A recent Yale study sought to explain the neurological origin for hunting, an intrinsic behavior conserved across most vertebrate life.
In a paper published on Jan. 12 in Cell, the team that undertook the study pinpointed two subgroups of neurons within the central amygdala region of a mouse’s brain that, when activated, cause the mouse to stalk prey and exhibit a chewing-like jaw movement, respectively.
Before the study “it wasn’t clear how the brain was possessing and putting together a bunch of information in order to properly perform hunting behavior,” co-author Luis Tellez said. He added that hunting behavior is a relatively complex activity because it requires identification, tracking and killing of prey.
According to corresponding author Ivan de Araujo, the researchers chose to study hunting behavior in order to explore the natural origins of their lab’s main focus: feeding behavior.
“Predatory behavior is probably the most primordial, the most basic mechanism for acquiring food in vertebrate animals,” de Araujo said.
The team used both optogenetics, the use of light to control cells in living tissue, and chemogenetics, the processes by which macromolecules can be engineered to interact with previously unrecognized small molecules, to study the central amygdala region in mice. First, they engineered mice in which the two neuronal subgroups of interest could be activated using a laser. When the laser source was on, mice would attack, seize and ingest both crickets and nonedible objects, but this activity stopped as soon as the laser was turned off.
The use of optogenetics was crucial, Tellez said, as it is “the new standard for system neuroscience and also for circuitry distinction.”
The team then applied chemogenetics, another cutting-edge technique, to replicate their results without the disadvantages of optogenetics, which include brain implants and poor inhibitory control, de Araujo said.
According to the study, the researchers concluded that the central amygdala regulated hunting behavior in mice. Since all jawed vertebrates have a homologous brain region, it is logical that these results might be generalizable for other species, he added.
De Araujo noted that the study’s activation of the central amygdala has been misinterpreted as triggering a killer instinct in the mice.
Although mice whose central amygdala neurons were stimulated exhibited aggressive behavior, “this is a behavior that is triggered by the need for food and not as a killer mechanism,” he said.
Some of the other publicity surrounding the study has erroneously compared the mice’s behavior to that of zombies, first author Wenfei Han said. While zombies are portrayed as cannibalistic in popular culture, the mice did not behave aggressively towards each other, she added.
De Araujo said this finding — that the mice did not attack other mice even as they were observed to hunt and bite edible and nonedible objects indiscriminately — may have larger implications for understanding the roots of aggressive behaviors.
“That means that there is a recognition mechanism in the brain that detects the presence of a member of the same species and aborts predatory behavior,” he said. Psychologists have speculated that a defective aborting mechanism may be the cause of premeditated aggressive behaviors in humans, de Araujo added.
Han, a former dentist, said that the discovery of the central amygdala’s role in jaw movement may also help to explain teeth grinding, a common, yet poorly-understood human behavior.
There were restrictions in some of the methodologies used, and the researchers were not able to collect potentially useful data such as velocity of each mouse as it hunted, Tellez said. There is also debate as to whether the central amygdala is a cohesive region of the brain or simply a collection of adjacent neurons, de Araujo said, adding that as a result, the researchers may be guilty of providing an oversimplified interpretation of the functions of that region.
The team’s findings have raised a host of new neurological questions, Tellez said.
“Now we know that the central amygdala is very important for hunting behavior, but what we don’t know is how the amygdala processes and integrates this information and what kinds of parameters the animal needs to perform the behavior,” he said.
Additionally, previous research on the central amygdala has focused on fear and stress, so future studies will have to reveal the pathways that connect hunting behavior to these two emotions, Han said.
The only vertebrate without a sophisticated central amygdala region is the jawless lamprey.