The part of the brain that governs emotions such as fear and anxiety also helps mice hunt. That structure, the amygdala, orchestrates a mouse’s ability to both stalk a cricket and deliver a fatal bite, scientists report January 12 in Cell.
Scientists made select nerve cells in mice’s brains sensitive to light, and then used lasers to activate specific groups of those cells. By turning different cells on and off, the researchers found two separate sets of nerve cells relaying hunting-related messages from the amygdala’s central nucleus. One set controlled the mice’s ability to chase their prey. The other affected their ability to deliver a solid chomp and kill a cricket.
“They’ve found these two behaviors — that are part of something we think of being very complex — are controlled by these two circuits,” says Cris Niell, a neuroscientist at the University of Oregon in Eugene who wasn’t part of the study. “You flip a switch to chase, you flip a switch to attack.”
Ramping both of those circuits up to high power at the same time even led mice to chase and capture a tiny bug-shaped robot that they would normally ignore or avoid.
“The central amygdala has been conceptualized as a center for emotion and fear and threat detection,” says study coauthor Ivan de Araujo, a neuroscientist at the John B. Pierce Laboratory in New Haven, Conn. Now, it seems that the structure also controls the relatively complex task of hunting.
Scientists don’t know how the new function relates to the amygdala’s better-known role as an emotional control center. But the amygdala does help control heart rate and blood pressure, which shift in emotionally charged situations but also need to be regulated when an animal is pursuing prey, de Araujo says.
The study also shows how even a complex task like hunting can be coordinated by different groups of very specialized nerve cells, or neurons, working together. In this case, one set of neurons made a signaling pathway that controlled chasing, while another controlled biting. Together, those neurons helped the mice grab dinner.
“I think over the years we’ve become progressively more surprised by the behavioral specificity of these particular pathways,” says Anthony Leonardo, a neuroscientist at the Howard Hughes Medical Institute’s Janelia Research Campus in Ashburn, Va. “Certainly the evidence is mounting for a very strongly specific role for neurons.” Leonardo has found similarly specialized neurons in the dragonfly brain, with groups of neurons that run in parallel to each other controlling different types of movements.
Next, de Araujo says, his lab hopes to figure out what flips the neural switches in a mouse’s brain — how seeing or smelling potential prey triggers the amygdala to send the critter after a meal.
W. Han et al. Integrated control of predatory hunting by the central nucleus of the amygdala. Cell. Vol. 168, January 12, 2017, p. 1. doi: 10.1016/j.cell.2016.12.027.
S. Gaidos. Mapping aggression circuits in the brain. Science News. Vol. 187, March 21, 2015, p. 18.