Chronic stress is associated with sleep disturbance. In their new study, Lu Huang and colleagues identify the neural pathway behind this behavior, and at the same time, explain how bright-light treatment is able to counter it. The research was conducted in mice. Bright-light treatment is known to improve sleep in those with sleep disorders, but how it works—and whether it works in cases of stress-induced sleep disturbances—was unknown. The researchers hypothesized that a part of the brain called the lateral habenula is deeply involved in this phenomenon because it both receives light signals from the eyes and can influence other...