Using a technique called optogenetics – which involves activating neurons with light – scientists have managed to turn on mice’s predatory urges, causing them to viciously attack and try to “kill” inanimate objects like sticks and bottle caps.
However, the rodents did not assault other mice, suggesting that they had not been turned into mindless, indiscriminate killers, but were instead experiencing a voracious need to obtain food.
The international team focused on a part of the brain called the amygdala, which controls emotion and anger, among other things. In particular, they were interested in tinkering with a small region called the central amygdala, which contains several populations of neurons that communicate with various other areas of the brain.
One such population runs from the central amygdala to the reticular formation in the brainstem, which helps to coordinate the jaw muscles. Because of this, the team suspected that by playing around with these neurons they may be able to control the animals’ impulse to bite and kill.
Another population of neurons connects the central amygdala to the midbrain periaqueductal gray matter, which has been shown in previous studies to control predatory behaviors like stalking and pursuing prey.
The researchers therefore hoped to be able to manipulate the mice’s attempts to both catch and kill prey by playing around with these two sets of neurons.
Revealing their results in the journal Cell, the study authors explain how activating these neuronal projections with lasers caused the mice to hunt down and aggressively bite a range of objects. In a statement, study co-author Ivan de Araujo described how “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.”
When activating only the neurons that control the pursuit, but not those that control the kill, the team found that the mice would stalk and chase their prey, but would then only nibble at it rather than going in for the killer bite.
Given that jawed vertebrates are the planet’s top predators, these findings help to shed light on how these animals achieved their superior status, by revealing how the brain coordinates attacks on prey and allows for the delivery of lethal bites.