Leslie Nemo in Scientific American:
Pinpointing where motivation resides in the brain is not easy, but a research team in China may have done just that. The group isolated a small group of neurons in the brains of mice that play a critical role in persistent behavior, according to a study published today in Science. This handful of brain cells is known as the dorsomedial prefrontal cortex, or dmPFC, and it sits in a region integral for learning appropriate social behavior. When the team fired up the neurons using light, the dmPFC motivated the mice to win competitions in which they had previously lacked the will to succeed. In other words, “this might provide a new biological basis for what people call ‘grit,’” says Hailan Hu, a neuroscientist at Zhejiang University who led the research.
In the case of these mice, “grit” requires upsetting hierarchies. Male mice that live together establish and maintain social rankings, Hu explains. To figure out which mice were dominant, she and her colleagues released two mice at a time into a narrow tube, one at each end. To get out, one animal—the lower-ranked individual—had to back up whereas the other, higher-ranking individual had to push forward. Most studies of mouse social hierarchy have focused on more aggressive behaviors such as how male mice might pick on new cage members, says Helmut Kessels, a neurologist at the Netherlands Institute for Neuroscience who was not involved with the research. “In this case it’s just four mice in a cage who live in peace,” he says, which helps strengthen the team’s argument that they were assessing motivation, not hostility.