Scientists discover trigger point for kill instinct in mice using lasers

Researchers at Yale say they may have pinpointed the neurons in which hunting behaviour originates in most vertebrates.

Scientists focussing on the function of the central amygdala (typically associated with fear or emotions) activated two neuron regions in the brains of mice with lasers and observed that they were able to trigger a predatory instinct in the animals.

They used a method called optogenetics, which made the neuron cells sensitive to blue light. The first time researcher Wenfei Han switched on blue lasers targeted at the mouse’s amygdala, she said she noticed the mouse suddenly voraciously bite into wood and some cotton that it was playing with.

“I was surprised!” Han told Global News. “We saw the mouse grab and bite very hard through wood, which he wouldn’t enormally eat in nature.”

Ivan de Araujo, senior author and Associate Professor of Psychiatry at Yale University, said they observed the different muscles controlled by the two neuron sets.

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“This area, the central amygdala, seems to allow the animal precise control over the muscles involved in pursuing and capturing prey,” he said.

Tweet This Click to share quote on Twitter: "This area, the central amygdala, seems to allow the animal precise control over the muscles involved in pursuing and capturing prey," he said.

One set of neurons seemed to activate the muscles associated with the pursuit of the prey, the second set activated the jaw muscles used to bite down and kill the prey.

The scientists used various prey with the mice, from inanimate objects such as wooden sticks to live prey like crickets.

Video footage published with their findings in the journal Cell shows the mice exhibiting normal, calm behaviour with the lasers off. Once the lasers are activated the mice chase and attack its prey.

However, Han said that this behaviour wasn’t exhibited when two mice (a male and female) were present.

“The male mouse very happily followed the female around. When we turned on the laser, he approached the female and licked her. He groomed the female,” said Han. “There must be an inhibitory input [to the central amygdala] to tell him to groom, not fight or bite.”

Tweet This Click to share quote on Twitter: "The male mouse very happily followed the female around. When we turned on the laser, he approached the female and licked her. He groomed the female," said Han. "There must be an inhibitory input [to the central amygdala] to tell him to groom, not fight or bite."

So could this predatory trigger be used on human brains, too?

In her literature review, Han said other researchers found that similar stimulation in a human would result in eating more food, not necessarily killing for the food.

“We think the central amygdala is like a gate for all the upstream information for feeling threatened, safe, hungry or not – all this information goes to the central amygdala and it acts like a gate for the movement, commanding to go or not go.”

Now the scientists are moving on to finding out what triggers predatory behaviour and how the two neuron sets coordinate to result in that behaviour.

“You feel amazed by how the brain’s designed. All the neuron pathways are much more complicated than we thought before!” said Han.

Tweet This Click to share quote on Twitter: "You feel amazed by how the brain's designed. All the neuron pathways are much more complicated than we thought before!" said Han.