Mice turn into predatory killers at the flash of a laser

To us humans, mice seem like pretty placid creatures – especially those domesticated to live in cages. But scientists from Yale University have discovered that they can switch on and off a rodent’s predatory hunting instincts by targeting specific neurons in the amygdala with light stimulation.

Using optogenetics (activating specific neurons in the brain via laser), the researchers could actively control the behaviour of the mice. With the lasers off, the rodents would go about their normal mousey business, but when switched on, the mice became uncontrollably aggressive, attacking and biting anything they could get their paws on – from bottle caps to live insects.

“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,” explained Ivan de Araujo, associate professor of psychiatry at Yale University.

What’s interesting is that despite the mice believing in their frenzied state that bottle caps and wooden sticks presented an existential threat, there was clearly a degree of control going on, as they never targeted other mice in these moments of aggression. What’s also rather telling is that how aggressively any mouse would pursue its prey was relative to when it last ate. “The system is not just generalised aggression. It seems to be related to the animal’s interest in obtaining food.” Well, we’ve all been known to lash out when we’re a bit peckish, I suppose.

Discovering that one set of neurons controls pursuit while another controls attack, the researchers found that they could fine-tune the way the rodent approached an attack. Lesioning the neurons responsible for biting and killing, for example, would leave the mouse chasing down its target but without the killer instinct necessary to finish the job – its jaw force was decreased by 50%. “They fail to deliver the killing bite,” de Araujo explained, which must be really confusing for the mouse.

The next step is to look into what triggers these neurons to fire and how the two modules are co-ordinated. “We now have a grip on their anatomical identities, so we hope we can manipulate them even more precisely in the future,” says de Araujo.

Image: British Pest Control Association, used under Creative Commons

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