Mice have a switch in the brain that turns on their killer instincts, and researchers from Yale University have found it – smack in the rodent's amygdala, an area associated with emotion and motivation.
So says a new study in the January 12 issue of the journal Cell.
Thanks to its use of optogenetics – a way to stimulate specific neurons with laser light – the Yale team was able to isolate one set of neurons that controls the pursuit of prey and another that signals the use of the jaw and neck muscles to bite down and deliver the kill to prey.
"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 study lead Ivan de Araujo in a statement.
By "object," the researcher meant pretty much anything – even bottle caps and wooden sticks were not safe from the pounce, if a mouse's hunting neurons were lit by the laser.
de Araujo pointed out that the aggression he and his team were able to stimulate in the rodent was not an all-purpose emotion. "The system is not just generalized aggression," he said. "It seems to be related to the animal's interest in obtaining food." The scientists observed that mice that were hungrier went harder after prey objects – sometimes live crickets, sometimes the bottles and sticks – than did mice that were less in the mood for food.
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de Araujo had been interested in gaining a better understanding of the neural mechanisms at work when animals engage in feeding behavior, and poring over other research he zeroed in on a brain area that dealt almost singularly with hunting but not eating: the central nucleus of the amygdala, which was also linked to control over hunting muscles like such as the neck and jaw.
Predatory behavior among jawed vertebrates like mice – and humans – de Araujo said, is "a major evolutionary player in shaping the brain." So, he thought: "There must be some primordial sub-cortical pathway that connects sensory input to the movement of the jaw and the biting."
The authors write that the mechanisms in the vertebrate brain that control hunting are not well known. Now, though, they say they have documented a critical player in the process. Their findings, they say, "suggest that central amygdala neurons instruct predatory hunting across jawed vertebrates."
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