Flash one light, and the mouse goes on the prowl, zombie-like, stalking any prey in its path. Flash another, and it delivers a killing blow with its teeth. The mouse doesn't hunt out of hunger — scientists are in control.
Image: Ivan De Araujo
Those scientists were studying how the vertebrate brain controls hunting behaviour, something that is not well-understood. They hypothesised that one part, the central nucleus of the amygdala, plays a key role. While omnivorous mice normally opt for plants over meat, the researchers found that they could turn their furry subjects into hunters, break their hunting behaviour into a pair of simpler ones after a slew of experiments and control those behaviours individually.
"Although we had some indications that the central nucleus of the amygdala could be important for hunting behaviour, it hasn't been observed before," lead investigator Ivan de Araujo, an associate professor of psychiatry at Yale, told Gizmodo. "It was surprising to see how clear the results were."
The scientists first injected the specific brain region with an infectious virus containing a light-sensitive gene. Soon the targeted neurons, or brain cells, began displaying that same light sensitivity. "We put a thin optic fibre into the head of the animal," said de Araujo, and "in turn connected [it] to a blue laser source." The neurons collected more positive charge in response to the blue light, and fired. "We could turn the neurons on and off based on our experimental design."
The group realised that one circuit of neurons controlled prey pursuit, while another controlled the face and head muscles to deliver the killing blow. More importantly, the researchers could target both or just one of the two behaviours, biting or pursuing, thus breaking the complex hunting behaviour into its basic parts. They published their results in the journal Cell today.
Image: Barry Green
Scientists not involved with the study were incredibly impressed with the robustness of the results — two people I spoke to used the phrase "tour-de-force". "What I think is impressive about the paper is that they applied these really cutting edge tools in exactly the right ways in the right places," said Bart Borghuis, assistant professor of anatomical sciences and neurobiology at the University of Louisville School of Medicine. "Both the science and method is impressive."
Others agreed. "I thought it was a really excellent piece of work," said Scott Sternson, a neuroscientist at the Janelia Research Campus of the Howard Hughes Medical Institute in Virginia. "It was able to very elegantly dissect a complex behaviour of prey capture in mice by precisely manipulating the different populations of neurons in a tiny part of the mouse brain."
Image: Ivan de Araujo
I asked de Araujo how he thought this research could be applied to us humans, since we also have a central nucleus in our amygdala. While it hasn't been demonstrated yet, he speculated that these regions might control hunting in humans as well. Most of us don't need our hunting behaviours any more since we don't hunt for our food. But de Araujo thought that maybe some of our opportunistic feeding behaviours, like overeating, could be controlled by the same brain region. An experiment would need to prove that.
De Araujo also cautioned that these brain centres don't control aggression, so he wasn't creating violent zombie mice. "It's very specific to animals attacking things that are food," he said. The mice didn't harm other mice, but they did attack small, fake insects. So don't expect to see world governments weaponising an army of mind-controlled zombie mice any time soon.