mouse brain patterns hint at why

Joylessness triggered by stress creates a distinct brain signature, according to research in mice¹. The study also reveals one brain pattern that seems to confer resilience to stress ― and another that makes stressed animals less likely to feel pleasure, a core symptom of depression.

These findings, published today in Nature, offer clues as to how the brain gives rise to anhedonia, a resistance to enjoyment and pleasure. The results also provide a new avenue for treating the condition ― if the findings are validated in humans.

“Their approach in this study is spot on,” says Conor Liston, a neuroscientist at Weill Cornell Medicine in New York City, who was not involved in the work. The experiments fill “a big gap”, he says. “Anhedonia is something we don’t understand very well.”

A distressing symptom

More than 70% of people with severe depression experience anhedonia, which is also common in those with schizophrenia, Parkinson’s disease and other neurological and psychiatric conditions.

The symptom is notoriously difficult to treat, even in those taking medication, Liston says. “Anhedonia is something that patients care about the most, and feel like it’s least addressed by current treatments,” he says.

A journey into the causes and effects of depression

To understand how the brain gives rise to anhedonia, Mazen Kheirbek, a systems neuroscientist at the University of California, San Francisco, and his colleagues studied mice that had been placed under stress by exposure to larger, more aggressive mice.

Typically, mice have a sweet tooth and prefer sugar water over plain water if given the option. But some stressed mice instead preferred plain water ― which Kheirbek and his colleagues interpreted as a rodent version of anhedonia. Other mice subjected to the same stress preferred the sugar water. The authors labelled these animals ‘resilient’.