neurological elements that permit such behavior are yet to be fully understood. So, he thought: "There must be some primordial sub-cortical pathway that connects sensory input to the movement of the jaw and the biting". When mice in empty cages had their amygdalas activated, they stopped whatever they were doing, positioned their front legs as if they were holding food and moved their mouths as if they were chewing. Predatory behavior refers to triggering complex motor actions. His lab had been looking at mice living and eating in cages. Now, though, they say they have documented a critical player in the process. Many areas were listed, but one responded nearly exclusively to hunting and not to eating. "I do however stress that the behaviour seems specific to hunting for food, so any effects would be associated with hunting activities, not aggression per se -for example against other humans".

By selectively manipulating the different types of neurons in this region, they found that one set of neurons controlled pursuit, and another controlled the kill. "They pursue the prey faster and they are more capable of capturing and killing it".

It has been supposed that there are submerged connections between the neurons and the neck and jaw muscles responsible for biting and killing.